newlib/libc/string/memcmp.c

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