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954 lines
33 KiB
C
954 lines
33 KiB
C
/*
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A version of malloc/free/realloc written by Doug Lea and released to the
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public domain. Send questions/comments/complaints/performance data
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to dl@cs.oswego.edu
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* VERSION 2.6.6 Sun Mar 5 19:10:03 2000 Doug Lea (dl at gee)
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Note: There may be an updated version of this malloc obtainable at
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ftp://g.oswego.edu/pub/misc/malloc.c
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Check before installing!
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* Why use this malloc?
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This is not the fastest, most space-conserving, most portable, or
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most tunable malloc ever written. However it is among the fastest
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while also being among the most space-conserving, portable and tunable.
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Consistent balance across these factors results in a good general-purpose
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allocator. For a high-level description, see
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http://g.oswego.edu/dl/html/malloc.html
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* Synopsis of public routines
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(Much fuller descriptions are contained in the program documentation below.)
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malloc(size_t n);
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Return a pointer to a newly allocated chunk of at least n bytes, or null
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if no space is available.
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free(Void_t* p);
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Release the chunk of memory pointed to by p, or no effect if p is null.
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realloc(Void_t* p, size_t n);
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Return a pointer to a chunk of size n that contains the same data
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as does chunk p up to the minimum of (n, p's size) bytes, or null
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if no space is available. The returned pointer may or may not be
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the same as p. If p is null, equivalent to malloc. Unless the
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#define REALLOC_ZERO_BYTES_FREES below is set, realloc with a
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size argument of zero (re)allocates a minimum-sized chunk.
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memalign(size_t alignment, size_t n);
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Return a pointer to a newly allocated chunk of n bytes, aligned
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in accord with the alignment argument, which must be a power of
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two.
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valloc(size_t n);
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Equivalent to memalign(pagesize, n), where pagesize is the page
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size of the system (or as near to this as can be figured out from
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all the includes/defines below.)
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pvalloc(size_t n);
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Equivalent to valloc(minimum-page-that-holds(n)), that is,
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round up n to nearest pagesize.
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calloc(size_t unit, size_t quantity);
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Returns a pointer to quantity * unit bytes, with all locations
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set to zero.
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cfree(Void_t* p);
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Equivalent to free(p).
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malloc_trim(size_t pad);
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Release all but pad bytes of freed top-most memory back
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to the system. Return 1 if successful, else 0.
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malloc_usable_size(Void_t* p);
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Report the number usable allocated bytes associated with allocated
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chunk p. This may or may not report more bytes than were requested,
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due to alignment and minimum size constraints.
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malloc_stats();
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Prints brief summary statistics on stderr.
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mallinfo()
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Returns (by copy) a struct containing various summary statistics.
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mallopt(int parameter_number, int parameter_value)
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Changes one of the tunable parameters described below. Returns
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1 if successful in changing the parameter, else 0.
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* Vital statistics:
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Alignment: 8-byte
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8 byte alignment is currently hardwired into the design. This
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seems to suffice for all current machines and C compilers.
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Assumed pointer representation: 4 or 8 bytes
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Code for 8-byte pointers is untested by me but has worked
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reliably by Wolfram Gloger, who contributed most of the
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changes supporting this.
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Assumed size_t representation: 4 or 8 bytes
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Note that size_t is allowed to be 4 bytes even if pointers are 8.
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Minimum overhead per allocated chunk: 4 or 8 bytes
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Each malloced chunk has a hidden overhead of 4 bytes holding size
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and status information.
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Minimum allocated size: 4-byte ptrs: 16 bytes (including 4 overhead)
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8-byte ptrs: 24/32 bytes (including, 4/8 overhead)
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When a chunk is freed, 12 (for 4byte ptrs) or 20 (for 8 byte
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ptrs but 4 byte size) or 24 (for 8/8) additional bytes are
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needed; 4 (8) for a trailing size field
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and 8 (16) bytes for free list pointers. Thus, the minimum
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allocatable size is 16/24/32 bytes.
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Even a request for zero bytes (i.e., malloc(0)) returns a
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pointer to something of the minimum allocatable size.
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Maximum allocated size: 4-byte size_t: 2^31 - 8 bytes
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8-byte size_t: 2^63 - 16 bytes
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It is assumed that (possibly signed) size_t bit values suffice to
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represent chunk sizes. `Possibly signed' is due to the fact
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that `size_t' may be defined on a system as either a signed or
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an unsigned type. To be conservative, values that would appear
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as negative numbers are avoided.
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Requests for sizes with a negative sign bit when the request
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size is treaded as a long will return null.
