toolchain/gcc/newlib/libc/string/memcmp.c

   1 /*
   2 FUNCTION
   3         <<memcmp>>---compare two memory areas
   4
   5 INDEX
   6         memcmp
   7
   8 ANSI_SYNOPSIS
   9         #include <string.h>
  10         int memcmp(const void *<[s1]>, const void *<[s2]>, size_t <[n]>);
  11
  12 TRAD_SYNOPSIS
  13         #include <string.h>
  14         int memcmp(<[s1]>, <[s2]>, <[n]>)
  15         void *<[s1]>;
  16         void *<[s2]>;
  17         size_t <[n]>;
  18
  19 DESCRIPTION
  20         This function compares not more than <[n]> characters of the
  21         object pointed to by <[s1]> with the object pointed to by <[s2]>.
  22
  23
  24 RETURNS
  25         The function returns an integer greater than, equal to or
  26         less than zero  according to whether the object pointed to by
  27         <[s1]> is greater than, equal to or less than the object
  28         pointed to by <[s2]>.
  29
  30 PORTABILITY
  31 <<memcmp>> is ANSI C.
  32
  33 <<memcmp>> requires no supporting OS subroutines.
  34
  35 QUICKREF
  36         memcmp ansi pure
  37 */
  38
  39 #include <string.h>
  40
  41
  42 /* Nonzero if either X or Y is not aligned on a "long" boundary.  */
  43 #define UNALIGNED(X, Y) \
  44   (((long)X & (sizeof (long) - 1)) | ((long)Y & (sizeof (long) - 1)))
  45
  46 /* How many bytes are copied each iteration of the word copy loop.  */
  47 #define LBLOCKSIZE (sizeof (long))
  48
  49 /* Threshhold for punting to the byte copier.  */
  50 #define TOO_SMALL(LEN)  ((LEN) < LBLOCKSIZE)
  51
  52 int
  53 _DEFUN (memcmp, (m1, m2, n),
  54         _CONST _PTR m1 _AND
  55         _CONST _PTR m2 _AND
  56         size_t n)
  57 {
  58 #if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
  59   unsigned char *s1 = (unsigned char *) m1;
  60   unsigned char *s2 = (unsigned char *) m2;
  61
  62   while (n--)
  63     {
  64       if (*s1 != *s2)
  65         {
  66           return *s1 - *s2;
  67         }
  68       s1++;
  69       s2++;
  70     }
  71   return 0;
  72 #else
  73   unsigned char *s1 = (unsigned char *) m1;
  74   unsigned char *s2 = (unsigned char *) m2;
  75   unsigned long *a1;
  76   unsigned long *a2;
  77
  78   /* If the size is too small, or either pointer is unaligned,
  79      then we punt to the byte compare loop.  Hopefully this will
  80      not turn up in inner loops.  */
  81   if (!TOO_SMALL(n) && !UNALIGNED(s1,s2))
  82     {
  83       /* Otherwise, load and compare the blocks of memory one
  84          word at a time.  */
  85       a1 = (unsigned long*) s1;
  86       a2 = (unsigned long*) s2;
  87       while (n >= LBLOCKSIZE)
  88         {
  89           if (*a1 != *a2)
  90             break;
  91           a1++;
  92           a2++;
  93           n -= LBLOCKSIZE;
  94         }
  95
  96       /* check m mod LBLOCKSIZE remaining characters */
  97
  98       s1 = (char*)a1;
  99       s2 = (char*)a2;
 100     }
 101
 102   while (n--)
 103     {
 104       if (*s1 != *s2)
 105         return *s1 - *s2;
 106       s1++;
 107       s2++;
 108     }
 109
 110   return 0;
 111 #endif /* not PREFER_SIZE_OVER_SPEED */
 112 }
 113