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345 lines
9.6 KiB
C
345 lines
9.6 KiB
C
/*
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* SpanDSP - a series of DSP components for telephony
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*
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* g711.h - In line A-law and u-law conversion routines
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*
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* Written by Steve Underwood <steveu@coppice.org>
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*
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* Copyright (C) 2001 Steve Underwood
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*
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* Despite my general liking of the GPL, I place this code in the
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* public domain for the benefit of all mankind - even the slimy
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* ones who might try to proprietize my work and use it to my
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* detriment.
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*
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* $Id: g711.h,v 1.1 2006/06/07 15:46:39 steveu Exp $
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*
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* Modifications for WebRtc, 2011/04/28, by tlegrand:
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* -Changed to use WebRtc types
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* -Changed __inline__ to __inline
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* -Two changes to make implementation bitexact with ITU-T reference implementation
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*/
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/*! \page g711_page A-law and mu-law handling
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Lookup tables for A-law and u-law look attractive, until you consider the impact
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on the CPU cache. If it causes a substantial area of your processor cache to get
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hit too often, cache sloshing will severely slow things down. The main reason
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these routines are slow in C, is the lack of direct access to the CPU's "find
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the first 1" instruction. A little in-line assembler fixes that, and the
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conversion routines can be faster than lookup tables, in most real world usage.
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A "find the first 1" instruction is available on most modern CPUs, and is a
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much underused feature.
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If an assembly language method of bit searching is not available, these routines
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revert to a method that can be a little slow, so the cache thrashing might not
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seem so bad :(
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Feel free to submit patches to add fast "find the first 1" support for your own
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favourite processor.
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Look up tables are used for transcoding between A-law and u-law, since it is
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difficult to achieve the precise transcoding procedure laid down in the G.711
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specification by other means.
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*/
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#if !defined(_G711_H_)
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#define _G711_H_
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#ifdef __cplusplus
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extern "C" {
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#endif
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#include "typedefs.h"
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#if defined(__i386__)
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/*! \brief Find the bit position of the highest set bit in a word
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\param bits The word to be searched
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\return The bit number of the highest set bit, or -1 if the word is zero. */
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static __inline__ int top_bit(unsigned int bits) {
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int res;
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__asm__ __volatile__(" movl $-1,%%edx;\n"
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" bsrl %%eax,%%edx;\n"
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: "=d" (res)
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: "a" (bits));
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return res;
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}
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/*! \brief Find the bit position of the lowest set bit in a word
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\param bits The word to be searched
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\return The bit number of the lowest set bit, or -1 if the word is zero. */
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static __inline__ int bottom_bit(unsigned int bits) {
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int res;
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__asm__ __volatile__(" movl $-1,%%edx;\n"
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" bsfl %%eax,%%edx;\n"
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: "=d" (res)
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: "a" (bits));
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return res;
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}
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#elif defined(__x86_64__)
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static __inline__ int top_bit(unsigned int bits) {
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int res;
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__asm__ __volatile__(" movq $-1,%%rdx;\n"
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" bsrq %%rax,%%rdx;\n"
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: "=d" (res)
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: "a" (bits));
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return res;
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}
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static __inline__ int bottom_bit(unsigned int bits) {
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int res;
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__asm__ __volatile__(" movq $-1,%%rdx;\n"
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" bsfq %%rax,%%rdx;\n"
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: "=d" (res)
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: "a" (bits));
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return res;
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}
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#else
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static __inline int top_bit(unsigned int bits) {
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int i;
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if (bits == 0) {
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return -1;
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}
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i = 0;
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if (bits & 0xFFFF0000) {
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bits &= 0xFFFF0000;
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i += 16;
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}
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if (bits & 0xFF00FF00) {
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bits &= 0xFF00FF00;
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i += 8;
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}
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if (bits & 0xF0F0F0F0) {
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bits &= 0xF0F0F0F0;
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i += 4;
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}
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if (bits & 0xCCCCCCCC) {
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bits &= 0xCCCCCCCC;
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i += 2;
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}
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if (bits & 0xAAAAAAAA) {
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bits &= 0xAAAAAAAA;
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i += 1;
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}
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return i;
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}
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static __inline int bottom_bit(unsigned int bits) {
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int i;
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if (bits == 0) {
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return -1;
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}
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i = 32;
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if (bits & 0x0000FFFF) {
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bits &= 0x0000FFFF;
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i -= 16;
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}
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if (bits & 0x00FF00FF) {
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bits &= 0x00FF00FF;
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i -= 8;
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}
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if (bits & 0x0F0F0F0F) {
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bits &= 0x0F0F0F0F;
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i -= 4;
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}
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if (bits & 0x33333333) {
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bits &= 0x33333333;
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i -= 2;
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}
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if (bits & 0x55555555) {
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bits &= 0x55555555;
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i -= 1;
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}
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return i;
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}
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#endif
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/* N.B. It is tempting to use look-up tables for A-law and u-law conversion.
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* However, you should consider the cache footprint.
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*
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* A 64K byte table for linear to x-law and a 512 byte table for x-law to
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* linear sound like peanuts these days, and shouldn't an array lookup be
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* real fast? No! When the cache sloshes as badly as this one will, a tight
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* calculation may be better. The messiest part is normally finding the
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* segment, but a little inline assembly can fix that on an i386, x86_64 and
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* many other modern processors.