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Maximum overhead wastage per allocated chunk: normally 15 bytes
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Alignnment demands, plus the minimum allocatable size restriction
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make the normal worst-case wastage 15 bytes (i.e., up to 15
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more bytes will be allocated than were requested in malloc), with
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two exceptions:
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1. Because requests for zero bytes allocate non-zero space,
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the worst case wastage for a request of zero bytes is 24 bytes.
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2. For requests >= mmap_threshold that are serviced via
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mmap(), the worst case wastage is 8 bytes plus the remainder
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from a system page (the minimal mmap unit); typically 4096 bytes.
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* Limitations
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Here are some features that are NOT currently supported
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* No user-definable hooks for callbacks and the like.
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* No automated mechanism for fully checking that all accesses
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to malloced memory stay within their bounds.
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* No support for compaction.
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* Synopsis of compile-time options:
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People have reported using previous versions of this malloc on all
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versions of Unix, sometimes by tweaking some of the defines
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below. It has been tested most extensively on Solaris and
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Linux. It is also reported to work on WIN32 platforms.
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People have also reported adapting this malloc for use in
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stand-alone embedded systems.
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The implementation is in straight, hand-tuned ANSI C. Among other
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consequences, it uses a lot of macros. Because of this, to be at
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all usable, this code should be compiled using an optimizing compiler
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(for example gcc -O2) that can simplify expressions and control
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paths.
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__STD_C (default: derived from C compiler defines)
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Nonzero if using ANSI-standard C compiler, a C++ compiler, or
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a C compiler sufficiently close to ANSI to get away with it.
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DEBUG (default: NOT defined)
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Define to enable debugging. Adds fairly extensive assertion-based
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checking to help track down memory errors, but noticeably slows down
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execution.
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REALLOC_ZERO_BYTES_FREES (default: NOT defined)
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Define this if you think that realloc(p, 0) should be equivalent
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to free(p). Otherwise, since malloc returns a unique pointer for
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malloc(0), so does realloc(p, 0).
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HAVE_MEMCPY (default: defined)
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Define if you are not otherwise using ANSI STD C, but still
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have memcpy and memset in your C library and want to use them.
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Otherwise, simple internal versions are supplied.
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USE_MEMCPY (default: 1 if HAVE_MEMCPY is defined, 0 otherwise)
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Define as 1 if you want the C library versions of memset and
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memcpy called in realloc and calloc (otherwise macro versions are used).
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At least on some platforms, the simple macro versions usually
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outperform libc versions.
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HAVE_MMAP (default: defined as 1)
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Define to non-zero to optionally make malloc() use mmap() to
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allocate very large blocks.
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HAVE_MREMAP (default: defined as 0 unless Linux libc set)
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Define to non-zero to optionally make realloc() use mremap() to
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reallocate very large blocks.
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malloc_getpagesize (default: derived from system #includes)
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Either a constant or routine call returning the system page size.
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HAVE_USR_INCLUDE_MALLOC_H (default: NOT defined)
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Optionally define if you are on a system with a /usr/include/malloc.h
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that declares struct mallinfo. It is not at all necessary to
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define this even if you do, but will ensure consistency.
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INTERNAL_SIZE_T (default: size_t)
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Define to a 32-bit type (probably `unsigned int') if you are on a
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64-bit machine, yet do not want or need to allow malloc requests of
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greater than 2^31 to be handled. This saves space, especially for
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very small chunks.
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INTERNAL_LINUX_C_LIB (default: NOT defined)
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Defined only when compiled as part of Linux libc.
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Also note that there is some odd internal name-mangling via defines
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(for example, internally, `malloc' is named `mALLOc') needed
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when compiling in this case. These look funny but don't otherwise
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affect anything.
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WIN32 (default: undefined)
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Define this on MS win (95, nt) platforms to compile in sbrk emulation.
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LACKS_UNISTD_H (default: undefined if not WIN32)
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Define this if your system does not have a <unistd.h>.
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LACKS_SYS_PARAM_H (default: undefined if not WIN32)
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Define this if your system does not have a <sys/param.h>.
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MORECORE (default: sbrk)
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The name of the routine to call to obtain more memory from the system.
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MORECORE_FAILURE (default: -1)
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The value returned upon failure of MORECORE.
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MORECORE_CLEARS (default 1)
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True (1) if the routine mapped to MORECORE zeroes out memory (which
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holds for sbrk).
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DEFAULT_TRIM_THRESHOLD
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DEFAULT_TOP_PAD
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DEFAULT_MMAP_THRESHOLD
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DEFAULT_MMAP_MAX
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Default values of tunable parameters (described in detail below)
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controlling interaction with host system routines (sbrk, mmap, etc).
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These values may also be changed dynamically via mallopt(). The
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preset defaults are those that give best performance for typical
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programs/systems.
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USE_DL_PREFIX (default: undefined)
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Prefix all public routines with the string 'dl'. Useful to
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quickly avoid procedure declaration conflicts and linker symbol
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conflicts with existing memory allocation routines.
