src/malloc/memalign.c

   1 #include <stdlib.h>
   2 #include <stdint.h>
   3 #include <errno.h>
   4 #include "libc.h"
   5
   6 /* This function should work with most dlmalloc-like chunk bookkeeping
   7  * systems, but it's only guaranteed to work with the native implementation
   8  * used in this library. */
   9
  10 void *__memalign(size_t align, size_t len)
  11 {
  12         unsigned char *mem, *new, *end;
  13         size_t header, footer;
  14
  15         if ((align & -align) != align) {
  16                 errno = EINVAL;
  17                 return NULL;
  18         }
  19
  20         if (len > SIZE_MAX - align) {
  21                 errno = ENOMEM;
  22                 return NULL;
  23         }
  24
  25         if (align <= 4*sizeof(size_t)) {
  26                 if (!(mem = malloc(len)))
  27                         return NULL;
  28                 return mem;
  29         }
  30
  31         if (!(mem = malloc(len + align-1)))
  32                 return NULL;
  33
  34         new = (void *)((uintptr_t)mem + align-1 & -align);
  35         if (new == mem) return mem;
  36
  37         header = ((size_t *)mem)[-1];
  38
  39         if (!(header & 7)) {
  40                 ((size_t *)new)[-2] = ((size_t *)mem)[-2] + (new-mem);
  41                 ((size_t *)new)[-1] = ((size_t *)mem)[-1] - (new-mem);
  42                 return new;
  43         }
  44
  45         end = mem + (header & -8);
  46         footer = ((size_t *)end)[-2];
  47
  48         ((size_t *)mem)[-1] = header&7 | new-mem;
  49         ((size_t *)new)[-2] = footer&7 | new-mem;
  50         ((size_t *)new)[-1] = header&7 | end-new;
  51         ((size_t *)end)[-2] = footer&7 | end-new;
  52
  53         if (new != mem) free(mem);
  54         return new;
  55 }
  56
  57 weak_alias(__memalign, memalign);