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POSIX_MEMALIGN(3)	   Linux Programmers Manual	    POSIX_MEMALIGN(3)

       posix_memalign, memalign, valloc - Allocate aligned memory


       int posix_memalign(void **memptr, size_t alignment, size_t size);


       void *valloc(size_t size);
       void *memalign(size_t boundary, size_t size);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       posix_memalign(): _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600

       The  function  posix_memalign()	allocates  size  bytes	and places the
       address of the allocated memory in *memptr.  The address of  the  allo
       cated  memory will be a multiple of alignment, which must be a power of
       two and a multiple of sizeof(void *).

       The obsolete function memalign() allocates size	bytes  and  returns  a
       pointer to the allocated memory.  The memory address will be a multiple
       of boundary, which must be a power of two.

       The obsolete function valloc()  allocates  size	bytes  and  returns  a
       pointer to the allocated memory.  The memory address will be a multiple
       of the page  size.   It	is  equivalent	to  memalign(sysconf(_SC_PAGE

       For all three routines, the memory is not zeroed.

       memalign()  and valloc() return the pointer to the allocated memory, or
       NULL if the request fails.

       posix_memalign() returns zero on success, or one of  the  error	values
       listed in the next section on failure.  Note that errno is not set.

       EINVAL The alignment argument was not a power of two, or was not a mul
	      tiple of sizeof(void *).

       ENOMEM There was insufficient memory to fulfill the allocation request.

       The  functions memalign() and valloc() have been available in all Linux
       libc libraries.	The function posix_memalign() is available since glibc

       The  function  valloc()	appeared in 3.0BSD.  It is documented as being
       obsolete in 4.3BSD, and as legacy in SUSv2.   It  does  not  appear  in
       POSIX.1-2001.   The  function memalign() appears in SunOS 4.1.3 but not
       in 4.4BSD.  The function posix_memalign() comes from POSIX.1d.

       Everybody agrees that posix_memalign() is declared in .

       On some	systems  memalign()  is  declared  in    instead  of

       According  to  SUSv2,  valloc() is declared in .  Libc4,5 and
       glibc declare it in  and perhaps also in   (namely,
       if _GNU_SOURCE is defined, or _BSD_SOURCE is defined, or, for glibc, if
       _XOPEN_SOURCE_EXTENDED is defined, or, equivalently,  _XOPEN_SOURCE  is
       defined to a value not less than 500).

       On  many  systems  there  are  alignment  restrictions, for example, on
       buffers used for direct block device I/O.  POSIX  specifies  the  path
       conf(path,_PC_REC_XFER_ALIGN) call that tells what alignment is needed.
       Now one can use posix_memalign() to satisfy this requirement.

       posix_memalign()  verifies  that  alignment  matches  the  requirements
       detailed above.	memalign() may not check that the boundary argument is

       POSIX requires that memory obtained from posix_memalign() can be  freed
       using free(3).  Some systems provide no way to reclaim memory allocated
       with memalign() or valloc() (because one can only  pass	to  free(3)  a
       pointer	gotten	from  malloc(3),  while, for example, memalign() would
       call malloc(3) and then align the obtained value).  The glibc implemen
       tation  allows  memory  obtained from any of these three routines to be
       reclaimed with free(3).

       The glibc malloc(3) always returns 8-byte aligned memory addresses,  so
       these  routines are only needed if you require larger alignment values.

       brk(2), getpagesize(2), free(3), malloc(3)

       This page is part of release 3.05 of the Linux  man-pages  project.   A
       description  of	the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

GNU				  2007-07-26		     POSIX_MEMALIGN(3)

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