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*/
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#ifndef __MALLOC_H__
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#define __MALLOC_H__
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/* Preliminaries */
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#ifndef __STD_C
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#ifdef __STDC__
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#define __STD_C 1
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#else
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#if __cplusplus
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#define __STD_C 1
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#else
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#define __STD_C 0
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#endif /*__cplusplus*/
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#endif /*__STDC__*/
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#endif /*__STD_C*/
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#ifndef Void_t
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#if (__STD_C || defined(WIN32))
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#define Void_t void
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#else
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#define Void_t char
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#endif
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#endif /*Void_t*/
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#if __STD_C
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#include <linux/stddef.h> /* for size_t */
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#else
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#include <sys/types.h>
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#endif /* __STD_C */
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#ifdef __cplusplus
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extern "C" {
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#endif
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#if 0 /* not for U-Boot */
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#include <stdio.h> /* needed for malloc_stats */
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#endif
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/*
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Compile-time options
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*/
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/*
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Debugging:
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Because freed chunks may be overwritten with link fields, this
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malloc will often die when freed memory is overwritten by user
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programs. This can be very effective (albeit in an annoying way)
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in helping track down dangling pointers.
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If you compile with -DDEBUG, a number of assertion checks are
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enabled that will catch more memory errors. You probably won't be
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able to make much sense of the actual assertion errors, but they
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should help you locate incorrectly overwritten memory. The
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checking is fairly extensive, and will slow down execution
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noticeably. Calling malloc_stats or mallinfo with DEBUG set will
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attempt to check every non-mmapped allocated and free chunk in the
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course of computing the summmaries. (By nature, mmapped regions
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cannot be checked very much automatically.)
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Setting DEBUG may also be helpful if you are trying to modify
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this code. The assertions in the check routines spell out in more
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detail the assumptions and invariants underlying the algorithms.
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*/
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#ifdef DEBUG
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/* #include <assert.h> */
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#define assert(x) ((void)0)
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#else
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#define assert(x) ((void)0)
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#endif
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/*
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INTERNAL_SIZE_T is the word-size used for internal bookkeeping
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of chunk sizes. On a 64-bit machine, you can reduce malloc
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overhead by defining INTERNAL_SIZE_T to be a 32 bit `unsigned int'
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at the expense of not being able to handle requests greater than
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2^31. This limitation is hardly ever a concern; you are encouraged
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to set this. However, the default version is the same as size_t.
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*/
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#ifndef INTERNAL_SIZE_T
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#define INTERNAL_SIZE_T size_t
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#endif
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/*
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REALLOC_ZERO_BYTES_FREES should be set if a call to
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realloc with zero bytes should be the same as a call to free.
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Some people think it should. Otherwise, since this malloc
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returns a unique pointer for malloc(0), so does realloc(p, 0).
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*/
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/* #define REALLOC_ZERO_BYTES_FREES */
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/*
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WIN32 causes an emulation of sbrk to be compiled in
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mmap-based options are not currently supported in WIN32.
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*/
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/* #define WIN32 */
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#ifdef WIN32
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#define MORECORE wsbrk
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#define HAVE_MMAP 0
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#define LACKS_UNISTD_H
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#define LACKS_SYS_PARAM_H
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/*
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Include 'windows.h' to get the necessary declarations for the
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Microsoft Visual C++ data structures and routines used in the 'sbrk'
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emulation.
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Define WIN32_LEAN_AND_MEAN so that only the essential Microsoft
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Visual C++ header files are included.
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*/
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#define WIN32_LEAN_AND_MEAN
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#include <windows.h>
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#endif
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/*
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HAVE_MEMCPY should be defined if you are not otherwise using
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ANSI STD C, but still have memcpy and memset in your C library
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and want to use them in calloc and realloc. Otherwise simple
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macro versions are defined here.
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USE_MEMCPY should be defined as 1 if you actually want to
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have memset and memcpy called. People report that the macro
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versions are often enough faster than libc versions on many
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systems that it is better to use them.
