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/*

FUNCTION

        <<strncmp>>---character string compare

INDEX

        strncmp

ANSI_SYNOPSIS

        #include <string.h>

        int strncmp(const char *<[a]>, const char * <[b]>, size_t <[length]>);

TRAD_SYNOPSIS

        #include <string.h>

        int strncmp(<[a]>, <[b]>, <[length]>)

        char *<[a]>;

        char *<[b]>;

        size_t <[length]>

DESCRIPTION

        <<strncmp>> compares up to <[length]> characters

        from the string at <[a]> to the string at <[b]>.

RETURNS

        If <<*<[a]>>> sorts lexicographically after <<*<[b]>>>,

        <<strncmp>> returns a number greater than zero.  If the two

        strings are equivalent, <<strncmp>> returns zero.  If <<*<[a]>>>

        sorts lexicographically before <<*<[b]>>>, <<strncmp>> returns a

        number less than zero.

PORTABILITY

<<strncmp>> is ANSI C.

<<strncmp>> requires no supporting OS subroutines.

QUICKREF

        strncmp ansi pure

*/

#include <string.h>

#include <limits.h>

/* Nonzero if either X or Y is not aligned on a "long" boundary.  */

#define UNALIGNED(X, Y) \

  (((long)X & (sizeof (long) - 1)) | ((long)Y & (sizeof (long) - 1)))

/* DETECTNULL returns nonzero if (long)X contains a NULL byte. */

#if LONG_MAX == 2147483647L

#define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080)

#else

#if LONG_MAX == 9223372036854775807L

#define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080)

#else

#error long int is not a 32bit or 64bit type.

#endif

#endif

#ifndef DETECTNULL

#error long int is not a 32bit or 64bit byte

#endif

int

_DEFUN (strncmp, (s1, s2, n),

        _CONST char *s1 _AND

        _CONST char *s2 _AND

        size_t n)

{

#if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)

  if (n == 0)

    return 0;

  while (n-- != 0 && *s1 == *s2)

    {

      if (n == 0 || *s1 == '\0')

        break;

      s1++;

      s2++;

    }

  return (*(unsigned char *) s1) - (*(unsigned char *) s2);

#else

  unsigned long *a1;

  unsigned long *a2;

  if (n == 0)

    return 0;

  /* If s1 or s2 are unaligned, then compare bytes. */

  if (!UNALIGNED (s1, s2))

    {

      /* If s1 and s2 are word-aligned, compare them a word at a time. */

      a1 = (unsigned long*)s1;

      a2 = (unsigned long*)s2;

      while (n >= sizeof (long) && *a1 == *a2)

        {

          n -= sizeof (long);

          /* If we've run out of bytes or hit a null, return zero

             since we already know *a1 == *a2.  */

          if (n == 0 || DETECTNULL (*a1))

            return 0;

          a1++;

          a2++;

        }

      /* A difference was detected in last few bytes of s1, so search bytewise */

      s1 = (char*)a1;

      s2 = (char*)a2;

    }

  while (n-- > 0 && *s1 == *s2)

    {

      /* If we've run out of bytes or hit a null, return zero

         since we already know *s1 == *s2.  */

      if (n == 0 || *s1 == '\0')

        return 0;

      s1++;

      s2++;

    }

  return (*(unsigned char *) s1) - (*(unsigned char *) s2);

#endif /* not PREFER_SIZE_OVER_SPEED */

}