vgmstream/src/coding/ngc_dsp_decoder.c

#include "ngc_dsp_decoder.h"
#include "../util.h"

void decode_ngc_dsp(VGMSTREAMCHANNEL * stream, sample * outbuf, int channelspacing, int32_t first_sample, int32_t samples_to_do) {
    int i=first_sample;
    int32_t sample_count;

    int framesin = first_sample/14;

    int8_t header = read_8bit(framesin*8+stream->offset,stream->streamfile);
    int32_t scale = 1 << (header & 0xf);
    int coef_index = (header >> 4) & 0xf;
    int32_t hist1 = stream->adpcm_history1_16;
    int32_t hist2 = stream->adpcm_history2_16;
    int coef1 = stream->adpcm_coef[coef_index*2];
    int coef2 = stream->adpcm_coef[coef_index*2+1];

    first_sample = first_sample%14;

    for (i=first_sample,sample_count=0; i<first_sample+samples_to_do; i++,sample_count+=channelspacing) {
        int sample_byte = read_8bit(framesin*8+stream->offset+1+i/2,stream->streamfile);

        outbuf[sample_count] = clamp16((
                 (((i&1?
                    get_low_nibble_signed(sample_byte):
                    get_high_nibble_signed(sample_byte)
                   ) * scale)<<11) + 1024 +
                 (coef1 * hist1 + coef2 * hist2))>>11
                );

        hist2 = hist1;
        hist1 = outbuf[sample_count];
    }

    stream->adpcm_history1_16 = hist1;
    stream->adpcm_history2_16 = hist2;
}

/*
 * The original DSP spec uses nibble counts for loop points, and some
 * variants don't have a proper sample count, so all we (who are interested
 * in sample counts) need to do this conversion occasionally.
 */
int32_t dsp_nibbles_to_samples(int32_t nibbles) {
    int32_t whole_frames = nibbles/16;
    int32_t remainder = nibbles%16;

    if (remainder > 0 && remainder < 14)
        return whole_frames*14 + remainder;
    else if (remainder >= 14)
        fprintf(stderr,"last frame %d leftover nibbles makes no sense\n",remainder);
    return whole_frames*14;
}