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*/
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#define HAVE_MEMCPY
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#ifndef USE_MEMCPY
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#ifdef HAVE_MEMCPY
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#define USE_MEMCPY 1
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#else
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#define USE_MEMCPY 0
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#endif
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#endif
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#if (__STD_C || defined(HAVE_MEMCPY))
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#if __STD_C
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void* memset(void*, int, size_t);
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void* memcpy(void*, const void*, size_t);
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#else
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#ifdef WIN32
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/* On Win32 platforms, 'memset()' and 'memcpy()' are already declared in */
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/* 'windows.h' */
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#else
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Void_t* memset();
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Void_t* memcpy();
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#endif
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#endif
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#endif
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#if USE_MEMCPY
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/* The following macros are only invoked with (2n+1)-multiples of
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INTERNAL_SIZE_T units, with a positive integer n. This is exploited
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for fast inline execution when n is small. */
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#define MALLOC_ZERO(charp, nbytes) \
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do { \
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INTERNAL_SIZE_T mzsz = (nbytes); \
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if(mzsz <= 9*sizeof(mzsz)) { \
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INTERNAL_SIZE_T* mz = (INTERNAL_SIZE_T*) (charp); \
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if(mzsz >= 5*sizeof(mzsz)) { *mz++ = 0; \
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*mz++ = 0; \
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if(mzsz >= 7*sizeof(mzsz)) { *mz++ = 0; \
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*mz++ = 0; \
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if(mzsz >= 9*sizeof(mzsz)) { *mz++ = 0; \
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*mz++ = 0; }}} \
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*mz++ = 0; \
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*mz++ = 0; \
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*mz = 0; \
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} else memset((charp), 0, mzsz); \
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} while(0)
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#define MALLOC_COPY(dest,src,nbytes) \
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do { \
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INTERNAL_SIZE_T mcsz = (nbytes); \
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if(mcsz <= 9*sizeof(mcsz)) { \
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INTERNAL_SIZE_T* mcsrc = (INTERNAL_SIZE_T*) (src); \
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INTERNAL_SIZE_T* mcdst = (INTERNAL_SIZE_T*) (dest); \
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if(mcsz >= 5*sizeof(mcsz)) { *mcdst++ = *mcsrc++; \
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*mcdst++ = *mcsrc++; \
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if(mcsz >= 7*sizeof(mcsz)) { *mcdst++ = *mcsrc++; \
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*mcdst++ = *mcsrc++; \
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if(mcsz >= 9*sizeof(mcsz)) { *mcdst++ = *mcsrc++; \
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*mcdst++ = *mcsrc++; }}} \
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*mcdst++ = *mcsrc++; \
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*mcdst++ = *mcsrc++; \
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*mcdst = *mcsrc ; \
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} else memcpy(dest, src, mcsz); \
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} while(0)
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#else /* !USE_MEMCPY */
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/* Use Duff's device for good zeroing/copying performance. */
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#define MALLOC_ZERO(charp, nbytes) \
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do { \
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INTERNAL_SIZE_T* mzp = (INTERNAL_SIZE_T*)(charp); \
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long mctmp = (nbytes)/sizeof(INTERNAL_SIZE_T), mcn; \
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if (mctmp < 8) mcn = 0; else { mcn = (mctmp-1)/8; mctmp %= 8; } \
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switch (mctmp) { \
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case 0: for(;;) { *mzp++ = 0; \
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case 7: *mzp++ = 0; \
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case 6: *mzp++ = 0; \
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case 5: *mzp++ = 0; \
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case 4: *mzp++ = 0; \
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case 3: *mzp++ = 0; \
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case 2: *mzp++ = 0; \
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case 1: *mzp++ = 0; if(mcn <= 0) break; mcn--; } \
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} \
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} while(0)
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#define MALLOC_COPY(dest,src,nbytes) \
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do { \
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INTERNAL_SIZE_T* mcsrc = (INTERNAL_SIZE_T*) src; \
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INTERNAL_SIZE_T* mcdst = (INTERNAL_SIZE_T*) dest; \
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long mctmp = (nbytes)/sizeof(INTERNAL_SIZE_T), mcn; \
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if (mctmp < 8) mcn = 0; else { mcn = (mctmp-1)/8; mctmp %= 8; } \
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switch (mctmp) { \
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case 0: for(;;) { *mcdst++ = *mcsrc++; \
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case 7: *mcdst++ = *mcsrc++; \
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case 6: *mcdst++ = *mcsrc++; \
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case 5: *mcdst++ = *mcsrc++; \
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case 4: *mcdst++ = *mcsrc++; \
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case 3: *mcdst++ = *mcsrc++; \
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case 2: *mcdst++ = *mcsrc++; \
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case 1: *mcdst++ = *mcsrc++; if(mcn <= 0) break; mcn--; } \
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} \
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} while(0)
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#endif
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/*
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Define HAVE_MMAP to optionally make malloc() use mmap() to
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allocate very large blocks. These will be returned to the
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operating system immediately after a free().