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*/
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/*
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* Mu-law is basically as follows:
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*
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* Biased Linear Input Code Compressed Code
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* ------------------------ ---------------
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* 00000001wxyza 000wxyz
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* 0000001wxyzab 001wxyz
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* 000001wxyzabc 010wxyz
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* 00001wxyzabcd 011wxyz
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* 0001wxyzabcde 100wxyz
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* 001wxyzabcdef 101wxyz
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* 01wxyzabcdefg 110wxyz
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* 1wxyzabcdefgh 111wxyz
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*
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* Each biased linear code has a leading 1 which identifies the segment
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* number. The value of the segment number is equal to 7 minus the number
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* of leading 0's. The quantization interval is directly available as the
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* four bits wxyz. * The trailing bits (a - h) are ignored.
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*
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* Ordinarily the complement of the resulting code word is used for
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* transmission, and so the code word is complemented before it is returned.
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*
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* For further information see John C. Bellamy's Digital Telephony, 1982,
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* John Wiley & Sons, pps 98-111 and 472-476.
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*/
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//#define ULAW_ZEROTRAP /* turn on the trap as per the MIL-STD */
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#define ULAW_BIAS 0x84 /* Bias for linear code. */
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/*! \brief Encode a linear sample to u-law
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\param linear The sample to encode.
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\return The u-law value.
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*/
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static __inline uint8_t linear_to_ulaw(int linear) {
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uint8_t u_val;
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int mask;
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int seg;
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/* Get the sign and the magnitude of the value. */
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if (linear < 0) {
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/* WebRtc, tlegrand: -1 added to get bitexact to reference implementation */
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linear = ULAW_BIAS - linear - 1;
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mask = 0x7F;
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} else {
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linear = ULAW_BIAS + linear;
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mask = 0xFF;
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}
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seg = top_bit(linear | 0xFF) - 7;
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/*
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* Combine the sign, segment, quantization bits,
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* and complement the code word.
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*/
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if (seg >= 8)
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u_val = (uint8_t)(0x7F ^ mask);
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else
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u_val = (uint8_t)(((seg << 4) | ((linear >> (seg + 3)) & 0xF)) ^ mask);
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#ifdef ULAW_ZEROTRAP
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/* Optional ITU trap */
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if (u_val == 0)
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u_val = 0x02;
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#endif
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return u_val;
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}
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/*! \brief Decode an u-law sample to a linear value.
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\param ulaw The u-law sample to decode.
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\return The linear value.
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*/
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static __inline int16_t ulaw_to_linear(uint8_t ulaw) {
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int t;
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/* Complement to obtain normal u-law value. */
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ulaw = ~ulaw;
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/*
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* Extract and bias the quantization bits. Then
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* shift up by the segment number and subtract out the bias.
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*/
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t = (((ulaw & 0x0F) << 3) + ULAW_BIAS) << (((int) ulaw & 0x70) >> 4);
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return (int16_t)((ulaw & 0x80) ? (ULAW_BIAS - t) : (t - ULAW_BIAS));
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}
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/*
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* A-law is basically as follows:
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*
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* Linear Input Code Compressed Code
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* ----------------- ---------------
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* 0000000wxyza 000wxyz
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* 0000001wxyza 001wxyz
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* 000001wxyzab 010wxyz
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* 00001wxyzabc 011wxyz
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* 0001wxyzabcd 100wxyz
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* 001wxyzabcde 101wxyz
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* 01wxyzabcdef 110wxyz
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* 1wxyzabcdefg 111wxyz
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*
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* For further information see John C. Bellamy's Digital Telephony, 1982,
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* John Wiley & Sons, pps 98-111 and 472-476.
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*/
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#define ALAW_AMI_MASK 0x55
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/*! \brief Encode a linear sample to A-law
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\param linear The sample to encode.
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\return The A-law value.
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*/
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static __inline uint8_t linear_to_alaw(int linear) {
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int mask;
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int seg;
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if (linear >= 0) {
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/* Sign (bit 7) bit = 1 */
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mask = ALAW_AMI_MASK | 0x80;
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} else {
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/* Sign (bit 7) bit = 0 */
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mask = ALAW_AMI_MASK;
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/* WebRtc, tlegrand: Changed from -8 to -1 to get bitexact to reference
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* implementation */
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linear = -linear - 1;
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}
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/* Convert the scaled magnitude to segment number. */
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seg = top_bit(linear | 0xFF) - 7;
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if (seg >= 8) {
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if (linear >= 0) {
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/* Out of range. Return maximum value. */
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return (uint8_t)(0x7F ^ mask);
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}
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/* We must be just a tiny step below zero */
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return (uint8_t)(0x00 ^ mask);
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}
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/* Combine the sign, segment, and quantization bits. */
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return (uint8_t)(((seg << 4) | ((linear >> ((seg) ? (seg + 3) : 4)) & 0x0F)) ^
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mask);
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}
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/*! \brief Decode an A-law sample to a linear value.
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\param alaw The A-law sample to decode.
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\return The linear value.
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*/
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static __inline int16_t alaw_to_linear(uint8_t alaw) {
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int i;
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int seg;
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alaw ^= ALAW_AMI_MASK;
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i = ((alaw & 0x0F) << 4);
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seg = (((int) alaw & 0x70) >> 4);
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if (seg)
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i = (i + 0x108) << (seg - 1);
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else
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i += 8;
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return (int16_t)((alaw & 0x80) ? i : -i);
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}
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/*! \brief Transcode from A-law to u-law, using the procedure defined in G.711.
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\param alaw The A-law sample to transcode.
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\return The best matching u-law value.
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*/
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uint8_t alaw_to_ulaw(uint8_t alaw);
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/*! \brief Transcode from u-law to A-law, using the procedure defined in G.711.
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\param alaw The u-law sample to transcode.
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\return The best matching A-law value.
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*/
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uint8_t ulaw_to_alaw(uint8_t ulaw);
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#ifdef __cplusplus
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}
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#endif
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#endif
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