/*
** 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 1.2, 18-Dec-92.
**
** Change log:
** - Fixed a stupid bug, where the delta was computed as
**   stepsize*code/4 in stead of stepsize*(code+0.5)/4.
** - There was an off-by-one error causing it to pick
**   an incorrect delta once in a blue moon.
** - The NODIVMUL define has been removed. Computations are now always done
**   using shifts, adds and subtracts. It turned out that, because the standard
**   is defined using shift/add/subtract, you needed bits of fixup code
**   (because the div/mul simulation using shift/add/sub made some rounding
**   errors that real div/mul don't make) and all together the resultant code
**   ran slower than just using the shifts all the time.
** - Changed some of the variable names to be more meaningful.
*/
 
#include "adpcm.h"
#include "stdint.h"

/* Intel ADPCM step variation table */
const int8_t indexTable[16] = {
    -1, -1, -1, -1, 2, 4, 6, 8,
    -1, -1, -1, -1, 2, 4, 6, 8,
};
 
const uint16_t 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
};
 
 
int adpcm_coder(short* indata, char* outdata, int len, struct adpcm_state* state)
{
    int val;   /* Current input sample value */
    unsigned int delta; /* Current adpcm output value */
    int diff;   /* Difference between val and valprev */
    int step;         /* Stepsize */
    int valpred;  /* Predicted output value */
    int vpdiff;         /* Current change to valpred */
    int index;   /* Current step change index */
    unsigned int outputbuffer = 0;/* place to keep previous 4-bit value */
    int count = 0;      /* the number of bytes encoded */
 
    valpred = state->valprev;
    index = (int)state->index;
    step = stepsizeTable[index];
 
    while (len > 0) {
        /* Step 1 - compute difference with previous value */
        val = *indata++;
        diff = val - valpred;
        if (diff < 0)
        {
            delta = 8;
            diff = (-diff);
        }
        else
        {
            delta = 0;
        }
 
        /* Step 2 - Divide and clamp */
        /* Note:
        ** This code *approximately* computes:
        **    delta = diff*4/step;
        **    vpdiff = (delta+0.5)*step/4;
        ** but in shift step bits are dropped. The net result of this is
        ** that even if you have fast mul/div hardware you cannot put it to
        ** good use since the fixup would be too expensive.
        */
        vpdiff = (step >> 3);
 
        if (diff >= step) {
            delta |= 4;
            diff -= step;
            vpdiff += step;
        }
        step >>= 1;
        if (diff >= step) {
            delta |= 2;
            diff -= step;
            vpdiff += step;
        }
        step >>= 1;
        if (diff >= step) {
            delta |= 1;
            vpdiff += step;
        }
 
        /* Phil Frisbie combined steps 3 and 4 */
        /* Step 3 - Update previous value */
        /* Step 4 - Clamp previous value to 16 bits */
        if ((delta & 8) != 0)
        {
            valpred -= vpdiff;
            if (valpred < -32768)
                valpred = -32768;
        }
        else
        {
            valpred += vpdiff;
            if (valpred > 32767)
                valpred = 32767;
        }
 
        /* Step 5 - Assemble value, update index and step values */
        index += indexTable[delta];
        if (index < 0) index = 0;
        else if (index > 88) index = 88;
        step = stepsizeTable[index];
 
        /* Step 6 - Output value */
        outputbuffer = (delta << 4);
 
        /* Step 1 - compute difference with previous value */
        val = *indata++;
        diff = val - valpred;
        if (diff < 0)
        {
            delta = 8;
            diff = (-diff);
        }
        else
        {
            delta = 0;
        }
 
        /* Step 2 - Divide and clamp */
        /* Note:
        ** This code *approximately* computes:
        **    delta = diff*4/step;
        **    vpdiff = (delta+0.5)*step/4;
        ** but in shift step bits are dropped. The net result of this is
        ** that even if you have fast mul/div hardware you cannot put it to
        ** good use since the fixup would be too expensive.
        */
        vpdiff = (step >> 3);
 
        if (diff >= step) {
            delta |= 4;
            diff -= step;
            vpdiff += step;
        }
        step >>= 1;
        if (diff >= step) {
            delta |= 2;
            diff -= step;
            vpdiff += step;
        }
        step >>= 1;
        if (diff >= step) {
            delta |= 1;
            vpdiff += step;
        }
 
