313 lines
9.1 KiB
C
313 lines
9.1 KiB
C
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/*
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** Intel/DVI ADPCM coder/decoder.
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**
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** The algorithm for this coder was taken from the IMA Compatability Project
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** proceedings, Vol 2, Number 2; May 1992.
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**
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** Version 1.2, 18-Dec-92.
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**
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** Change log:
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** - Fixed a stupid bug, where the delta was computed as
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** stepsize*code/4 in stead of stepsize*(code+0.5)/4.
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** - There was an off-by-one error causing it to pick
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** an incorrect delta once in a blue moon.
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** - The NODIVMUL define has been removed. Computations are now always done
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** using shifts, adds and subtracts. It turned out that, because the standard
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** is defined using shift/add/subtract, you needed bits of fixup code
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** (because the div/mul simulation using shift/add/sub made some rounding
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** errors that real div/mul don't make) and all together the resultant code
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** ran slower than just using the shifts all the time.
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** - Changed some of the variable names to be more meaningful.
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*/
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#include "adpcm.h"
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#include "stdint.h"
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/* Intel ADPCM step variation table */
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const int8_t indexTable[16] = {
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-1, -1, -1, -1, 2, 4, 6, 8,
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-1, -1, -1, -1, 2, 4, 6, 8,
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};
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const uint16_t stepsizeTable[89] = {
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7, 8, 9, 10, 11, 12, 13, 14, 16, 17,
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19, 21, 23, 25, 28, 31, 34, 37, 41, 45,
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50, 55, 60, 66, 73, 80, 88, 97, 107, 118,
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130, 143, 157, 173, 190, 209, 230, 253, 279, 307,
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337, 371, 408, 449, 494, 544, 598, 658, 724, 796,
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876, 963, 1060, 1166, 1282, 1411, 1552, 1707, 1878, 2066,
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2272, 2499, 2749, 3024, 3327, 3660, 4026, 4428, 4871, 5358,
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5894, 6484, 7132, 7845, 8630, 9493, 10442, 11487, 12635, 13899,
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15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794, 32767
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};
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int adpcm_coder(short* indata, char* outdata, int len, struct adpcm_state* state)
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{
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int val; /* Current input sample value */
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unsigned int delta; /* Current adpcm output value */
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int diff; /* Difference between val and valprev */
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int step; /* Stepsize */
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int valpred; /* Predicted output value */
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int vpdiff; /* Current change to valpred */
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int index; /* Current step change index */
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unsigned int outputbuffer = 0;/* place to keep previous 4-bit value */
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int count = 0; /* the number of bytes encoded */
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valpred = state->valprev;
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index = (int)state->index;
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step = stepsizeTable[index];
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while (len > 0) {
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/* Step 1 - compute difference with previous value */
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val = *indata++;
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diff = val - valpred;
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if (diff < 0)
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{
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delta = 8;
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diff = (-diff);
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}
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else
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{
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delta = 0;
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}
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/* Step 2 - Divide and clamp */
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/* Note:
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** This code *approximately* computes:
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** delta = diff*4/step;
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** vpdiff = (delta+0.5)*step/4;
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** but in shift step bits are dropped. The net result of this is
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** that even if you have fast mul/div hardware you cannot put it to
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** good use since the fixup would be too expensive.
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*/
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vpdiff = (step >> 3);
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if (diff >= step) {
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delta |= 4;
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diff -= step;
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vpdiff += step;
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}
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step >>= 1;
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if (diff >= step) {
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delta |= 2;
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diff -= step;
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vpdiff += step;
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}
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step >>= 1;
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if (diff >= step) {
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delta |= 1;
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vpdiff += step;
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}
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/* Phil Frisbie combined steps 3 and 4 */
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/* Step 3 - Update previous value */
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/* Step 4 - Clamp previous value to 16 bits */
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if ((delta & 8) != 0)
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{
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valpred -= vpdiff;
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if (valpred < -32768)
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valpred = -32768;
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}
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else
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{
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valpred += vpdiff;
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if (valpred > 32767)
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valpred = 32767;
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}
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/* Step 5 - Assemble value, update index and step values */
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index += indexTable[delta];
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if (index < 0) index = 0;
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else if (index > 88) index = 88;
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step = stepsizeTable[index];
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/* Step 6 - Output value */
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outputbuffer = (delta << 4);
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/* Step 1 - compute difference with previous value */
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val = *indata++;
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diff = val - valpred;
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if (diff < 0)
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{
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delta = 8;
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diff = (-diff);
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}
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else
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{
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delta = 0;
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}
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/* Step 2 - Divide and clamp */
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/* Note:
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** This code *approximately* computes:
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** delta = diff*4/step;
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** vpdiff = (delta+0.5)*step/4;
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** but in shift step bits are dropped. The net result of this is
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** that even if you have fast mul/div hardware you cannot put it to
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** good use since the fixup would be too expensive.
