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  1. /*
  2. FUNCTION
  3.         <<rawmemchr>>---find character in memory
  4.  
  5. INDEX
  6.         rawmemchr
  7.  
  8. ANSI_SYNOPSIS
  9.         #include <string.h>
  10.         void *rawmemchr(const void *<[src]>, int <[c]>);
  11.  
  12. TRAD_SYNOPSIS
  13.         #include <string.h>
  14.         void *rawmemchr(<[src]>, <[c]>)
  15.         void *<[src]>;
  16.         void *<[c]>;
  17.  
  18. DESCRIPTION
  19.         This function searches memory starting at <<*<[src]>>> for the
  20.         character <[c]>.  The search only ends with the first occurrence
  21.         of <[c]>; in particular, <<NUL>> does not terminate the search.
  22.         No bounds checking is performed, so this function should only
  23.         be used when it is certain that the character <[c]> will be found.
  24.  
  25. RETURNS
  26.         A pointer to the first occurance of character <[c]>.
  27.  
  28. PORTABILITY
  29. <<rawmemchr>> is a GNU extension.
  30.  
  31. <<rawmemchr>> requires no supporting OS subroutines.
  32.  
  33. QUICKREF
  34.         rawmemchr
  35. */
  36.  
  37. #include <_ansi.h>
  38. #include <string.h>
  39. #include <limits.h>
  40.  
  41. /* Nonzero if X is not aligned on a "long" boundary.  */
  42. #define UNALIGNED(X) ((long)X & (sizeof (long) - 1))
  43.  
  44. /* How many bytes are loaded each iteration of the word copy loop.  */
  45. #define LBLOCKSIZE (sizeof (long))
  46.  
  47. /* Threshhold for punting to the bytewise iterator.  */
  48. #define TOO_SMALL(LEN)  ((LEN) < LBLOCKSIZE)
  49.  
  50. #if LONG_MAX == 2147483647L
  51. #define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080)
  52. #else
  53. #if LONG_MAX == 9223372036854775807L
  54. /* Nonzero if X (a long int) contains a NULL byte. */
  55. #define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080)
  56. #else
  57. #error long int is not a 32bit or 64bit type.
  58. #endif
  59. #endif
  60.  
  61. #ifndef DETECTNULL
  62. #error long int is not a 32bit or 64bit byte
  63. #endif
  64.  
  65. /* DETECTCHAR returns nonzero if (long)X contains the byte used
  66.    to fill (long)MASK. */
  67. #define DETECTCHAR(X,MASK) (DETECTNULL(X ^ MASK))
  68.  
  69. _PTR
  70. _DEFUN (rawmemchr, (src_void, c),
  71.         _CONST _PTR src_void _AND
  72.         int c)
  73. {
  74.   _CONST unsigned char *src = (_CONST unsigned char *) src_void;
  75.   unsigned char d = c;
  76.  
  77. #if !defined(PREFER_SIZE_OVER_SPEED) && !defined(__OPTIMIZE_SIZE__)
  78.   unsigned long *asrc;
  79.   unsigned long  mask;
  80.   unsigned int i;
  81.  
  82.   while (UNALIGNED (src))
  83.     {
  84.       if (*src == d)
  85.         return (void *) src;
  86.       src++;
  87.     }
  88.  
  89.   /* If we get this far, we know that src is word-aligned. */
  90.   /* The fast code reads the source one word at a time and only
  91.      performs the bytewise search on word-sized segments if they
  92.      contain the search character, which is detected by XORing
  93.      the word-sized segment with a word-sized block of the search
  94.      character and then detecting for the presence of NUL in the
  95.      result.  */
  96.   asrc = (unsigned long *) src;
  97.   mask = d << 8 | d;
  98.   mask = mask << 16 | mask;
  99.   for (i = 32; i < LBLOCKSIZE * 8; i <<= 1)
  100.     mask = (mask << i) | mask;
  101.  
  102.   while (1)
  103.     {
  104.       if (DETECTCHAR (*asrc, mask))
  105.         break;
  106.       asrc++;
  107.     }
  108.  
  109.   /* We have the matching word, now we resort to a bytewise loop. */
  110.  
  111.   src = (unsigned char *) asrc;
  112.  
  113. #endif /* !PREFER_SIZE_OVER_SPEED && !__OPTIMIZE_SIZE__ */
  114.  
  115.   while (1)
  116.     {
  117.       if (*src == d)
  118.         return (void *) src;
  119.       src++;
  120.     }
  121. }
  122.