firmware/libc/strncmp.c

   1 /*
   2 FUNCTION
   3         <<strncmp>>---character string compare
   4
   5 INDEX
   6         strncmp
   7
   8 ANSI_SYNOPSIS
   9         #include <string.h>
  10         int strncmp(const char *<[a]>, const char * <[b]>, size_t <[length]>);
  11
  12 TRAD_SYNOPSIS
  13         #include <string.h>
  14         int strncmp(<[a]>, <[b]>, <[length]>)
  15         char *<[a]>;
  16         char *<[b]>;
  17         size_t <[length]>
  18
  19 DESCRIPTION
  20         <<strncmp>> compares up to <[length]> characters
  21         from the string at <[a]> to the string at <[b]>.
  22
  23 RETURNS
  24         If <<*<[a]>>> sorts lexicographically after <<*<[b]>>>,
  25         <<strncmp>> returns a number greater than zero.  If the two
  26         strings are equivalent, <<strncmp>> returns zero.  If <<*<[a]>>>
  27         sorts lexicographically before <<*<[b]>>>, <<strncmp>> returns a
  28         number less than zero.
  29
  30 PORTABILITY
  31 <<strncmp>> is ANSI C.
  32
  33 <<strncmp>> requires no supporting OS subroutines.
  34
  35 QUICKREF
  36         strncmp ansi pure
  37 */
  38
  39 #include <string.h>
  40 #include <limits.h>
  41 #include "_ansi.h" /* for _DEFUN */
  42
  43 /* Nonzero if either X or Y is not aligned on a "long" boundary.  */
  44 #define UNALIGNED(X, Y) \
  45   (((long)X & (sizeof (long) - 1)) | ((long)Y & (sizeof (long) - 1)))
  46
  47 /* DETECTNULL returns nonzero if (long)X contains a NULL byte. */
  48 #if LONG_MAX == 2147483647L
  49 #define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080)
  50 #else
  51 #if LONG_MAX == 9223372036854775807L
  52 #define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080)
  53 #else
  54 #error long int is not a 32bit or 64bit type.
  55 #endif
  56 #endif
  57
  58 #ifndef DETECTNULL
  59 #error long int is not a 32bit or 64bit byte
  60 #endif
  61
  62 int
  63 _DEFUN (strncmp, (s1, s2, n),
  64         _CONST char *s1 _AND
  65         _CONST char *s2 _AND
  66         size_t n)
  67 {
  68 #if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
  69   if (n == 0)
  70     return 0;
  71
  72   while (n-- != 0 && *s1 == *s2)
  73     {
  74       if (n == 0 || *s1 == '\0')
  75         break;
  76       s1++;
  77       s2++;
  78     }
  79
  80   return (*(unsigned char *) s1) - (*(unsigned char *) s2);
  81 #else
  82   unsigned long *a1;
  83   unsigned long *a2;
  84
  85   if (n == 0)
  86     return 0;
  87
  88   /* If s1 or s2 are unaligned, then compare bytes. */
  89   if (!UNALIGNED (s1, s2))
  90     {
  91       /* If s1 and s2 are word-aligned, compare them a word at a time. */
  92       a1 = (unsigned long*)s1;
  93       a2 = (unsigned long*)s2;
  94       while (n >= sizeof (long) && *a1 == *a2)
  95         {
  96           n -= sizeof (long);
  97
  98           /* If we've run out of bytes or hit a null, return zero
  99              since we already know *a1 == *a2.  */
 100           if (n == 0 || DETECTNULL (*a1))
 101             return 0;
 102
 103           a1++;
 104           a2++;
 105         }
 106
 107       /* A difference was detected in last few bytes of s1, so search bytewise */
 108       s1 = (char*)a1;
 109       s2 = (char*)a2;
 110     }
 111
 112   while (n-- > 0 && *s1 == *s2)
 113     {
 114       /* If we've run out of bytes or hit a null, return zero
 115          since we already know *s1 == *s2.  */
 116       if (n == 0 || *s1 == '\0')
 117         return 0;
 118       s1++;
 119       s2++;
 120     }
 121   return (*(unsigned char *) s1) - (*(unsigned char *) s2);
 122 #endif /* not PREFER_SIZE_OVER_SPEED */
 123 }