/* * SpanDSP - a series of DSP components for telephony * * g711.h - In line A-law and u-law conversion routines * * Written by Steve Underwood <[email protected]> * * Copyright (C) 2001 Steve Underwood * * Despite my general liking of the GPL, I place this code in the * public domain for the benefit of all mankind - even the slimy * ones who might try to proprietize my work and use it to my * detriment. * * $Id: g711.h,v 1.1 2006/06/07 15:46:39 steveu Exp $ * * Modifications for WebRtc, 2011/04/28, by tlegrand: * -Changed to use WebRtc types * -Changed __inline__ to __inline * -Two changes to make implementation bitexact with ITU-T reference * implementation */ /*! \page g711_page A-law and mu-law handling Lookup tables for A-law and u-law look attractive, until you consider the impact on the CPU cache. If it causes a substantial area of your processor cache to get hit too often, cache sloshing will severely slow things down. The main reason these routines are slow in C, is the lack of direct access to the CPU's "find the first 1" instruction. A little in-line assembler fixes that, and the conversion routines can be faster than lookup tables, in most real world usage. A "find the first 1" instruction is available on most modern CPUs, and is a much underused feature. If an assembly language method of bit searching is not available, these routines revert to a method that can be a little slow, so the cache thrashing might not seem so bad :( Feel free to submit patches to add fast "find the first 1" support for your own favourite processor. Look up tables are used for transcoding between A-law and u-law, since it is difficult to achieve the precise transcoding procedure laid down in the G.711 specification by other means. */ #ifndef MODULES_THIRD_PARTY_G711_G711_H_ #define MODULES_THIRD_PARTY_G711_G711_H_ #ifdef __cplusplus extern "C" { #endif #include <stdint.h> #if defined(__i386__) /*! \brief Find the bit position of the highest set bit in a word \param bits The word to be searched \return The bit number of the highest set bit, or -1 if the word is zero. */ static __inline__ int top_bit(unsigned int bits) { int res; __asm__ __volatile__( " movl $-1,%%edx;\n" " bsrl %%eax,%%edx;\n" : "=d"(res) : "a"(bits)); return res; } /*! \brief Find the bit position of the lowest set bit in a word \param bits The word to be searched \return The bit number of the lowest set bit, or -1 if the word is zero. */ static __inline__ int bottom_bit(unsigned int bits) { int res; __asm__ __volatile__( " movl $-1,%%edx;\n" " bsfl %%eax,%%edx;\n" : "=d"(res) : "a"(bits)); return res; } #elif defined(__x86_64__) static __inline__ int top_bit(unsigned int bits) { … } static __inline__ int bottom_bit(unsigned int bits) { … } #else static __inline int top_bit(unsigned int bits) { int i; if (bits == 0) { return -1; } i = 0; if (bits & 0xFFFF0000) { bits &= 0xFFFF0000; i += 16; } if (bits & 0xFF00FF00) { bits &= 0xFF00FF00; i += 8; } if (bits & 0xF0F0F0F0) { bits &= 0xF0F0F0F0; i += 4; } if (bits & 0xCCCCCCCC) { bits &= 0xCCCCCCCC; i += 2; } if (bits & 0xAAAAAAAA) { bits &= 0xAAAAAAAA; i += 1; } return i; } static __inline int bottom_bit(unsigned int bits) { int i; if (bits == 0) { return -1; } i = 32; if (bits & 0x0000FFFF) { bits &= 0x0000FFFF; i -= 16; } if (bits & 0x00FF00FF) { bits &= 0x00FF00FF; i -= 8; } if (bits & 0x0F0F0F0F) { bits &= 0x0F0F0F0F; i -= 4; } if (bits & 0x33333333) { bits &= 0x33333333; i -= 2; } if (bits & 0x55555555) { bits &= 0x55555555; i -= 1; } return i; } #endif /* N.B. It is tempting to use look-up tables for A-law and u-law conversion. * However, you should consider the cache footprint. * * A 64K byte table for linear to x-law and a 512 byte table for x-law to * linear sound like peanuts these days, and shouldn't an array lookup be * real fast? No! When the cache sloshes as badly as this one will, a tight * calculation may be better. The messiest part is normally finding the * segment, but a little inline assembly can fix that on an i386, x86_64 * and many other modern processors. */ /* * Mu-law is basically as follows: * * Biased Linear Input Code Compressed Code * ------------------------ --------------- * 00000001wxyza 000wxyz * 0000001wxyzab 001wxyz * 000001wxyzabc 010wxyz * 00001wxyzabcd 011wxyz * 0001wxyzabcde 100wxyz * 001wxyzabcdef 101wxyz * 01wxyzabcdefg 110wxyz * 1wxyzabcdefgh 111wxyz * * Each biased linear code has a leading 1 which identifies the segment * number. The value of the segment number is equal to 7 minus the number * of leading 0's. The quantization interval is directly available as the * four bits wxyz. * The trailing bits (a - h) are ignored. * * Ordinarily the complement of the resulting code word is used for * transmission, and so the code word is complemented before it is returned. * * For further information see John C. Bellamy's Digital Telephony, 1982, * John Wiley & Sons, pps 98-111 and 472-476. */ // #define ULAW_ZEROTRAP /* turn on the trap as per the MIL-STD //*/ #define ULAW_BIAS … /*! \brief Encode a linear sample to u-law \param linear The sample to encode. \return The u-law value. */ static __inline uint8_t linear_to_ulaw(int linear) { … } /*! \brief Decode an u-law sample to a linear value. \param ulaw The u-law sample to decode. \return The linear value. */ static __inline int16_t ulaw_to_linear(uint8_t ulaw) { … } /* * A-law is basically as follows: * * Linear Input Code Compressed Code * ----------------- --------------- * 0000000wxyza 000wxyz * 0000001wxyza 001wxyz * 000001wxyzab 010wxyz * 00001wxyzabc 011wxyz * 0001wxyzabcd 100wxyz * 001wxyzabcde 101wxyz * 01wxyzabcdef 110wxyz * 1wxyzabcdefg 111wxyz * * For further information see John C. Bellamy's Digital Telephony, 1982, * John Wiley & Sons, pps 98-111 and 472-476. */ #define ALAW_AMI_MASK … /*! \brief Encode a linear sample to A-law \param linear The sample to encode. \return The A-law value. */ static __inline uint8_t linear_to_alaw(int linear) { … } /*! \brief Decode an A-law sample to a linear value. \param alaw The A-law sample to decode. \return The linear value. */ static __inline int16_t alaw_to_linear(uint8_t alaw) { … } /*! \brief Transcode from A-law to u-law, using the procedure defined in G.711. \param alaw The A-law sample to transcode. \return The best matching u-law value. */ uint8_t alaw_to_ulaw(uint8_t alaw); /*! \brief Transcode from u-law to A-law, using the procedure defined in G.711. \param alaw The u-law sample to transcode. \return The best matching A-law value. */ uint8_t ulaw_to_alaw(uint8_t ulaw); #ifdef __cplusplus } #endif #endif /* MODULES_THIRD_PARTY_G711_G711_H_ */
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