00001 /* 00002 * SpanDSP - a series of DSP components for telephony 00003 * 00004 * g711.h - In line A-law and u-law conversion routines 00005 * 00006 * Written by Steve Underwood <steveu@coppice.org> 00007 * 00008 * Copyright (C) 2001 Steve Underwood 00009 * 00010 * All rights reserved. 00011 * 00012 * This program is free software; you can redistribute it and/or modify 00013 * it under the terms of the GNU Lesser General Public License version 2.1, 00014 * as published by the Free Software Foundation. 00015 * 00016 * This program is distributed in the hope that it will be useful, 00017 * but WITHOUT ANY WARRANTY; without even the implied warranty of 00018 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 00019 * GNU Lesser General Public License for more details. 00020 * 00021 * You should have received a copy of the GNU Lesser General Public 00022 * License along with this program; if not, write to the Free Software 00023 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. 00024 * 00025 * $Id: g711.h,v 1.19 2009/04/12 09:12:10 steveu Exp $ 00026 */ 00027 00028 /*! \file */ 00029 00030 /*! \page g711_page A-law and mu-law handling 00031 Lookup tables for A-law and u-law look attractive, until you consider the impact 00032 on the CPU cache. If it causes a substantial area of your processor cache to get 00033 hit too often, cache sloshing will severely slow things down. The main reason 00034 these routines are slow in C, is the lack of direct access to the CPU's "find 00035 the first 1" instruction. A little in-line assembler fixes that, and the 00036 conversion routines can be faster than lookup tables, in most real world usage. 00037 A "find the first 1" instruction is available on most modern CPUs, and is a 00038 much underused feature. 00039 00040 If an assembly language method of bit searching is not available, these routines 00041 revert to a method that can be a little slow, so the cache thrashing might not 00042 seem so bad :( 00043 00044 Feel free to submit patches to add fast "find the first 1" support for your own 00045 favourite processor. 00046 00047 Look up tables are used for transcoding between A-law and u-law, since it is 00048 difficult to achieve the precise transcoding procedure laid down in the G.711 00049 specification by other means. 00050 */ 00051 00052 #if !defined(_SPANDSP_G711_H_) 00053 #define _SPANDSP_G711_H_ 00054 00055 /* The usual values to use on idle channels, to emulate silence */ 00056 /*! Idle value for A-law channels */ 00057 #define G711_ALAW_IDLE_OCTET 0x5D 00058 /*! Idle value for u-law channels */ 00059 #define G711_ULAW_IDLE_OCTET 0xFF 00060 00061 enum 00062 { 00063 G711_ALAW = 0, 00064 G711_ULAW 00065 }; 00066 00067 /*! 00068 G.711 state 00069 */ 00070 typedef struct g711_state_s g711_state_t; 00071 00072 #if defined(__cplusplus) 00073 extern "C" 00074 { 00075 #endif 00076 00077 /* N.B. It is tempting to use look-up tables for A-law and u-law conversion. 00078 * However, you should consider the cache footprint. 00079 * 00080 * A 64K byte table for linear to x-law and a 512 byte table for x-law to 00081 * linear sound like peanuts these days, and shouldn't an array lookup be 00082 * real fast? No! When the cache sloshes as badly as this one will, a tight 00083 * calculation may be better. The messiest part is normally finding the 00084 * segment, but a little inline assembly can fix that on an i386, x86_64 and 00085 * many other modern processors. 