newlib/libc/string/strcmp.c

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