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*/
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/***
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#ifndef HAVE_MMAP
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#define HAVE_MMAP 1
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#endif
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***/
|
||
#undef HAVE_MMAP /* Not available for U-Boot */
|
||
|
||
/*
|
||
Define HAVE_MREMAP to make realloc() use mremap() to re-allocate
|
||
large blocks. This is currently only possible on Linux with
|
||
kernel versions newer than 1.3.77.
|
||
*/
|
||
|
||
/***
|
||
#ifndef HAVE_MREMAP
|
||
#ifdef INTERNAL_LINUX_C_LIB
|
||
#define HAVE_MREMAP 1
|
||
#else
|
||
#define HAVE_MREMAP 0
|
||
#endif
|
||
#endif
|
||
***/
|
||
#undef HAVE_MREMAP /* Not available for U-Boot */
|
||
|
||
#if HAVE_MMAP
|
||
|
||
#include <unistd.h>
|
||
#include <fcntl.h>
|
||
#include <sys/mman.h>
|
||
|
||
#if !defined(MAP_ANONYMOUS) && defined(MAP_ANON)
|
||
#define MAP_ANONYMOUS MAP_ANON
|
||
#endif
|
||
|
||
#endif /* HAVE_MMAP */
|
||
|
||
/*
|
||
Access to system page size. To the extent possible, this malloc
|
||
manages memory from the system in page-size units.
|
||
|
||
The following mechanics for getpagesize were adapted from
|
||
bsd/gnu getpagesize.h
|
||
*/
|
||
|
||
#define LACKS_UNISTD_H /* Shortcut for U-Boot */
|
||
#define malloc_getpagesize 4096
|
||
|
||
#ifndef LACKS_UNISTD_H
|
||
# include <unistd.h>
|
||
#endif
|
||
|
||
#ifndef malloc_getpagesize
|
||
# ifdef _SC_PAGESIZE /* some SVR4 systems omit an underscore */
|
||
# ifndef _SC_PAGE_SIZE
|
||
# define _SC_PAGE_SIZE _SC_PAGESIZE
|
||
# endif
|
||
# endif
|
||
# ifdef _SC_PAGE_SIZE
|
||
# define malloc_getpagesize sysconf(_SC_PAGE_SIZE)
|
||
# else
|
||
# if defined(BSD) || defined(DGUX) || defined(HAVE_GETPAGESIZE)
|
||
extern size_t getpagesize();
|
||
# define malloc_getpagesize getpagesize()
|
||
# else
|
||
# ifdef WIN32
|
||
# define malloc_getpagesize (4096) /* TBD: Use 'GetSystemInfo' instead */
|
||
# else
|
||
# ifndef LACKS_SYS_PARAM_H
|
||
# include <sys/param.h>
|
||
# endif
|
||
# ifdef EXEC_PAGESIZE
|
||
# define malloc_getpagesize EXEC_PAGESIZE
|
||
# else
|
||
# ifdef NBPG
|
||
# ifndef CLSIZE
|
||
# define malloc_getpagesize NBPG
|
||
# else
|
||
# define malloc_getpagesize (NBPG * CLSIZE)
|
||
# endif
|
||
# else
|
||
# ifdef NBPC
|
||
# define malloc_getpagesize NBPC
|
||
# else
|
||
# ifdef PAGESIZE
|
||
# define malloc_getpagesize PAGESIZE
|
||
# else
|
||
# define malloc_getpagesize (4096) /* just guess */
|
||
# endif
|
||
# endif
|
||
# endif
|
||
# endif
|
||
# endif
|
||
# endif
|
||
# endif
|
||
#endif
|
||
|
||
|
||
/*
|
||
|
||
This version of malloc supports the standard SVID/XPG mallinfo
|
||
routine that returns a struct containing the same kind of
|
||
information you can get from malloc_stats. It should work on
|
||
any SVID/XPG compliant system that has a /usr/include/malloc.h
|
||
defining struct mallinfo. (If you'd like to install such a thing
|
||
yourself, cut out the preliminary declarations as described above
|
||
and below and save them in a malloc.h file. But there's no
|
||
compelling reason to bother to do this.)
|
||
|
||
The main declaration needed is the mallinfo struct that is returned
|
||
(by-copy) by mallinfo(). The SVID/XPG malloinfo struct contains a
|
||
bunch of fields, most of which are not even meaningful in this
|
||
version of malloc. Some of these fields are are instead filled by
|
||
mallinfo() with other numbers that might possibly be of interest.
|
||
|
||
HAVE_USR_INCLUDE_MALLOC_H should be set if you have a
|
||
/usr/include/malloc.h file that includes a declaration of struct
|
||
mallinfo. If so, it is included; else an SVID2/XPG2 compliant
|
||
version is declared below. These must be precisely the same for
|
||
mallinfo() to work.
