x15/kern/log2.h

/*
 * Copyright (c) 2014 Richard Braun.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 *
 * Integer base 2 logarithm operations.
 */

#ifndef KERN_LOG2_H
#define KERN_LOG2_H

#include <assert.h>
#include <limits.h>

/*
 * Return the base-2 logarithm of the given value, or of the first
 * power-of-two below the given value if it's not a power-of-two.
 */
static inline unsigned int
log2 (unsigned long x)
{
  assert (x != 0);
  return (LONG_BIT - __builtin_clzl (x) - 1);
}

/*
 * Return the base-2 logarithm of the given value, or of the first
 * power-of-two above the given value if it's not a power-of-two.
 */
static inline unsigned int
log2_order (unsigned long size)
{
  assert (size != 0);
  return (size == 1 ? 0 : (log2 (size - 1) + 1));
}

#endif