adpcm.c

G.726 ADPCM算法在C语言上的实现代码

/***********************************************************  
Copyright 1992 by Stichting Mathematisch Centrum, Amsterdam, The  
Netherlands.  
  
                        All Rights Reserved  
  
Permission to use, copy, modify, and distribute this software and its  
documentation for any purpose and without fee is hereby granted,  
provided that the above copyright notice appear in all copies and that  
both that copyright notice and this permission notice appear in  
supporting documentation, and that the names of Stichting Mathematisch  
Centrum or CWI not be used in advertising or publicity pertaining to  
distribution of the software without specific, written prior permission.  
  
STICHTING MATHEMATISCH CENTRUM DISCLAIMS ALL WARRANTIES WITH REGARD TO  
THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND  
FITNESS, IN NO EVENT SHALL STICHTING MATHEMATISCH CENTRUM BE LIABLE  
FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES  
WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN  
ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT  
OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.  
  
******************************************************************/   
   
/*  
** Intel/DVI ADPCM coder/decoder.  
**  
** The algorithm for this coder was taken from the IMA Compatability Project  
** proceedings, Vol 2, Number 2; May 1992.  
**  
** Version 1.0, 7-Jul-92.  
*/   
   
#include "adpcm.h"    
   
#ifndef __STDC__    
#define signed    
#endif    
   
#define NODIVMUL    
   
/* Intel ADPCM step variation table */   
static long indexTable[16] = {   
    -1, -1, -1, -1, 2, 4, 6, 8,   
    -1, -1, -1, -1, 2, 4, 6, 8,   
};   
   
static long stepsizeTable[89] = {   
    7, 8, 9, 10, 11, 12, 13, 14, 16, 17,   
    19, 21, 23, 25, 28, 31, 34, 37, 41, 45,   
    50, 55, 60, 66, 73, 80, 88, 97, 107, 118,   
    130, 143, 157, 173, 190, 209, 230, 253, 279, 307,   
    337, 371, 408, 449, 494, 544, 598, 658, 724, 796,   
    876, 963, 1060, 1166, 1282, 1411, 1552, 1707, 1878, 2066,   
    2272, 2499, 2749, 3024, 3327, 3660, 4026, 4428, 4871, 5358,   
    5894, 6484, 7132, 7845, 8630, 9493, 10442, 11487, 12635, 13899,   
    15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794, 32767   
};   
   
void   
adpcm_coder(indata, outdata, len, state)   
    short indata[];   
    char outdata[];   
    long len;   
    struct adpcm_state *state;   
{   
    short *inp;                        /* Input buffer pointer */   
    signed char *outp;         /* output buffer pointer */   
    long val;                   /* Current input sample value */   
    long sign;                  /* Current adpcm sign bit */   
    long delta;                 /* Current adpcm output value */   
    long step;                  /* Stepsize */   
    long valprev;               /* virtual previous output value */   
    long vpdiff;                        /* Current change to valprev */   
    long index;                 /* Current step change index */   
    long outputbuffer;          /* place to keep previous 4-bit value */   
    long bufferstep;            /* toggle between outputbuffer/output */   
   
    outp = (signed char *)outdata;   
    inp = indata;   
   
    valprev = state->valprev;   
    index = state->index;   
    step = stepsizeTable[index];   
   
    bufferstep = 1;   
   
    for ( ; len > 0 ; len-- ) {   
       val = *inp++;   
   
       /* Step 1 - compute difference with previous value */   
       delta = val - valprev;   
       sign = (delta < 0) ? 8 : 0;   
       if ( sign ) delta = (-delta);   
   