|
||
|
||
*/
|
||
|
||
/* #define HAVE_USR_INCLUDE_MALLOC_H */
|
||
|
||
#if HAVE_USR_INCLUDE_MALLOC_H
|
||
#include "/usr/include/malloc.h"
|
||
#else
|
||
|
||
/* SVID2/XPG mallinfo structure */
|
||
|
||
struct mallinfo {
|
||
int arena; /* total space allocated from system */
|
||
int ordblks; /* number of non-inuse chunks */
|
||
int smblks; /* unused -- always zero */
|
||
int hblks; /* number of mmapped regions */
|
||
int hblkhd; /* total space in mmapped regions */
|
||
int usmblks; /* unused -- always zero */
|
||
int fsmblks; /* unused -- always zero */
|
||
int uordblks; /* total allocated space */
|
||
int fordblks; /* total non-inuse space */
|
||
int keepcost; /* top-most, releasable (via malloc_trim) space */
|
||
};
|
||
|
||
/* SVID2/XPG mallopt options */
|
||
|
||
#define M_MXFAST 1 /* UNUSED in this malloc */
|
||
#define M_NLBLKS 2 /* UNUSED in this malloc */
|
||
#define M_GRAIN 3 /* UNUSED in this malloc */
|
||
#define M_KEEP 4 /* UNUSED in this malloc */
|
||
|
||
#endif
|
||
|
||
/* mallopt options that actually do something */
|
||
|
||
#define M_TRIM_THRESHOLD -1
|
||
#define M_TOP_PAD -2
|
||
#define M_MMAP_THRESHOLD -3
|
||
#define M_MMAP_MAX -4
|
||
|
||
|
||
#ifndef DEFAULT_TRIM_THRESHOLD
|
||
#define DEFAULT_TRIM_THRESHOLD (128 * 1024)
|
||
#endif
|
||
|
||
/*
|
||
M_TRIM_THRESHOLD is the maximum amount of unused top-most memory
|
||
to keep before releasing via malloc_trim in free().
|
||
|
||
Automatic trimming is mainly useful in long-lived programs.
|
||
Because trimming via sbrk can be slow on some systems, and can
|
||
sometimes be wasteful (in cases where programs immediately
|
||
afterward allocate more large chunks) the value should be high
|
||
enough so that your overall system performance would improve by
|
||
releasing.
|
||
|
||
The trim threshold and the mmap control parameters (see below)
|
||
can be traded off with one another. Trimming and mmapping are
|
||
two different ways of releasing unused memory back to the
|
||
system. Between these two, it is often possible to keep
|
||
system-level demands of a long-lived program down to a bare
|
||
minimum. For example, in one test suite of sessions measuring
|
||
the XF86 X server on Linux, using a trim threshold of 128K and a
|
||
mmap threshold of 192K led to near-minimal long term resource
|
||
consumption.
|
||
|
||
If you are using this malloc in a long-lived program, it should
|
||
pay to experiment with these values. As a rough guide, you
|
||
might set to a value close to the average size of a process
|
||
(program) running on your system. Releasing this much memory
|
||
would allow such a process to run in memory. Generally, it's
|
||
worth it to tune for trimming rather tham memory mapping when a
|
||
program undergoes phases where several large chunks are
|
||
allocated and released in ways that can reuse each other's
|
||
storage, perhaps mixed with phases where there are no such
|
||
chunks at all. And in well-behaved long-lived programs,
|
||
controlling release of large blocks via trimming versus mapping
|
||
is usually faster.
|
||
|
||
However, in most programs, these parameters serve mainly as
|
||
protection against the system-level effects of carrying around
|
||
massive amounts of unneeded memory. Since frequent calls to
|
||
sbrk, mmap, and munmap otherwise degrade performance, the default
|
||
parameters are set to relatively high values that serve only as
|
||
safeguards.
|
||
|
||
The default trim value is high enough to cause trimming only in
|
||
fairly extreme (by current memory consumption standards) cases.
|
||
It must be greater than page size to have any useful effect. To
|
||
disable trimming completely, you can set to (unsigned long)(-1);
|
||
|
||
|
||
*/
|
||
|
||
|
||
#ifndef DEFAULT_TOP_PAD
|
||
#define DEFAULT_TOP_PAD (0)
|
||
#endif
|
||
|
||
/*
|
||
M_TOP_PAD is the amount of extra `padding' space to allocate or
|
||
retain whenever sbrk is called. It is used in two ways internally:
|
||
|
||
* When sbrk is called to extend the top of the arena to satisfy
|
||
a new malloc request, this much padding is added to the sbrk
|
||
request.
|
||
|
||
* When malloc_trim is called automatically from free(),
|
||
it is used as the `pad' argument.
|
||
|
||
In both cases, the actual amount of padding is rounded
|
||
so that the end of the arena is always a system page boundary.
|
||
|
||
The main reason for using padding is to avoid calling sbrk so
|
||
often. Having even a small pad greatly reduces the likelihood
|
||
that nearly every malloc request during program start-up (or
|
||
after trimming) will invoke sbrk, which needlessly wastes
|
||
time.