00086 */ 00087 00088 /* 00089 * Mu-law is basically as follows: 00090 * 00091 * Biased Linear Input Code Compressed Code 00092 * ------------------------ --------------- 00093 * 00000001wxyza 000wxyz 00094 * 0000001wxyzab 001wxyz 00095 * 000001wxyzabc 010wxyz 00096 * 00001wxyzabcd 011wxyz 00097 * 0001wxyzabcde 100wxyz 00098 * 001wxyzabcdef 101wxyz 00099 * 01wxyzabcdefg 110wxyz 00100 * 1wxyzabcdefgh 111wxyz 00101 * 00102 * Each biased linear code has a leading 1 which identifies the segment 00103 * number. The value of the segment number is equal to 7 minus the number 00104 * of leading 0's. The quantization interval is directly available as the 00105 * four bits wxyz. * The trailing bits (a - h) are ignored. 00106 * 00107 * Ordinarily the complement of the resulting code word is used for 00108 * transmission, and so the code word is complemented before it is returned. 00109 * 00110 * For further information see John C. Bellamy's Digital Telephony, 1982, 00111 * John Wiley & Sons, pps 98-111 and 472-476. 00112 */ 00113 00114 /* Enable the trap as per the MIL-STD */ 00115 //#define ULAW_ZEROTRAP 00116 /*! Bias for u-law encoding from linear. */ 00117 #define ULAW_BIAS 0x84 00118 00119 /*! \brief Encode a linear sample to u-law 00120 \param linear The sample to encode. 00121 \return The u-law value. 00122 */ 00123 static __inline__ uint8_t linear_to_ulaw(int linear) 00124 { 00125 uint8_t u_val; 00126 int mask; 00127 int seg; 00128 00129 /* Get the sign and the magnitude of the value. */ 00130 if (linear >= 0) 00131 { 00132 linear = ULAW_BIAS + linear; 00133 mask = 0xFF; 00134 } 00135 else 00136 { 00137 linear = ULAW_BIAS - linear; 00138 mask = 0x7F; 00139 } 00140 00141 seg = top_bit(linear | 0xFF) - 7; 00142 00143 /* 00144 * Combine the sign, segment, quantization bits, 00145 * and complement the code word. 00146 */ 00147 if (seg >= 8) 00148 u_val = (uint8_t) (0x7F ^ mask); 00149 else 00150 u_val = (uint8_t) (((seg << 4) | ((linear >> (seg + 3)) & 0xF)) ^ mask); 00151 #ifdef ULAW_ZEROTRAP 00152 /* Optional ITU trap */ 00153 if (u_val == 0) 00154 u_val = 0x02; 00155 #endif 00156 return u_val; 00157 } 00158 /*- End of function --------------------------------------------------------*/ 00159 00160 /*! \brief Decode an u-law sample to a linear value. 00161 \param ulaw The u-law sample to decode. 00162 \return The linear value. 00163 */ 00164 static __inline__ int16_t ulaw_to_linear(uint8_t ulaw) 00165 { 00166 int t; 00167 00168 /* Complement to obtain normal u-law value. */ 00169 ulaw = ~ulaw; 00170 /* 00171 * Extract and bias the quantization bits. Then 00172 * shift up by the segment number and subtract out the bias. 00173 */ 00174 t = (((ulaw & 0x0F) << 3) + ULAW_BIAS) << (((int) ulaw & 0x70) >> 4); 00175 return (int16_t) ((ulaw & 0x80) ? (ULAW_BIAS - t) : (t - ULAW_BIAS)); 00176 } 00177 /*- End of function --------------------------------------------------------*/ 00178 00179 /* 00180 * A-law is basically as follows: 00181 * 00182 * Linear Input Code Compressed Code 00183 * ----------------- --------------- 00184 * 0000000wxyza 000wxyz 00185 * 0000001wxyza 001wxyz 00186 * 000001wxyzab 010wxyz 00187 * 00001wxyzabc 011wxyz 00188 * 0001wxyzabcd 100wxyz 00189 * 001wxyzabcde 101wxyz 00190 * 01wxyzabcdef 110wxyz 00191 * 1wxyzabcdefg 111wxyz 00192 * 00193 * For further information see John C. Bellamy's Digital Telephony, 1982, 00194 * John Wiley & Sons, pps 98-111 and 472-476. 00195 */ 00196 00197 /*! The A-law alternate mark inversion mask */ 00198 #define ALAW_AMI_MASK 0x55 00199 00200 /*! \brief Encode a linear sample to A-law 00201 \param linear The sample to encode. 00202 \return The A-law value. 