fixed.c

tcpmp.src.0.72RC1 优秀的多媒体播放器TCPMP的源代码

/* libFLAC - Free Lossless Audio Codec library
 * Copyright (C) 2000,2001,2002,2003,2004,2005  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 <math.h>
#include "private/bitmath.h"
#include "private/fixed.h"
#include "FLAC/assert.h"

#ifndef M_LN2
/* math.h in VC++ doesn't seem to have this (how Microsoft is that?) */
#define M_LN2 0.69314718055994530942
#endif

#ifdef min
#undef min
#endif
#define min(x,y) ((x) < (y)? (x) : (y))

#ifdef local_abs
#undef local_abs
#endif
#define local_abs(x) ((unsigned)((x)<0? -(x) : (x)))

#ifdef FLAC__INTEGER_ONLY_LIBRARY
/* rbps stands for residual bits per sample
 *
 *             (ln(2) * err)
 * rbps = log  (-----------)
 *           2 (     n     )
 */
static FLAC__fixedpoint local__compute_rbps_integerized(FLAC__uint32 err, FLAC__uint32 n)
{
	FLAC__uint32 rbps;
	unsigned bits; /* the number of bits required to represent a number */
	int fracbits; /* the number of bits of rbps that comprise the fractional part */

	FLAC__ASSERT(sizeof(rbps) == sizeof(FLAC__fixedpoint));
	FLAC__ASSERT(err > 0);
	FLAC__ASSERT(n > 0);

	FLAC__ASSERT(n <= FLAC__MAX_BLOCK_SIZE);
	if(err <= n)
		return 0;
	/*
	 * The above two things tell us 1) n fits in 16 bits; 2) err/n > 1.
	 * These allow us later to know we won't lose too much precision in the
	 * fixed-point division (err<<fracbits)/n.
	 */

	fracbits = (8*sizeof(err)) - (FLAC__bitmath_ilog2(err)+1);

	err <<= fracbits;
	err /= n;
	/* err now holds err/n with fracbits fractional bits */

	/*
	 * Whittle err down to 16 bits max.  16 significant bits is enough for
	 * our purposes.
	 */
	FLAC__ASSERT(err > 0);
	bits = FLAC__bitmath_ilog2(err)+1;
	if(bits > 16) {
		err >>= (bits-16);
		fracbits -= (bits-16);
	}
	rbps = (FLAC__uint32)err;

	/* Multiply by fixed-point version of ln(2), with 16 fractional bits */
	rbps *= FLAC__FP_LN2;
	fracbits += 16;
	FLAC__ASSERT(fracbits >= 0);

	/* FLAC__fixedpoint_log2 requires fracbits%4 to be 0 */
	{
		const int f = fracbits & 3;
		if(f) {
			rbps >>= f;
			fracbits -= f;
		}
	}

	rbps = FLAC__fixedpoint_log2(rbps, fracbits, (unsigned)(-1));

	if(rbps == 0)
		return 0;

	/*
	 * The return value must have 16 fractional bits.  Since the whole part
	 * of the base-2 log of a 32 bit number must fit in 5 bits, and fracbits
	 * must be >= -3, these assertion allows us to be able to shift rbps
	 * left if necessary to get 16 fracbits without losing any bits of the
	 * whole part of rbps.
	 *
	 * There is a slight chance due to accumulated error that the whole part
	 * will require 6 bits, so we use 6 in the assertion.  Really though as
	 * long as it fits in 13 bits (32 - (16 - (-3))) we are fine.
	 */
	FLAC__ASSERT((int)FLAC__bitmath_ilog2(rbps)+1 <= fracbits + 6);
	FLAC__ASSERT(fracbits >= -3);

	/* now shift the decimal point into place */
	if(fracbits < 16)
		return rbps << (16-fracbits);
	else if(fracbits > 16)
		return rbps >> (fracbits-16);
	else
		return rbps;
}

static FLAC__fixedpoint local__compute_rbps_wide_integerized(FLAC__uint64 err, FLAC__uint32 n)
{
	FLAC__uint32 rbps;
	unsigned bits; /* the number of bits required to represent a number */
	int fracbits; /* the number of bits of rbps that comprise the fractional part */

	FLAC__ASSERT(sizeof(rbps) == sizeof(FLAC__fixedpoint));
	FLAC__ASSERT(err > 0);
	FLAC__ASSERT(n > 0);

	FLAC__ASSERT(n <= FLAC__MAX_BLOCK_SIZE);
	if(err <= n)
		return 0;
	/*
	 * The above two things tell us 1) n fits in 16 bits; 2) err/n > 1.
	 * These allow us later to know we won't lose too much precision in the
	 * fixed-point division (err<<fracbits)/n.
	 */

	fracbits = (8*sizeof(err)) - (FLAC__bitmath_ilog2_wide(err)+1);

	err <<= fracbits;
	err /= n;
	/* err now holds err/n with fracbits fractional bits */

	/*
	 * Whittle err down to 16 bits max.  16 significant bits is enough for
	 * our purposes.
	 */
	FLAC__ASSERT(err > 0);
	bits = FLAC__bitmath_ilog2_wide(err)+1;
	if(bits > 16) {
		err >>= (bits-16);
		fracbits -= (bits-16);
	}
	rbps = (FLAC__uint32)err;

	/* Multiply by fixed-point version of ln(2), with 16 fractional bits */
	rbps *= FLAC__FP_LN2;
	fracbits += 16;
	FLAC__ASSERT(fracbits >= 0);

	/* FLAC__fixedpoint_log2 requires fracbits%4 to be 0 */
	{
		const int f = fracbits & 3;
		if(f) {
			rbps >>= f;
			fracbits -= f;
		}
	}

	rbps = FLAC__fixedpoint_log2(rbps, fracbits, (unsigned)(-1));

	if(rbps == 0)
		return 0;

	/*
	 * The return value must have 16 fractional bits.  Since the whole part
	 * of the base-2 log of a 32 bit number must fit in 5 bits, and fracbits
	 * must be >= -3, these assertion allows us to be able to shift rbps
	 * left if necessary to get 16 fracbits without losing any bits of the
	 * whole part of rbps.
	 *
	 * There is a slight chance due to accumulated error that the whole part
	 * will require 6 bits, so we use 6 in the assertion.  Really though as
	 * long as it fits in 13 bits (32 - (16 - (-3))) we are fine.
	 */
	FLAC__ASSERT((int)FLAC__bitmath_ilog2(rbps)+1 <= fracbits + 6);
	FLAC__ASSERT(fracbits >= -3);

	/* now shift the decimal point into place */
	if(fracbits < 16)
		return rbps << (16-fracbits);
	else if(fracbits > 16)
		return rbps >> (fracbits-16);