IMA_ADPCM.cpp

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/*
This program is distributed under the terms of the 'MIT license'. The text
of this licence follows...

Copyright (c) 2005 J.D.Medhurst (a.k.a. Tixy)

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/

#include "common.h"
#include "IMA_ADPCM.h"


static const uint16_t IMA_ADPCMStepTable[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
    };


static const int IMA_ADPCMIndexTable[8] =
    {
    -1, -1, -1, -1, 2, 4, 6, 8,
    };


EXPORT void IMA_ADPCM::EncodeInit(int16_t sample1,int16_t sample2)
    {
    PredictedValue = sample1;
    int delta = sample2-sample1;
    if(delta<0)
        delta = - delta;
    if(delta>32767)
        delta = 32767;
    int stepIndex = 0;
    while(IMA_ADPCMStepTable[stepIndex]<(unsigned)delta)
        stepIndex++;
    StepIndex = stepIndex;
    }


EXPORT unsigned IMA_ADPCM::Encode(int16_t pcm16)
    {
    int predicedValue = PredictedValue;
    int stepIndex = StepIndex;

    int delta = pcm16-predicedValue;
    unsigned value;
    if(delta>=0)
        value = 0;
    else
        {
        value = 8;
        delta = -delta;
        }

    int step = IMA_ADPCMStepTable[stepIndex];
    int diff = step>>3;
    if(delta>step)
        {
        value |= 4;
        delta -= step;
        diff += step;
        }
    step >>= 1;
    if(delta>step)
        {
        value |= 2;
        delta -= step;
        diff += step;
        }
    step >>= 1;
    if(delta>step)
        {
        value |= 1;
        diff += step;
        }

    if(value&8)
        predicedValue -= diff;
    else
        predicedValue += diff;
    if(predicedValue<-0x8000)
        predicedValue = -0x8000;
    else if(predicedValue>0x7fff)
        predicedValue = 0x7fff;
    PredictedValue = predicedValue;

    stepIndex += IMA_ADPCMIndexTable[value&7];
    if(stepIndex<0)
        stepIndex = 0;
    else if(stepIndex>88)
        stepIndex = 88;
    StepIndex = stepIndex;

    return value;
    }


EXPORT int IMA_ADPCM::Decode(unsigned adpcm)
    {
    int stepIndex = StepIndex;
    int step = IMA_ADPCMStepTable[stepIndex];

    stepIndex += IMA_ADPCMIndexTable[adpcm&7];
    if(stepIndex<0)
        stepIndex = 0;
    else if(stepIndex>88)
        stepIndex = 88;
    StepIndex = stepIndex;

    int diff = step>>3;
    if(adpcm&4)
        diff += step;
    if(adpcm&2)
        diff += step>>1;
    if(adpcm&1)
        diff += step>>2;

    int predicedValue = PredictedValue;
    if(adpcm&8)
        predicedValue -= diff;
    else
        predicedValue += diff;
    if(predicedValue<-0x8000)
        predicedValue = -0x8000;
    else if(predicedValue>0x7fff)
        predicedValue = 0x7fff;
    PredictedValue = predicedValue;

    return predicedValue;
    }


EXPORT unsigned IMA_ADPCM::Encode(uint8_t* dst, int dstOffset, const int16_t* src, size_t srcSize)
    {
    // use given bit offset
    dst += dstOffset>>3;
    unsigned bitOffset = dstOffset&4;

    // make sure srcSize represents a whole number of samples
    srcSize &= ~1;

    // calculate end of input buffer
    const int16_t* end = (const int16_t*)((const uint8_t*)src+srcSize);

    while(src<end)
        {
        // encode a pcm value from input buffer
        unsigned adpcm = Encode(*src++);

        // pick which nibble to write adpcm value to...
        if(!bitOffset)
            *dst = adpcm;       // write adpcm value to low nibble
        else
            {
            unsigned b = *dst;      // get byte from ouput
            b &= 0x0f;          // clear bits of high nibble
            b |= adpcm<<4;      // or adpcm value into the high nibble
            *dst++ = (uint8_t)b;    // write value back to output and move on to next byte
            }

        // toggle which nibble in byte to write to next
        bitOffset ^= 4;         
        }

    // return number bits written to dst
    return srcSize*2;
    }


EXPORT unsigned IMA_ADPCM::Decode(int16_t* dst, const uint8_t* src, int srcOffset, unsigned srcSize)
    {
    // use given bit offset
    src += srcOffset>>3;

    // calculate pointers to iterate output buffer
    int16_t* out = dst;
    int16_t* end = out+(srcSize>>2);

    while(out<end)
        {
        // get byte from src
        unsigned adpcm = *src; 

        // pick which nibble holds a adpcm value...
        if(srcOffset&4)
            {
            adpcm >>= 4;  // use high nibble of byte
            ++src;        // move on a byte for next sample
            }

        *out++ = Decode(adpcm);  // decode value and store it

        // toggle which nibble in byte to write to next
        srcOffset ^= 4;
        }

    // return number of bytes written to dst
    return (unsigned)out-(unsigned)dst;
    }

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