firmware/common/memchr.c

   1 /*
   2 FUNCTION
   3         <<memchr>>---search for character in memory
   4
   5 INDEX
   6         memchr
   7
   8 ANSI_SYNOPSIS
   9         #include <string.h>
  10         void * memchr(const void *<[s1]>, int <[c]>, size_t <[n]>);
  11
  12 TRAD_SYNOPSIS
  13         #include <string.h>
  14         void * memchr(<[s1]>, <[c]>, <[n]>);
  15         void *<[string]>;
  16         int *<[c]>;
  17         size_t *<[n]>;
  18
  19 DESCRIPTION
  20         This function scans the first <[n]> bytes of the memory pointed
  21         to by <[s1]> for the character <[c]> (converted to a char).
  22
  23 RETURNS
  24         Returns a pointer to the matching byte, or a null pointer if
  25         <[c]> does not occur in <[s1]>.
  26
  27 PORTABILITY
  28 <<memchr>> is ANSI C.
  29
  30 <<memchr>> requires no supporting OS subroutines.
  31
  32 QUICKREF
  33         memchr ansi pure
  34 */
  35
  36 #include <string.h>
  37 #include <limits.h>
  38
  39 /* Nonzero if X is not aligned on a "long" boundary.  */
  40 #define UNALIGNED(X) ((long)X & (sizeof (long) - 1))
  41
  42 /* How many bytes are loaded each iteration of the word copy loop.  */
  43 #define LBLOCKSIZE (sizeof (long))
  44
  45 #if LONG_MAX == 2147483647L
  46 #define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080)
  47 #else
  48 #if LONG_MAX == 9223372036854775807L
  49 /* Nonzero if X (a long int) contains a NULL byte. */
  50 #define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080)
  51 #else
  52 #error long int is not a 32bit or 64bit type.
  53 #endif
  54 #endif
  55
  56 /* DETECTCHAR returns nonzero if (long)X contains the byte used
  57    to fill (long)MASK. */
  58 #define DETECTCHAR(X,MASK) (DETECTNULL(X ^ MASK))
  59
  60 void *
  61 _DEFUN (memchr, (s1, i, n),
  62         _CONST void *s1 _AND
  63         int i _AND size_t n)
  64 {
  65   _CONST unsigned char *s = (_CONST unsigned char *)s1;
  66 #if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
  67   unsigned char c = (unsigned char)i;
  68
  69   while (n-- > 0)
  70     {
  71       if (*s == c)
  72         {
  73           return (void *)s;
  74         }
  75       s++;
  76     }
  77
  78   return NULL;
  79 #else
  80   unsigned char c = (unsigned char)i;
  81   unsigned long mask,j;
  82   unsigned long *aligned_addr;
  83
  84   if (!UNALIGNED (s))
  85     {
  86       mask = 0;
  87       for (j = 0; j < LBLOCKSIZE; j++)
  88         mask = (mask << 8) | c;
  89
  90       aligned_addr = (unsigned long*)s;
  91       while ((!DETECTCHAR (*aligned_addr, mask)) && (n>LBLOCKSIZE))
  92         {
  93           aligned_addr++;
  94           n -= LBLOCKSIZE;
  95         }
  96
  97       /* The block of bytes currently pointed to by aligned_addr
  98          may contain the target character or there may be less than
  99          LBLOCKSIZE bytes left to search. We check the last few
 100          bytes using the bytewise search.  */
 101
 102       s = (unsigned char*)aligned_addr;
 103     }
 104
 105   while (n-- > 0)
 106     {
 107       if (*s == c)
 108         {
 109           return (void *)s;
 110         }
 111       s++;
 112     }
 113
 114   return NULL;
 115 #endif /* not PREFER_SIZE_OVER_SPEED */
 116 }