bitops.h

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/* Copyright (C) 2001-2007 Peter Selinger.
   This file is part of Potrace. It is free software and it is covered
   by the GNU General Public License. See the file COPYING for details. */

/* $Id: bitops.h 147 2007-04-09 00:44:09Z selinger $ */

/* bits.h: this file defines some macros for bit manipulations. We
   provide a generic implementation, as well as machine- and
   compiler-specific fast implementations */

/* lobit: return the position of the rightmost "1" bit of an int, or
   32 if none. hibit: return 1 + the position of the leftmost "1" bit
   of an int, or 0 if none. Note: these functions work on 32-bit
   integers. */

#ifndef BITOPS_H
#define BITOPS_H

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

/* ---------------------------------------------------------------------- */
/* machine specific macros */

#if defined(HAVE_I386)

static inline unsigned int lobit(unsigned int x) {
  unsigned int res;
  asm ("bsf     %1,%0\n\t"
       "jnz     0f\n\t"
       "movl    $32,%0\n"
       "0:"
       : "=r" (res)
       : "r" (x));
  return res;
}

static inline unsigned int hibit(unsigned int x) {
  unsigned int res;                                     

  asm ("bsr     %1,%0\n\t"
       "jnz     0f\n\t"
       "movl    $-1,%0\n"
       "0:"
       : "=r" (res)
       : "r" (x));
  return res+1;
}

/* ---------------------------------------------------------------------- */
#else /* generic macros */

static inline unsigned int lobit(unsigned int x) {
  unsigned int res = 32;
  while (x & 0xffffff) {
    x <<= 8;
    res -= 8;
  }
  while (x) {
    x <<= 1;
    res -= 1;
  }
  return res;
}

static inline unsigned int hibit(unsigned int x) {
  unsigned int res = 0;
  while (x > 0xff) {
    x >>= 8;
    res += 8;
  }
  while (x) {
    x >>= 1;
    res += 1;
  }
  return res;
}

#endif 

#endif /* BITOPS_H */