Function strncmp

rEFIt_UEFI/Platform/Posix/string.cpp:73–114

faster implementation than AsciiStrnCmp. AsciiStrnCmp calls AsciiStrSize 4 times. int strncmp( const char * s1, const char * s2, size_t n ) { while ( n && *s1 && ( *s1 == *s2 ) ) { ++s1; ++s2; --n; } if ( n == 0 ) { return 0; } else { return ( *(unsigned char *)s1 - *(unsigned char *)s2 ); } } Compare no more than N characters of S1 and S2, returning less than, equal to or greater than zero

   if S1 is lexicographically less than, equal to or
   greater than S2.  */
int
strncmp(const char *s1, const char *s2, size_t n)
{
  unsigned char c1 = '\0';
  unsigned char c2 = '\0';

  if (n >= 4)
    {
      size_t n4 = n >> 2;
      do
        {
          c1 = (unsigned char) *s1++;
          c2 = (unsigned char) *s2++;
          if (c1 == '\0' || c1 != c2)
            return c1 - c2;
          c1 = (unsigned char) *s1++;
          c2 = (unsigned char) *s2++;
          if (c1 == '\0' || c1 != c2)
            return c1 - c2;
          c1 = (unsigned char) *s1++;
          c2 = (unsigned char) *s2++;
          if (c1 == '\0' || c1 != c2)
            return c1 - c2;
          c1 = (unsigned char) *s1++;
          c2 = (unsigned char) *s2++;
          if (c1 == '\0' || c1 != c2)
            return c1 - c2;
        } while (--n4 > 0);
      n &= 3;
    }

  while (n > 0)
    {
      c1 = (unsigned char) *s1++;
      c2 = (unsigned char) *s2++;
      if (c1 == '\0' || c1 != c2)
        return c1 - c2;
      n--;
    }

  return c1 - c2;
}