g726.h

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00001 /*
00002  * SpanDSP - a series of DSP components for telephony
00003  *
00004  * g726.h - ITU G.726 codec.
00005  *
00006  * Written by Steve Underwood <steveu@coppice.org>
00007  *
00008  * Copyright (C) 2006 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 General Public License version 2, or
00014  * the Lesser GNU General Public License version 2.1, as published by
00015  * the Free Software Foundation.
00016  *
00017  * This program is distributed in the hope that it will be useful,
00018  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00019  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00020  * GNU General Public License for more details.
00021  *
00022  * You should have received a copy of the GNU General Public License
00023  * along with this program; if not, write to the Free Software
00024  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
00025  *
00026  * $Id: g726.h,v 1.19 2008/02/09 15:32:26 steveu Exp $
00027  */
00028 
00029 /*! \file */
00030 
00031 #if !defined(_SPANDSP_G726_H_)
00032 #define _SPANDSP_G726_H_
00033 
00034 /*! \page g726_page G.726 encoding and decoding
00035 \section g726_page_sec_1 What does it do?
00036 
00037 The G.726 module is a bit exact implementation of the full ITU G.726 specification.
00038 It supports:
00039     - 16 kbps, 24kbps, 32kbps, and 40kbps operation.
00040     - Tandem adjustment, for interworking with A-law and u-law.
00041     - Annex A support, for use in environments not using A-law or u-law.
00042 
00043 It passes the ITU tests.
00044 
00045 \section g726_page_sec_2 How does it work?
00046 ???.
00047 */
00048 
00049 enum
00050 {
00051     G726_ENCODING_LINEAR = 0,   /* Interworking with 16 bit signed linear */
00052     G726_ENCODING_ULAW,         /* Interworking with u-law */
00053     G726_ENCODING_ALAW          /* Interworking with A-law */
00054 };
00055 
00056 enum
00057 {
00058     G726_PACKING_NONE = 0,
00059     G726_PACKING_LEFT = 1,
00060     G726_PACKING_RIGHT = 2
00061 };
00062 
00063 struct g726_state_s;
00064 
00065 typedef int16_t (*g726_decoder_func_t)(struct g726_state_s *s, uint8_t code);
00066 
00067 typedef uint8_t (*g726_encoder_func_t)(struct g726_state_s *s, int16_t amp);
00068 
00069 /*!
00070  * The following is the definition of the state structure
00071  * used by the G.726 encoder and decoder to preserve their internal
00072  * state between successive calls.  The meanings of the majority
00073  * of the state structure fields are explained in detail in the
00074  * CCITT Recommendation G.721.  The field names are essentially indentical
00075  * to variable names in the bit level description of the coding algorithm
00076  * included in this Recommendation.
00077  */
00078 typedef struct g726_state_s
00079 {
00080     /*! The bit rate */
00081     int rate;
00082     /*! The external coding, for tandem operation */
00083     int ext_coding;
00084     /*! The number of bits per sample */
00085     unsigned int bits_per_sample;
00086     /*! One of the G.726_PACKING_xxx options */
00087     int packing;
00088 
00089     /*! Locked or steady state step size multiplier. */
00090     int32_t yl;
00091     /*! Unlocked or non-steady state step size multiplier. */
00092     int16_t yu;
00093     /*! int16_t term energy estimate. */
00094     int16_t dms;
00095     /*! Long term energy estimate. */
00096     int16_t dml;
00097     /*! Linear weighting coefficient of 'yl' and 'yu'. */
00098     int16_t ap;
00099     
00100     /*! Coefficients of pole portion of prediction filter. */
00101     int16_t a[2];
00102     /*! Coefficients of zero portion of prediction filter. */
00103     int16_t b[6];
00104     /*! Signs of previous two samples of a partially reconstructed signal. */
00105     int16_t pk[2];
00106     /*! Previous 6 samples of the quantized difference signal represented in
00107         an internal floating point format. */
00108     int16_t dq[6];
00109     /*! Previous 2 samples of the quantized difference signal represented in an
00110         internal floating point format. */
00111     int16_t sr[2];
00112     /*! Delayed tone detect */
00113     int td;
00114     
00115     /*! \brief The bit stream processing context. */
00116     bitstream_state_t bs;
00117 
00118     /*! \brief The current encoder function. */
00119     g726_encoder_func_t enc_func;
00120     /*! \brief The current decoder function. */
00121     g726_decoder_func_t dec_func;
00122 } g726_state_t;
00123 
00124 #if defined(__cplusplus)
00125 extern "C"
00126 {
00127 #endif
00128 
00129 /*! Initialise a G.726 encode or decode context.
00130     \param s The G.726 context.
00131     \param bit_rate The required bit rate for the ADPCM data.
00132            The valid rates are 16000, 24000, 32000 and 40000.
00133     \param ext_coding The coding used outside G.726.
00134     \param packing One of the G.726_PACKING_xxx options.
00135     \return A pointer to the G.726 context, or NULL for error. */
00136 g726_state_t *g726_init(g726_state_t *s, int bit_rate, int ext_coding, int packing);
00137 
00138 /*! Free a G.726 encode or decode context.
00139     \param s The G.726 context.
00140     \return 0 for OK. */
00141 int g726_release(g726_state_t *s);
00142 
00143 /*! Decode a buffer of G.726 ADPCM data to linear PCM, a-law or u-law.
00144     \param s The G.726 context.
00145     \param amp The audio sample buffer.
00146     \param g726_data
00147     \param g726_bytes
00148     \return The number of samples returned. */
00149 int g726_decode(g726_state_t *s,
00150                 int16_t amp[],
00151                 const uint8_t g726_data[],
00152                 int g726_bytes);
00153 
00154 /*! Encode a buffer of linear PCM data to G.726 ADPCM.
00155     \param s The G.726 context.
00156     \param g726_data The G.726 data produced.
00157     \param amp The audio sample buffer.
00158     \param len The number of samples in the buffer.
00159     \return The number of bytes of G.726 data produced. */
00160 int g726_encode(g726_state_t *s,
00161                 uint8_t g726_data[],
00162                 const int16_t amp[],
00163                 int len);
00164 
00165 #if defined(__cplusplus)
00166 }
00167 #endif
00168 
00169 #endif
00170 /*- End of file ------------------------------------------------------------*/

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