|
||
|
||
Automatic rounding-up to page-size units is normally sufficient
|
||
to avoid measurable overhead, so the default is 0. However, in
|
||
systems where sbrk is relatively slow, it can pay to increase
|
||
this value, at the expense of carrying around more memory than
|
||
the program needs.
|
||
|
||
*/
|
||
|
||
|
||
#ifndef DEFAULT_MMAP_THRESHOLD
|
||
#define DEFAULT_MMAP_THRESHOLD (128 * 1024)
|
||
#endif
|
||
|
||
/*
|
||
|
||
M_MMAP_THRESHOLD is the request size threshold for using mmap()
|
||
to service a request. Requests of at least this size that cannot
|
||
be allocated using already-existing space will be serviced via mmap.
|
||
(If enough normal freed space already exists it is used instead.)
|
||
|
||
Using mmap segregates relatively large chunks of memory so that
|
||
they can be individually obtained and released from the host
|
||
system. A request serviced through mmap is never reused by any
|
||
other request (at least not directly; the system may just so
|
||
happen to remap successive requests to the same locations).
|
||
|
||
Segregating space in this way has the benefit that mmapped space
|
||
can ALWAYS be individually released back to the system, which
|
||
helps keep the system level memory demands of a long-lived
|
||
program low. Mapped memory can never become `locked' between
|
||
other chunks, as can happen with normally allocated chunks, which
|
||
menas that even trimming via malloc_trim would not release them.
|
||
|
||
However, it has the disadvantages that:
|
||
|
||
1. The space cannot be reclaimed, consolidated, and then
|
||
used to service later requests, as happens with normal chunks.
|
||
2. It can lead to more wastage because of mmap page alignment
|
||
requirements
|
||
3. It causes malloc performance to be more dependent on host
|
||
system memory management support routines which may vary in
|
||
implementation quality and may impose arbitrary
|
||
limitations. Generally, servicing a request via normal
|
||
malloc steps is faster than going through a system's mmap.
|
||
|
||
All together, these considerations should lead you to use mmap
|
||
only for relatively large requests.
|
||
|
||
|
||
*/
|
||
|
||
|
||
#ifndef DEFAULT_MMAP_MAX
|
||
#if HAVE_MMAP
|
||
#define DEFAULT_MMAP_MAX (64)
|
||
#else
|
||
#define DEFAULT_MMAP_MAX (0)
|
||
#endif
|
||
#endif
|
||
|
||
/*
|
||
M_MMAP_MAX is the maximum number of requests to simultaneously
|
||
service using mmap. This parameter exists because:
|
||
|
||
1. Some systems have a limited number of internal tables for
|
||
use by mmap.
|
||
2. In most systems, overreliance on mmap can degrade overall
|
||
performance.
|
||
3. If a program allocates many large regions, it is probably
|
||
better off using normal sbrk-based allocation routines that
|
||
can reclaim and reallocate normal heap memory. Using a
|
||
small value allows transition into this mode after the
|
||
first few allocations.
|
||
|
||
Setting to 0 disables all use of mmap. If HAVE_MMAP is not set,
|
||
the default value is 0, and attempts to set it to non-zero values
|
||
in mallopt will fail.
|
||
*/
|
||
|
||
|
||
/*
|
||
USE_DL_PREFIX will prefix all public routines with the string 'dl'.
|
||
Useful to quickly avoid procedure declaration conflicts and linker
|
||
symbol conflicts with existing memory allocation routines.
|
||
|
||
*/
|
||
|
||
/* #define USE_DL_PREFIX */
|
||
|
||
|
||
/*
|
||
|
||
Special defines for linux libc
|
||
|
||
Except when compiled using these special defines for Linux libc
|
||
using weak aliases, this malloc is NOT designed to work in
|
||
multithreaded applications. No semaphores or other concurrency
|
||
control are provided to ensure that multiple malloc or free calls
|
||
don't run at the same time, which could be disasterous. A single
|
||
semaphore could be used across malloc, realloc, and free (which is
|
||
essentially the effect of the linux weak alias approach). It would
|
||
be hard to obtain finer granularity.
