PS1 SPU-ADPCM decoder

// PS1 SPU-ADPCM decoder
// A lot of nooooise :'( probably the algorithm is wrong
// https://dl.dropboxusercontent.com/u/26695489/adpcm/AUDIO.ADPCM

#include <stdio.h>
#include <stdint.h>
#include <assert.h>

typedef struct {
    int32_t s_1;
    int32_t s_2;
} AdpcmState;

const int32_t FILTER0[5] = { 0, 60, 115, 98, 122 };
const int32_t FILTER1[5] = { 0, 0, -52, -55, -60 };
const float CurrentVolume = 0.0002f;

int32_t Clamp(int32_t n, int32_t min, int32_t max)
{
    if (n < min) return min;
    if (n > max) return max;
    return n;
}
int32_t Volume(int32_t n, float volume)
{
    return (int32_t)((float)n * volume);
}

void Decode(int16_t *pOut, uint8_t *pIn, AdpcmState *state)
{
    int shift = (*pIn & 0x0F);
    int filter = (*pIn >> 4) & 0x0F;
    int flags = pIn[1];

    int32_t f0 = FILTER0[filter];
    int32_t f1 = FILTER1[filter];
    for (int i = 2, nSample = 0; i < 16; i++)
    {
        int data = pIn[i];
        int nl = (signed)((data << 28) & 0xF0000000) >> shift;
        int nh = (signed)((data << 24) & 0xF0000000) >> shift;
        nl += ((f0 * state->s_1) + (f1 * state->s_2) + 32) >> 6;
        nh += ((f0 * nl) + (f1 * state->s_1) + 32) >> 6;
        state->s_2 = nl;
        state->s_1 = nh;
        pOut[nSample++] = Clamp(Volume(nl, CurrentVolume), -32768, +32767);
        pOut[nSample++] = Clamp(Volume(nh, CurrentVolume), -32768, +32767);
    }
}

int main()
{
    uint8_t buf[16];
    int16_t pcm[28];
    AdpcmState state;
    FILE *fIn = fopen("AUDIO.ADPCM", "rb");
    FILE *fOut = fopen("AUDIO.PCM", "wb");
    assert(fIn != NULL);
    assert(fOut != NULL);
    state.s_1 = state.s_2 = 0;
    while (fread(buf, sizeof(buf), 1, fIn) == 1)
    {
        Decode(pcm, buf, &state);
        fwrite(pcm, sizeof(pcm), 1, fOut);
    }
    fclose(fOut);
    fclose(fIn);
}