firmware/libc/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 #include "_ansi.h" /* for _DEFUN */
  39
  40 /* Nonzero if X is not aligned on a "long" boundary.  */
  41 #define UNALIGNED(X) ((long)X & (sizeof (long) - 1))
  42
  43 /* How many bytes are loaded each iteration of the word copy loop.  */
  44 #define LBLOCKSIZE (sizeof (long))
  45
  46 #if LONG_MAX == 2147483647L
  47 #define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080)
  48 #else
  49 #if LONG_MAX == 9223372036854775807L
  50 /* Nonzero if X (a long int) contains a NULL byte. */
  51 #define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080)
  52 #else
  53 #error long int is not a 32bit or 64bit type.
  54 #endif
  55 #endif
  56
  57 /* DETECTCHAR returns nonzero if (long)X contains the byte used
  58    to fill (long)MASK. */
  59 #define DETECTCHAR(X,MASK) (DETECTNULL(X ^ MASK))
  60
  61 void *
  62 _DEFUN (memchr, (s1, i, n),
  63         _CONST void *s1 _AND
  64         int i _AND size_t n)
  65 {
  66   _CONST unsigned char *s = (_CONST unsigned char *)s1;
  67 #if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
  68   unsigned char c = (unsigned char)i;
  69
  70   while (n-- > 0)
  71     {
  72       if (*s == c)
  73         {
  74           return (void *)s;
  75         }
  76       s++;
  77     }
  78
  79   return NULL;
  80 #else
  81   unsigned char c = (unsigned char)i;
  82   unsigned long mask,j;
  83   unsigned long *aligned_addr;
  84
  85   if (!UNALIGNED (s))
  86     {
  87       mask = 0;
  88       for (j = 0; j < LBLOCKSIZE; j++)
  89         mask = (mask << 8) | c;
  90
  91       aligned_addr = (unsigned long*)s;
  92       while ((!DETECTCHAR (*aligned_addr, mask)) && (n>LBLOCKSIZE))
  93         {
  94           aligned_addr++;
  95           n -= LBLOCKSIZE;
  96         }
  97
  98       /* The block of bytes currently pointed to by aligned_addr
  99          may contain the target character or there may be less than
 100          LBLOCKSIZE bytes left to search. We check the last few
 101          bytes using the bytewise search.  */
 102
 103       s = (unsigned char*)aligned_addr;
 104     }
 105
 106   while (n-- > 0)
 107     {
 108       if (*s == c)
 109         {
 110           return (void *)s;
 111         }
 112       s++;
 113     }
 114
 115   return NULL;
 116 #endif /* not PREFER_SIZE_OVER_SPEED */
 117 }