|
||
|
||
*/
|
||
|
||
|
||
#ifdef INTERNAL_LINUX_C_LIB
|
||
|
||
#if __STD_C
|
||
|
||
Void_t * __default_morecore_init (ptrdiff_t);
|
||
Void_t *(*__morecore)(ptrdiff_t) = __default_morecore_init;
|
||
|
||
#else
|
||
|
||
Void_t * __default_morecore_init ();
|
||
Void_t *(*__morecore)() = __default_morecore_init;
|
||
|
||
#endif
|
||
|
||
#define MORECORE (*__morecore)
|
||
#define MORECORE_FAILURE 0
|
||
#define MORECORE_CLEARS 1
|
||
|
||
#else /* INTERNAL_LINUX_C_LIB */
|
||
|
||
#if __STD_C
|
||
extern Void_t* sbrk(ptrdiff_t);
|
||
#else
|
||
extern Void_t* sbrk();
|
||
#endif
|
||
|
||
#ifndef MORECORE
|
||
#define MORECORE sbrk
|
||
#endif
|
||
|
||
#ifndef MORECORE_FAILURE
|
||
#define MORECORE_FAILURE -1
|
||
#endif
|
||
|
||
#ifndef MORECORE_CLEARS
|
||
#define MORECORE_CLEARS 1
|
||
#endif
|
||
|
||
#endif /* INTERNAL_LINUX_C_LIB */
|
||
|
||
#if defined(INTERNAL_LINUX_C_LIB) && defined(__ELF__)
|
||
|
||
#define cALLOc __libc_calloc
|
||
#define fREe __libc_free
|
||
#define mALLOc __libc_malloc
|
||
#define mEMALIGn __libc_memalign
|
||
#define rEALLOc __libc_realloc
|
||
#define vALLOc __libc_valloc
|
||
#define pvALLOc __libc_pvalloc
|
||
#define mALLINFo __libc_mallinfo
|
||
#define mALLOPt __libc_mallopt
|
||
|
||
#pragma weak calloc = __libc_calloc
|
||
#pragma weak free = __libc_free
|
||
#pragma weak cfree = __libc_free
|
||
#pragma weak malloc = __libc_malloc
|
||
#pragma weak memalign = __libc_memalign
|
||
#pragma weak realloc = __libc_realloc
|
||
#pragma weak valloc = __libc_valloc
|
||
#pragma weak pvalloc = __libc_pvalloc
|
||
#pragma weak mallinfo = __libc_mallinfo
|
||
#pragma weak mallopt = __libc_mallopt
|
||
|
||
#else
|
||
|
||
#ifdef USE_DL_PREFIX
|
||
#define cALLOc dlcalloc
|
||
#define fREe dlfree
|
||
#define mALLOc dlmalloc
|
||
#define mEMALIGn dlmemalign
|
||
#define rEALLOc dlrealloc
|
||
#define vALLOc dlvalloc
|
||
#define pvALLOc dlpvalloc
|
||
#define mALLINFo dlmallinfo
|
||
#define mALLOPt dlmallopt
|
||
#else /* USE_DL_PREFIX */
|
||
#define cALLOc calloc
|
||
#define fREe free
|
||
#define mALLOc malloc
|
||
#define mEMALIGn memalign
|
||
#define rEALLOc realloc
|
||
#define vALLOc valloc
|
||
#define pvALLOc pvalloc
|
||
#define mALLINFo mallinfo
|
||
#define mALLOPt mallopt
|
||
#endif /* USE_DL_PREFIX */
|
||
|
||
#endif
|
||
|
||
/* Public routines */
|
||
|
||
#if __STD_C
|
||
|
||
Void_t* mALLOc(size_t);
|
||
void fREe(Void_t*);
|
||
Void_t* rEALLOc(Void_t*, size_t);
|
||
Void_t* mEMALIGn(size_t, size_t);
|
||
Void_t* vALLOc(size_t);
|
||
Void_t* pvALLOc(size_t);
|
||
Void_t* cALLOc(size_t, size_t);
|
||
void cfree(Void_t*);
|
||
int malloc_trim(size_t);
|
||
size_t malloc_usable_size(Void_t*);
|
||
void malloc_stats(void);
|
||
int mALLOPt(int, int);
|
||
struct mallinfo mALLINFo(void);
|
||
#else
|
||
Void_t* mALLOc();
|
||
void fREe();
|
||
Void_t* rEALLOc();
|
||
Void_t* mEMALIGn();
|
||
Void_t* vALLOc();
|
||
Void_t* pvALLOc();
|
||
Void_t* cALLOc();
|
||
void cfree();
|
||
int malloc_trim();
|
||
size_t malloc_usable_size();
|
||
void malloc_stats();
|
||
int mALLOPt();
|
||
struct mallinfo mALLINFo();
|
||
#endif
|
||
|
||
/*
|
||
* Begin and End of memory area for malloc(), and current "brk"
|
||
*/
|
||
extern ulong mem_malloc_start;
|
||
extern ulong mem_malloc_end;
|
||
extern ulong mem_malloc_brk;
|
||
|
||
void mem_malloc_init(ulong start, ulong size);
|
||
|
||
#ifdef __cplusplus
|
||
}; /* end of extern "C" */
|
||
#endif
|
||
|
||
#endif /* __MALLOC_H__ */
|