libc-top-half/musl/src/malloc/calloc.c

   1 #include <stdlib.h>
   2 #include <stdint.h>
   3 #include <string.h>
   4 #include <errno.h>
   5 #include "dynlink.h"
   6
   7 static size_t mal0_clear(char *p, size_t n)
   8 {
   9         const size_t pagesz = 4096; /* arbitrary */
  10         if (n < pagesz) return n;
  11 #ifdef __GNUC__
  12         typedef uint64_t __attribute__((__may_alias__)) T;
  13 #else
  14         typedef unsigned char T;
  15 #endif
  16         char *pp = p + n;
  17         size_t i = (uintptr_t)pp & (pagesz - 1);
  18         for (;;) {
  19                 pp = memset(pp - i, 0, i);
  20                 if (pp - p < pagesz) return pp - p;
  21                 for (i = pagesz; i; i -= 2*sizeof(T), pp -= 2*sizeof(T))
  22                         if (((T *)pp)[-1] | ((T *)pp)[-2])
  23                                 break;
  24         }
  25 }
  26
  27 static int allzerop(void *p)
  28 {
  29         return 0;
  30 }
  31 weak_alias(allzerop, __malloc_allzerop);
  32
  33 void *calloc(size_t m, size_t n)
  34 {
  35         if (n && m > (size_t)-1/n) {
  36                 errno = ENOMEM;
  37                 return 0;
  38         }
  39         n *= m;
  40         void *p = malloc(n);
  41         if (!p || (!__malloc_replaced && __malloc_allzerop(p)))
  42                 return p;
  43         n = mal0_clear(p, n);
  44         return memset(p, 0, n);
  45 }