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*/
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vpdiff = (step >> 3);
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if (diff >= step) {
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delta |= 4;
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diff -= step;
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vpdiff += step;
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}
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step >>= 1;
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if (diff >= step) {
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delta |= 2;
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diff -= step;
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vpdiff += step;
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}
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step >>= 1;
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if (diff >= step) {
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delta |= 1;
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vpdiff += step;
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}
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/* Phil Frisbie combined steps 3 and 4 */
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/* Step 3 - Update previous value */
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/* Step 4 - Clamp previous value to 16 bits */
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if ((delta & 8) != 0)
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{
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valpred -= vpdiff;
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if (valpred < -32768)
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valpred = -32768;
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}
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else
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{
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valpred += vpdiff;
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if (valpred > 32767)
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valpred = 32767;
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}
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/* Step 5 - Assemble value, update index and step values */
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index += indexTable[delta];
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if (index < 0) index = 0;
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else if (index > 88) index = 88;
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step = stepsizeTable[index];
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/* Step 6 - Output value */
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*outdata++ = (unsigned char)(delta | outputbuffer);
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count++;
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len -= 2;
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}
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state->valprev = (short)valpred;
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state->index = (char)index;
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return count;
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}
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// 解码
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int adpcm_decoder(char* indata, short* outdata, int len, struct adpcm_state* state)
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{
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unsigned int delta; /* Current adpcm output value */
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int step; /* Stepsize */
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int valpred; /* Predicted value */
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int vpdiff; /* Current change to valpred */
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int index; /* Current step change index */
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unsigned int inputbuffer = 0;/* place to keep next 4-bit value */
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int count = 0;
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valpred = state->valprev;
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index = (int)state->index;
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step = stepsizeTable[index];
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/* Loop unrolling by Phil Frisbie */
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/* This assumes there are ALWAYS an even number of samples */
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while (len-- > 0) {
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/* Step 1 - get the delta value */
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inputbuffer = (unsigned int)*indata++;
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delta = (inputbuffer >> 4) & 0xf;// &0xf 防止溢出
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/* Step 2 - Find new index value (for later) */
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index += indexTable[delta];
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if (index < 0) index = 0;
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else if (index > 88) index = 88;
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/* Phil Frisbie combined steps 3, 4, and 5 */
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/* Step 3 - Separate sign and magnitude */
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/* Step 4 - Compute difference and new predicted value */
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/* Step 5 - clamp output value */
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/*
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** Computes 'vpdiff = (delta+0.5)*step/4', but see comment
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** in adpcm_coder.
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*/
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vpdiff = step >> 3;
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if ((delta & 4) != 0) vpdiff += step;
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if ((delta & 2) != 0) vpdiff += step >> 1;
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if ((delta & 1) != 0) vpdiff += step >> 2;
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if ((delta & 8) != 0)
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{
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valpred -= vpdiff;
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if (valpred < -32768)
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valpred = -32768;
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}
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else
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{
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valpred += vpdiff;
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if (valpred > 32767)
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valpred = 32767;
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}
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/* Step 6 - Update step value */
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step = stepsizeTable[index];
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/* Step 7 - Output value */
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*outdata++ = (short)valpred;
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/* Step 1 - get the delta value */
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delta = inputbuffer & 0xf;
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/* Step 2 - Find new index value (for later) */
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index += indexTable[delta];
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if (index < 0) index = 0;
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else if (index > 88) index = 88;
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/* Phil Frisbie combined steps 3, 4, and 5 */
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/* Step 3 - Separate sign and magnitude */
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/* Step 4 - Compute difference and new predicted value */
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/* Step 5 - clamp output value */
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/*
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** Computes 'vpdiff = (delta+0.5)*step/4', but see comment
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** in adpcm_coder.
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*/
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vpdiff = step >> 3;
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if ((delta & 4) != 0) vpdiff += step;
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if ((delta & 2) != 0) vpdiff += step >> 1;
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if ((delta & 1) != 0) vpdiff += step >> 2;
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if ((delta & 8) != 0)
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{
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valpred -= vpdiff;
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if (valpred < -32768)
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valpred = -32768;
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}
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else
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{
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valpred += vpdiff;
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if (valpred > 32767)
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valpred = 32767;
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}
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/* Step 6 - Update step value */
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step = stepsizeTable[index];
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/* Step 7 - Output value */
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*outdata++ = (short)valpred;
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count += 2;
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}
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state->valprev = (short)valpred;
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state->index = (char)index;
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return count;
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}
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