        /* Phil Frisbie combined steps 3 and 4 */
        /* Step 3 - Update previous value */
        /* Step 4 - Clamp previous value to 16 bits */
        if ((delta & 8) != 0)
        {
            valpred -= vpdiff;
            if (valpred < -32768)
                valpred = -32768;
        }
        else
        {
            valpred += vpdiff;
            if (valpred > 32767)
                valpred = 32767;
        }
 
        /* Step 5 - Assemble value, update index and step values */
        index += indexTable[delta];
        if (index < 0) index = 0;
        else if (index > 88) index = 88;
        step = stepsizeTable[index];
 
        /* Step 6 - Output value */
        *outdata++ = (unsigned char)(delta | outputbuffer);
        count++;
        len -= 2;
    }
 
    state->valprev = (short)valpred;
    state->index = (char)index;
 
    return count;
}
 
// 解码
int adpcm_decoder(char* indata, short* outdata, int len, struct adpcm_state* state)
{
    unsigned int delta; /* Current adpcm output value */
    int step;         /* Stepsize */
    int valpred;  /* Predicted value */
    int vpdiff;         /* Current change to valpred */
    int index;   /* Current step change index */
    unsigned int inputbuffer = 0;/* place to keep next 4-bit value */
    int count = 0;
 
    valpred = state->valprev;
    index = (int)state->index;
    step = stepsizeTable[index];
 
    /* Loop unrolling by Phil Frisbie */
    /* This assumes there are ALWAYS an even number of samples */
    while (len-- > 0) {
 
        /* Step 1 - get the delta value */
        inputbuffer = (unsigned int)*indata++;
        delta = (inputbuffer >> 4) & 0xf;// &0xf 防止溢出
      
        /* Step 2 - Find new index value (for later) */
  
        index += indexTable[delta];
        if (index < 0) index = 0;
        else if (index > 88) index = 88;
     
 
 
        /* Phil Frisbie combined steps 3, 4, and 5 */
        /* Step 3 - Separate sign and magnitude */
        /* Step 4 - Compute difference and new predicted value */
        /* Step 5 - clamp output value */
        /*
        ** Computes 'vpdiff = (delta+0.5)*step/4', but see comment
        ** in adpcm_coder.
        */
        vpdiff = step >> 3;
        if ((delta & 4) != 0) vpdiff += step;
        if ((delta & 2) != 0) vpdiff += step >> 1;
        if ((delta & 1) != 0) vpdiff += step >> 2;
 
        if ((delta & 8) != 0)
        {
            valpred -= vpdiff;
            if (valpred < -32768)
                valpred = -32768;
        }
        else
        {
            valpred += vpdiff;
            if (valpred > 32767)
                valpred = 32767;
        }
 
        /* Step 6 - Update step value */
        step = stepsizeTable[index];
 
        /* Step 7 - Output value */
        *outdata++ = (short)valpred;
 
        /* Step 1 - get the delta value */
        delta = inputbuffer & 0xf;
 
        /* Step 2 - Find new index value (for later) */
        index += indexTable[delta];
        if (index < 0) index = 0;
        else if (index > 88) index = 88;
 
        /* Phil Frisbie combined steps 3, 4, and 5 */
        /* Step 3 - Separate sign and magnitude */
        /* Step 4 - Compute difference and new predicted value */
        /* Step 5 - clamp output value */
        /*
        ** Computes 'vpdiff = (delta+0.5)*step/4', but see comment
        ** in adpcm_coder.
        */
        vpdiff = step >> 3;
        if ((delta & 4) != 0) vpdiff += step;
        if ((delta & 2) != 0) vpdiff += step >> 1;
        if ((delta & 1) != 0) vpdiff += step >> 2;
 
        if ((delta & 8) != 0)
        {
            valpred -= vpdiff;
            if (valpred < -32768)
                valpred = -32768;
        }
        else
        {
            valpred += vpdiff;
            if (valpred > 32767)
                valpred = 32767;
        }
 
        /* Step 6 - Update step value */
        step = stepsizeTable[index];
 
        /* Step 7 - Output value */
        *outdata++ = (short)valpred;
        count += 2;
    }
 
    state->valprev = (short)valpred;
    state->index = (char)index;
 
    return count;
}