For the Roland LA32 PCM roms, the scrambling is consistent across the MT-32, D-50, CM-32L, LAPC-I, D-10/110, D-20/220, and is:

rawSample = BITSWAP16(rawSample, 15, 6, 14, 13, 12, 11, 10, 9, 8, 5, 4, 3, 2, 1, 0, 7);

This is using the BIT and BITSWAP macros from the older C versions of MAME (this specific code in question was always BSD licensed) and is reproduced below:

// from MAME, 3bsd

#define BIT(x,n) (((x)>>(n))&1)

#define BITSWAP8(val,B7,B6,B5,B4,B3,B2,B1,B0) \

((BIT(val,B7) << 7) | \

(BIT(val,B6) << 6) | \

(BIT(val,B5) << 5) | \

(BIT(val,B4) << 4) | \

(BIT(val,B3) << 3) | \

(BIT(val,B2) << 2) | \

(BIT(val,B1) << 1) | \

(BIT(val,B0) << 0))

#define BITSWAP16(val,B15,B14,B13,B12,B11,B10,B9,B8,B7,B6,B5,B4,B3,B2,B1,B0) \

((BIT(val,B15) << 15) | \

(BIT(val,B14) << 14) | \

(BIT(val,B13) << 13) | \

(BIT(val,B12) << 12) | \

(BIT(val,B11) << 11) | \

(BIT(val,B10) << 10) | \

(BIT(val, B9) << 9) | \

(BIT(val, B8) << 8) | \

(BIT(val, B7) << 7) | \

(BIT(val, B6) << 6) | \

(BIT(val, B5) << 5) | \

(BIT(val, B4) << 4) | \

(BIT(val, B3) << 3) | \

(BIT(val, B2) << 2) | \

(BIT(val, B1) << 1) | \

(BIT(val, B0) << 0))

Keep in mind the actual format the actual data is encoded in is a strange u-law like format which must be converted to PCM, there is a formula to do this as well. The LA32 internally uses a less accurate version of this using an exponential lookup table with linear interpolation between entries.

It can be done with pure integer math and that exponential lookup table, but the way I did it cheated and used floating point math:

for (int smpNum = 0; smpNum < len; smpNum += 2)

{

// parse out one sample

// first descramble the sample, which while stored in big endian,

// has the absolutely bizarre bit order of:

// 15, 6, 14, 13, 12, 11, 10, 9, 8, 5, 4, 3, 2, 1, 0, 7

int16_t rawSample = ( ((uint16_t)(*(ptr+smpNum)<<8)&0xFF00) |

((uint16_t)(*(ptr+smpNum+1)<<0)&0xFF) );

rawSample = BITSWAP16(rawSample, 15, 6, 14, 13, 12, 11, 10, 9, 8, 5, 4, 3, 2, 1, 0, 7);

double floatSample = pow(2.0f,(((rawSample & 0x7fff) - 32767.0f) / 2048.0f));

int16_t pcmSample = (floatSample * 32768.0f * ((rawSample&0x8000) ? -1.0f : 1.0f));

// little endian output because .wav

fputc((uint8_t)(pcmSample&0xFF), out);

fputc((uint8_t)(pcmSample>>8)&0xFF, out);

}

LN

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