00203 */ 00204 static __inline__ uint8_t linear_to_alaw(int linear) 00205 { 00206 int mask; 00207 int seg; 00208 00209 if (linear >= 0) 00210 { 00211 /* Sign (bit 7) bit = 1 */ 00212 mask = ALAW_AMI_MASK | 0x80; 00213 } 00214 else 00215 { 00216 /* Sign (bit 7) bit = 0 */ 00217 mask = ALAW_AMI_MASK; 00218 linear = -linear - 1; 00219 } 00220 00221 /* Convert the scaled magnitude to segment number. */ 00222 seg = top_bit(linear | 0xFF) - 7; 00223 if (seg >= 8) 00224 { 00225 if (linear >= 0) 00226 { 00227 /* Out of range. Return maximum value. */ 00228 return (uint8_t) (0x7F ^ mask); 00229 } 00230 /* We must be just a tiny step below zero */ 00231 return (uint8_t) (0x00 ^ mask); 00232 } 00233 /* Combine the sign, segment, and quantization bits. */ 00234 return (uint8_t) (((seg << 4) | ((linear >> ((seg) ? (seg + 3) : 4)) & 0x0F)) ^ mask); 00235 } 00236 /*- End of function --------------------------------------------------------*/ 00237 00238 /*! \brief Decode an A-law sample to a linear value. 00239 \param alaw The A-law sample to decode. 00240 \return The linear value. 00241 */ 00242 static __inline__ int16_t alaw_to_linear(uint8_t alaw) 00243 { 00244 int i; 00245 int seg; 00246 00247 alaw ^= ALAW_AMI_MASK; 00248 i = ((alaw & 0x0F) << 4); 00249 seg = (((int) alaw & 0x70) >> 4); 00250 if (seg) 00251 i = (i + 0x108) << (seg - 1); 00252 else 00253 i += 8; 00254 return (int16_t) ((alaw & 0x80) ? i : -i); 00255 } 00256 /*- End of function --------------------------------------------------------*/ 00257 00258 /*! \brief Transcode from A-law to u-law, using the procedure defined in G.711. 00259 \param alaw The A-law sample to transcode. 00260 \return The best matching u-law value. 00261 */ 00262 SPAN_DECLARE(uint8_t) alaw_to_ulaw(uint8_t alaw); 00263 00264 /*! \brief Transcode from u-law to A-law, using the procedure defined in G.711. 00265 \param ulaw The u-law sample to transcode. 00266 \return The best matching A-law value. 00267 */ 00268 SPAN_DECLARE(uint8_t) ulaw_to_alaw(uint8_t ulaw); 00269 00270 /*! \brief Decode from u-law or A-law to linear. 00271 \param s The G.711 context. 00272 \param amp The linear audio buffer. 00273 \param g711_data The G.711 data. 00274 \param g711_bytes The number of G.711 samples to decode. 00275 \return The number of samples of linear audio produced. 00276 */ 00277 SPAN_DECLARE(int) g711_decode(g711_state_t *s, 00278 int16_t amp[], 00279 const uint8_t g711_data[], 00280 int g711_bytes); 00281 00282 /*! \brief Encode from linear to u-law or A-law. 00283 \param s The G.711 context. 00284 \param g711_data The G.711 data. 00285 \param amp The linear audio buffer. 00286 \param len The number of samples to encode. 00287 \return The number of G.711 samples produced. 00288 */ 00289 SPAN_DECLARE(int) g711_encode(g711_state_t *s, 00290 uint8_t g711_data[], 00291 const int16_t amp[], 00292 int len); 00293 00294 /*! \brief Transcode between u-law and A-law. 00295 \param s The G.711 context. 00296 \param g711_out The resulting G.711 data. 00297 \param g711_in The original G.711 data. 00298 \param g711_bytes The number of G.711 samples to transcode. 00299 \return The number of G.711 samples produced. 00300 */ 00301 SPAN_DECLARE(int) g711_transcode(g711_state_t *s, 00302 uint8_t g711_out[], 00303 const uint8_t g711_in[], 00304 int g711_bytes); 00305 00306 /*! Initialise a G.711 encode or decode context. 00307 \param s The G.711 context. 00308 \param mode The G.711 mode. 00309 \return A pointer to the G.711 context, or NULL for error. */ 00310 SPAN_DECLARE(g711_state_t *) g711_init(g711_state_t *s, int mode); 00311 00312 /*! Release a G.711 encode or decode context. 00313 \param s The G.711 context. 00314 \return 0 for OK. */ 00315 SPAN_DECLARE(int) g711_release(g711_state_t *s); 00316 00317 /*! Free a G.711 encode or decode context. 00318 \param s The G.711 context. 00319 \return 0 for OK. */ 00320 SPAN_DECLARE(int) g711_free(g711_state_t *s); 00321 00322 #if defined(__cplusplus) 00323 } 00324 #endif 00325 00326 #endif 00327 /*- End of file ------------------------------------------------------------*/