bitmath.c

在x86平台上运行不可信任代码的sandbox。

/* libFLAC - Free Lossless Audio Codec library
 * Copyright (C) 2001,2002,2003,2004,2005  Josh Coalson
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *
 * - Redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution.
 *
 * - Neither the name of the Xiph.org Foundation nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "private/bitmath.h"
#include "FLAC/assert.h"

/* An example of what FLAC__bitmath_ilog2() computes:
 *
 * ilog2( 0) = assertion failure
 * ilog2( 1) = 0
 * ilog2( 2) = 1
 * ilog2( 3) = 1
 * ilog2( 4) = 2
 * ilog2( 5) = 2
 * ilog2( 6) = 2
 * ilog2( 7) = 2
 * ilog2( 8) = 3
 * ilog2( 9) = 3
 * ilog2(10) = 3
 * ilog2(11) = 3
 * ilog2(12) = 3
 * ilog2(13) = 3
 * ilog2(14) = 3
 * ilog2(15) = 3
 * ilog2(16) = 4
 * ilog2(17) = 4
 * ilog2(18) = 4
 */
unsigned FLAC__bitmath_ilog2(FLAC__uint32 v)
{
	unsigned l = 0;
	FLAC__ASSERT(v > 0);
	while(v >>= 1)
		l++;
	return l;
}

unsigned FLAC__bitmath_ilog2_wide(FLAC__uint64 v)
{
	unsigned l = 0;
	FLAC__ASSERT(v > 0);
	while(v >>= 1)
		l++;
	return l;
}

/* An example of what FLAC__bitmath_silog2() computes:
 *
 * silog2(-10) = 5
 * silog2(- 9) = 5
 * silog2(- 8) = 4
 * silog2(- 7) = 4
 * silog2(- 6) = 4
 * silog2(- 5) = 4
 * silog2(- 4) = 3
 * silog2(- 3) = 3
 * silog2(- 2) = 2
 * silog2(- 1) = 2
 * silog2(  0) = 0
 * silog2(  1) = 2
 * silog2(  2) = 3
 * silog2(  3) = 3
 * silog2(  4) = 4
 * silog2(  5) = 4
 * silog2(  6) = 4
 * silog2(  7) = 4
 * silog2(  8) = 5
 * silog2(  9) = 5
 * silog2( 10) = 5
 */
unsigned FLAC__bitmath_silog2(int v)
{
	while(1) {
		if(v == 0) {
			return 0;
		}
		else if(v > 0) {
			unsigned l = 0;
			while(v) {
				l++;
				v >>= 1;
			}
			return l+1;
		}
		else if(v == -1) {
			return 2;
		}
		else {
			v++;
			v = -v;
		}
	}
}

unsigned FLAC__bitmath_silog2_wide(FLAC__int64 v)
{
	while(1) {
		if(v == 0) {
			return 0;
		}
		else if(v > 0) {
			unsigned l = 0;
			while(v) {
				l++;
				v >>= 1;
			}
			return l+1;
		}
		else if(v == -1) {
			return 2;
		}
		else {
			v++;
			v = -v;
		}
	}
}