compiler/stdc/malloc_align.c

   1 /*
   2     Copyright © 1995-2012, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     AROS extension function malloc_align().
   6 */
   7
   8 #include <exec/types.h>
   9
  10 #include "__memalign.h"
  11
  12 #include <errno.h>
  13
  14 #define powerof2(x) ((((x)-1)&(x))==0)
  15
  16 /*****************************************************************************
  17
  18     NAME */
  19 #include <stdlib.h>
  20
  21         void *malloc_align (
  22
  23 /*  SYNOPSIS */
  24         size_t size,
  25         size_t alignment)
  26
  27 /*  FUNCTION
  28         Allocate aligned memory.
  29
  30     INPUTS
  31         size - How much memory to allocate.
  32         alignment - Alignment of allocated memory. The address of the
  33                     allocated memory will be a multiple of this value, which
  34                     must be a power of two and a multiple of sizeof(void *).
  35
  36     RESULT
  37         A pointer to the allocated memory or NULL.
  38
  39     NOTES
  40         errno is set to EINVAL if the alignment parameter was not a power of
  41         two, or was not a multiple of sizeof(void *).
  42         errno is set to ENOMEM if there was insufficient memory to fulfill
  43         the request.
  44         Memory allocated by malloc_align() should be freed with free(). If
  45         not, it will be freed when the program terminates.
  46
  47         This function is AROS specific.
  48
  49     EXAMPLE
  50
  51     BUGS
  52
  53     SEE ALSO
  54         calloc(), free(), malloc()
  55
  56     INTERNALS
  57
  58 ******************************************************************************/
  59 {
  60     char *mem = NULL, *orig, *tmp;
  61
  62     /* check the alignment is valid */
  63     if (alignment % sizeof(void *) != 0 || !powerof2(alignment))
  64     {
  65         errno = EINVAL;
  66         return NULL;
  67     }
  68
  69     /* allocate enough space to satisfy the alignment and save some info */
  70     mem = malloc(size + alignment + AROS_ALIGN(sizeof(size_t)) + AROS_ALIGN(sizeof(void *)));
  71     if (mem == NULL)
  72     {
  73         errno = ENOMEM;
  74         return NULL;
  75     }
  76
  77     /* if it's already aligned correctly, then we just use it as-is */
  78     if (((IPTR) mem & (alignment-1)) == 0)
  79         return mem;
  80
  81     orig = mem;
  82
  83     /* move forward to an even alignment boundary */
  84     mem = (char *) (((IPTR) mem + alignment - 1) & -alignment);
  85     tmp = mem;
  86
  87     /* store a magic number in the place that free() will look for the
  88      * allocation size, so it can handle this specially */
  89     tmp -= AROS_ALIGN(sizeof(size_t *));
  90     *((size_t *) tmp) = MEMALIGN_MAGIC;
  91
  92     /* then store the original pointer before it, for free() to find */
  93     tmp -= sizeof(void *);
  94     *((void **) tmp) = orig;
  95
  96     return mem;
  97 } /* posix_memalign */