newlib/libc/string/rawmemchr.c

   1 /*
   2 FUNCTION
   3         <<rawmemchr>>---find character in memory
   4
   5 INDEX
   6         rawmemchr
   7
   8 SYNOPSIS
   9         #include <string.h>
  10         void *rawmemchr(const void *<[src]>, int <[c]>);
  11
  12 DESCRIPTION
  13         This function searches memory starting at <<*<[src]>>> for the
  14         character <[c]>.  The search only ends with the first occurrence
  15         of <[c]>; in particular, <<NUL>> does not terminate the search.
  16         No bounds checking is performed, so this function should only
  17         be used when it is certain that the character <[c]> will be found.
  18
  19 RETURNS
  20         A pointer to the first occurance of character <[c]>.
  21
  22 PORTABILITY
  23 <<rawmemchr>> is a GNU extension.
  24
  25 <<rawmemchr>> requires no supporting OS subroutines.
  26
  27 QUICKREF
  28         rawmemchr
  29 */
  30
  31 #include <_ansi.h>
  32 #include <string.h>
  33 #include <limits.h>
  34
  35 /* Nonzero if X is not aligned on a "long" boundary.  */
  36 #define UNALIGNED(X) ((long)X & (sizeof (long) - 1))
  37
  38 /* How many bytes are loaded each iteration of the word copy loop.  */
  39 #define LBLOCKSIZE (sizeof (long))
  40
  41 /* Threshhold for punting to the bytewise iterator.  */
  42 #define TOO_SMALL(LEN)  ((LEN) < LBLOCKSIZE)
  43
  44 #if LONG_MAX == 2147483647L
  45 #define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080)
  46 #else
  47 #if LONG_MAX == 9223372036854775807L
  48 /* Nonzero if X (a long int) contains a NULL byte. */
  49 #define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080)
  50 #else
  51 #error long int is not a 32bit or 64bit type.
  52 #endif
  53 #endif
  54
  55 #ifndef DETECTNULL
  56 #error long int is not a 32bit or 64bit byte
  57 #endif
  58
  59 /* DETECTCHAR returns nonzero if (long)X contains the byte used
  60    to fill (long)MASK. */
  61 #define DETECTCHAR(X,MASK) (DETECTNULL(X ^ MASK))
  62
  63 void *
  64 rawmemchr (const void *src_void,
  65         int c)
  66 {
  67   const unsigned char *src = (const unsigned char *) src_void;
  68   unsigned char d = c;
  69
  70 #if !defined(PREFER_SIZE_OVER_SPEED) && !defined(__OPTIMIZE_SIZE__)
  71   unsigned long *asrc;
  72   unsigned long  mask;
  73   unsigned int i;
  74
  75   while (UNALIGNED (src))
  76     {
  77       if (*src == d)
  78         return (void *) src;
  79       src++;
  80     }
  81
  82   /* If we get this far, we know that src is word-aligned. */
  83   /* The fast code reads the source one word at a time and only
  84      performs the bytewise search on word-sized segments if they
  85      contain the search character, which is detected by XORing
  86      the word-sized segment with a word-sized block of the search
  87      character and then detecting for the presence of NUL in the
  88      result.  */
  89   asrc = (unsigned long *) src;
  90   mask = d << 8 | d;
  91   mask = mask << 16 | mask;
  92   for (i = 32; i < LBLOCKSIZE * 8; i <<= 1)
  93     mask = (mask << i) | mask;
  94
  95   while (1)
  96     {
  97       if (DETECTCHAR (*asrc, mask))
  98         break;
  99       asrc++;
 100     }
 101
 102   /* We have the matching word, now we resort to a bytewise loop. */
 103
 104   src = (unsigned char *) asrc;
 105
 106 #endif /* !PREFER_SIZE_OVER_SPEED && !__OPTIMIZE_SIZE__ */
 107
 108   while (1)
 109     {
 110       if (*src == d)
 111         return (void *) src;
 112       src++;
 113     }
 114 }