📄 adpcm_s.c
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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.
IntelDVI ADPCM coderdecoder.
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.
struct adpcm_state {
short valprev_l; Previous output value
char index_l; Index into stepsize table
short valprev_r; Previous output value
char index_r; Index into stepsize table
};
#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[];
int 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_l; Stepsize
long step_r; Stepsize
long valprev_l; virtual previous output value
long valprev_r; virtual previous output value
long vpdiff; Current change to valprev
long index_l; Current step change index
long index_r;
long outputbuffer; place to keep previous 4-bit value
outp = (signed char )outdata;
inp = indata;
valprev_l = state-valprev_l;
index_l = state-index_l;
step_l = stepsizeTable[index_l];
valprev_r = state-valprev_r;
index_r = state-index_r;
step_r = stepsizeTable[index_r];
for ( ; len 0 ; len-- )
{
LEFT CHANNEL
val = inp++;
Step 1 - compute difference with previous value
delta = val - valprev_l;
sign = (delta 0) 8 0;
if ( sign ) delta = (-delta);
Step 2 - Divide and clamp
#ifdef NODIVMUL
{
long tmp = 0;
vpdiff = 0;
if ( delta step_l ) {
tmp = 4;
delta -= step_l;
vpdiff = step_l;
}
step_l = 1;
if ( delta step_l ) {
tmp = 2;
delta -= step_l;
vpdiff += step_l;
}
step_l = 1;
if ( delta step_l ) {
tmp = 1;
vpdiff += step_l;
}
delta = tmp;
}
#else
delta = (delta2) step_l;
if ( delta 7 ) delta = 7;
vpdiff = (deltastep_l) 2;
#endif
Step 3 - Update previous value
if ( sign )
valprev_l -= vpdiff;
else
valprev_l += vpdiff;
Step 4 - Clamp previous value to 16 bits
if ( valprev_l 32767 )
valprev_l = 32767;
else if ( valprev_l -32768 )
valprev_l = -32768;
Step 5 - Assemble value, update index and step values
delta = sign;
index_l += indexTable[delta];
if ( index_l 0 ) index_l = 0;
if ( index_l 88 ) index_l = 88;
step_l = stepsizeTable[index_l];
Step 6 - Output value
outputbuffer = (delta 4) & 0xf0;
RIGHT CHANNEL
val = inp++;
Step 1 - compute difference with previous value
delta = val - valprev_r;
sign = (delta 0) 8 0;
if ( sign ) delta = (-delta);
Step 2 - Divide and clamp
#ifdef NODIVMUL
{
long tmp = 0;
vpdiff = 0;
if ( delta step_r ) {
tmp = 4;
delta -= step_r;
vpdiff = step_r;
}
step_r = 1;
if ( delta step_r ) {
tmp = 2;
delta -= step_r;
vpdiff += step_r;
}
step_r = 1;
if ( delta step_r ) {
tmp = 1;
vpdiff += step_r;
}
delta = tmp;
}
#else
delta = (delta2) step_r;
if ( delta 7 ) delta = 7;
vpdiff = (deltastep_r) 2;
#endif
Step 3 - Update previous value
if ( sign )
valprev_r -= vpdiff;
else
valprev_r += vpdiff;
Step 4 - Clamp previous value to 16 bits
if ( valprev_r 32767 )
valprev_r = 32767;
else if ( valprev_r -32768 )
valprev_r = -32768;
Step 5 - Assemble value, update index and step values
delta = sign;
index_r += indexTable[delta];
if ( index_r 0 ) index_r = 0;
if ( index_r 88 ) index_r = 88;
step_r = stepsizeTable[index_r];
Step 6 - Output value
outp++ = (delta & 0x0f) outputbuffer;
}
state-valprev_l = valprev_l;
state-index_l = index_l;
state-valprev_r = valprev_r;
state-index_r = index_r;
}
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_l; Stepsize
long step_r; Stepsize
long valprev_l; virtual previous output value
long valprev_r; virtual previous output value
long vpdiff; Current change to valprev
long index_l; Current step change index
long index_r; Current step change index
long inputbuffer; place to keep next 4-bit value
outp = outdata;
inp = (signed char )indata;
valprev_l = state-valprev_l;
index_l = state-index_l;
step_l = stepsizeTable[index_l];
valprev_r = state-valprev_r;
index_r = state-index_r;
step_r = stepsizeTable[index_r];
for ( ; len 0 ; len-- )
{
LEFT CHANNEL
Step 1 - get the delta value and compute next index
inputbuffer = inp++;
delta = (inputbuffer 4) & 0xf;
Step 2 - Find new index value (for later)
index_l += indexTable[delta];
if ( index_l 0 )
{
index_l = 0;
}
else if ( index_l 88 )
{
index_l = 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_l 2);
}
if ( delta & 2 )
{
vpdiff += (step_l 1);
}
if ( delta & 1 )
{
vpdiff += step_l;
}
vpdiff = 2;
#else
vpdiff = (deltastep_l) 2;
#endif
if ( sign )
valprev_l -= vpdiff;
else
valprev_l += vpdiff;
Step 5 - clamp output value
if ( valprev_l 32767 )
valprev_l = 32767;
else if ( valprev_l -32768 )
valprev_l = -32768;
Step 6 - Update step value
step_l = stepsizeTable[index_l];
Step 7 - Output value
outp++ = valprev_l;
RIGHT CHANNEL
Step 1 - get the delta value and compute next index
delta = inputbuffer & 0xf;
Step 2 - Find new index value (for later)
index_r += indexTable[delta];
if ( index_r 0 )
{
index_r = 0;
}
else if ( index_r 88 )
{
index_r = 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_r 2);
}
if ( delta & 2 )
{
vpdiff += (step_r 1);
}
if ( delta & 1 )
{
vpdiff += step_r;
}
vpdiff = 2;
#else
vpdiff = (deltastep_r) 2;
#endif
if ( sign )
valprev_r -= vpdiff;
else
valprev_r += vpdiff;
Step 5 - clamp output value
if ( valprev_r 32767 )
valprev_r = 32767;
else if ( valprev_r -32768 )
valprev_r = -32768;
Step 6 - Update step value
step_r = stepsizeTable[index_r];
Step 7 - Output value
outp++ = valprev_r;
}
state-valprev_l = valprev_l;
state-index_l = index_l;
state-valprev_r = valprev_r;
state-index_r = index_r;
}
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