       /* Step 2 - Divide and clamp */   
#ifdef NODIVMUL    
        {   
           long tmp = 0;   
   
           vpdiff = 0;   
           if ( delta > step ) {   
               tmp = 4;   
               delta -= step;   
               vpdiff = step;   
           }   
           step >>= 1;   
           if ( delta > step  ) {   
               tmp |= 2;   
               delta -= step;   
               vpdiff += step;   
           }   
           step >>= 1;   
           if ( delta > step ) {   
               tmp |= 1;   
               vpdiff += step;   
           }   
           delta = tmp;   
       }   
#else    
       delta = (delta<<2) / step;   
       if ( delta > 7 ) delta = 7;   
   
       vpdiff = (delta*step) >> 2;   
#endif    
   
       /* Step 3 - Update previous value */   
       if ( sign )   
         valprev -= vpdiff;   
       else   
         valprev += vpdiff;   
   
       /* Step 4 - Clamp previous value to 16 bits */   
       if ( valprev > 32767 )   
         valprev = 32767;   
       else if ( valprev < -32768 )   
         valprev = -32768;   
   
       /* Step 5 - Assemble value, update index and step values */   
       delta |= sign;   
   
       index += indexTable[delta];   
       if ( index < 0 ) index = 0;   
       if ( index > 88 ) index = 88;   
       step = stepsizeTable[index];   
   
       /* Step 6 - Output value */   
       if ( bufferstep ) {   
           outputbuffer = (delta << 4) & 0xf0;   
       } else {   
           *outp++ = (delta & 0x0f) | outputbuffer;   
       }   
       bufferstep = !bufferstep;   
    }   
   
    /* Output last step, if needed */   
    if ( !bufferstep )   
      *outp++ = outputbuffer;   
   
    state->valprev = valprev;   
    state->index = index;   
}   
   
void   
adpcm_decoder(indata, outdata, len, state)   
    char indata[];   
    short outdata[];   
    int len;   
    struct adpcm_state *state;   
{   
    signed char *inp;          /* Input buffer pointer */   
    short *outp;               /* output buffer pointer */   
    long sign;                  /* Current adpcm sign bit */   
    long delta;                 /* Current adpcm output value */   
    long step;                  /* Stepsize */   
    long valprev;               /* virtual previous output value */   
    long vpdiff;                        /* Current change to valprev */   
    long index;                 /* Current step change index */   
    long inputbuffer;           /* place to keep next 4-bit value */   
    long bufferstep;            /* toggle between inputbuffer/input */   
   
    outp = outdata;   
    inp = (signed char *)indata;   
   
    valprev = state->valprev;   
    index = state->index;   
    step = stepsizeTable[index];   
   
    bufferstep = 0;   
   
    len *=2;   
   
    for ( ; len > 0 ; len-- ) {   
   
       /* Step 1 - get the delta value and compute next index */   
       if ( bufferstep ) {   
           delta = inputbuffer & 0xf;   
       } else {   
           inputbuffer = *inp++;   
           delta = (inputbuffer >> 4) & 0xf;   
       }   
       bufferstep = !bufferstep;   
   
        /* Step 2 - Find new index value (for later) */   
        index += indexTable[delta];   
        if ( index < 0 )   
        {   
            index = 0;   
        }   
        else if ( index > 88 )   
        {   
            index = 88;   
        }   
   
       /* Step 3 - Separate sign and magnitude */   
       sign = delta & 8;   
       delta = delta & 7;   
   
       /* Step 4 - update output value */   
#ifdef NODIVMUL    
        vpdiff = 0;   
        if ( delta & 4 )   
        {   
            vpdiff  = (step << 2);   
        }   
        if ( delta & 2 )   
        {   
            vpdiff += (step << 1);   
        }   
        if ( delta & 1 )   
        {   
            vpdiff += step;   
        }   
        vpdiff >>= 2;   
#else    
        vpdiff = (delta*step) >> 2;   
#endif    
       if ( sign )   
         valprev -= vpdiff;   
       else   
         valprev += vpdiff;   
   
       /* Step 5 - clamp output value */   
       if ( valprev > 32767 )   
         valprev = 32767;   
       else if ( valprev < -32768 )   
         valprev = -32768;   
   
       /* Step 6 - Update step value */   
       step = stepsizeTable[index];   
   
       /* Step 7 - Output value */   
       *outp++ = valprev;   
    }   
   
    state->valprev = valprev;   
    state->index = index;   
}