adpcm.cc

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#include "swf.h"

#ifdef RCSID
static char *rcsid = "$Id: adpcm.cc,v 1.1.1.1 2002/01/25 22:14:58 kergoth Exp $";
#endif

// This file has been rearranged from the code posted
// on news:forums.macromedia.com by Jonathan Gay.
// Courtesy of Macromedia

//
// ADPCM tables
//

static const int indexTable2[2] = {
    -1, 2,
};

// Is this ok?
static const int indexTable3[4] = {
    -1, -1, 2, 4,
};

static const int indexTable4[8] = {
    -1, -1, -1, -1, 2, 4, 6, 8,
};

static const int indexTable5[16] = {
 -1, -1, -1, -1, -1, -1, -1, -1, 1, 2, 4, 6, 8, 10, 13, 16,
};

static const int* indexTables[] = {
 indexTable2,
 indexTable3,
 indexTable4,
 indexTable5
};

static const int 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
};

long
Adpcm::GetBits(int n)
{
        if ( bitPos < n ) FillBuffer();

        assert(bitPos >= n);

        long v = ((unsigned long)bitBuf << (32-bitPos)) >> (32-n);
        bitPos -= n;

        return v;
}

long
Adpcm::GetSBits(int n)
{
        if ( bitPos < n ) FillBuffer();

        assert(bitPos >= n);

        long v = ((long)bitBuf << (32-bitPos)) >> (32-n);
        bitPos -= n;

        return v;
}

//
// The Decompressor
//

// Constructor
Adpcm::Adpcm(unsigned char *buffer, long isStereo)
{
        stereo = isStereo;
        src = buffer;

        nBits = 0; // flag that it is not inited
        nSamples = 0;

        bitPos = 0;
        bitBuf = 0;
}

void
Adpcm::FillBuffer()
{
        while ( bitPos <= 24 /*&& srcSize > 0*/ ) {
                bitBuf = (bitBuf<<8) | *src++;
                bitPos += 8;
        }
}

void
Adpcm::Decompress(short *dst, long n)
{
        if ( nBits == 0 ) {
                // Get the compression header
                nBits = (int)GetBits(2)+2;
        }

        const int* indexTable = indexTables[nBits-2];
        int k0 = 1 << (nBits-2);
        int signmask = 1 << (nBits-1);

        if ( !stereo ) {
                // Optimize for mono
                long            vp = valpred[0]; // maybe these can get into registers...
                int             ind = index[0];
                long            ns = nSamples;

                while ( n-- > 0 ) {
                        ns++;

                        if ( (ns & 0xFFF) == 1 ) {
                                // Get a new block header
                                *dst++ = (short)(vp = GetSBits(16));

                                ind = (int)GetBits(6); // The first sample in a block does not have a delta
                        } else {
                                // Process a delta value
                                int delta = (int)GetBits(nBits);

                                // Compute difference and new predicted value
                                // Computes 'vpdiff = (delta+0.5)*step/4'
                                int step = stepsizeTable[ind];
                                long vpdiff = 0;
                                int k = k0;

                                do {
                                        if ( delta & k )
                                        vpdiff += step;
                                        step >>= 1;
                                        k >>= 1;
                                } while ( k );

                                vpdiff += step; // add 0.5

                                if ( delta & signmask ) // the sign bit
                                        vp -= vpdiff;
                                else
                                        vp += vpdiff;

                                // Find new index value
                                ind += indexTable[delta&(~signmask)];

                                if ( ind < 0 )
                                        ind = 0;
                                else if ( ind > 88 )
                                        ind = 88;

                                // clamp output value
                                if ( vp != (short)vp )
                                        vp = vp < 0 ? -32768 : 32767;

                                /* Step 7 - Output value */
                                *dst++ = (short)vp;
                        }
                }

                valpred[0] = vp;
                index[0] = ind;
                nSamples = ns;

        } else {
                int sn = stereo ? 2 : 1;

                // Stereo
                while ( n-- > 0 ) {

                        nSamples++;

                        if ( (nSamples & 0xFFF) == 1 ) {
                                // Get a new block header
                                for ( int i = 0; i < sn; i++ ) {

                                        *dst++ = (short)(valpred[i] = GetSBits(16));

                                        // The first sample in a block does not have a delta
                                        index[i] = (int)GetBits(6);
                                }
                        } else {
                                // Process a delta value
                                for ( int i = 0; i < sn; i++ ) {
                                        int delta = (int)GetBits(nBits);

                                        // Compute difference and new predicted value
                                        // Computes 'vpdiff = (delta+0.5)*step/4'

                                        int step = stepsizeTable[index[i]];
                                        long vpdiff = 0;
                                        int k = k0;

                                        do {
                                                if ( delta & k ) vpdiff += step;
                                                step >>= 1;
                                                k >>= 1;
                                        } while ( k );
                                        vpdiff += step; // add 0.5


                                        if ( delta & signmask ) // the sign bit
                                                valpred[i] -= vpdiff;
                                        else
                                                valpred[i] += vpdiff;

                                        // Find new index value
                                        index[i] += indexTable[delta&(~signmask)];

                                        if ( index[i] < 0 )
                                                index[i] = 0;
                                        else if ( index[i] > 88 )
                                                index[i] = 88;

                                        // clamp output value
                                        if ( valpred[i] != (short)valpred[i] )
                                                valpred[i] = valpred[i] < 0 ? -32768 : 32767;

                                        /* Step 7 - Output value */
                                        *dst++ = (short)valpred[i];
                                }
                        }
                }
        }
}

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