/* DUnpack.c --- Fibonacci Delta decompression by Steve Hayes */

#include <exec/types.h>

/* Fibonacci delta encoding for sound data */
BYTE codeToDelta[16] = {-34,-21,-13,-8,-5,-3,-2,-1,0,1,2,3,5,8,13,21};

/* Unpack Fibonacci-delta encoded data from n byte source
 * buffer into 2*n byte dest buffer, given initial data
 * value x.  It returns the lats data value x so you can
 * call it several times to incrementally decompress the data.
 */

BYTE D1Unpack(source,n,dest,x)
	BYTE	*source;
	ULONG	n;
	BYTE	*dest;
	BYTE	x;
{
	UBYTE	d;
	ULONG	i, lim;

	lim = n << 1;
	for (i=0; i < lim; ++i) {
		/* Decode a data nibble, high nibble then low nibble */
		d = source[i >> 1];	/* get a pair of nibbles */
		if (i & 1) {		/* select low or high nibble */
			d &= 0xf;	/* mask to get the low nibble */
		} else {
			d >>= 4;	/* shift to get the high nibble */
		}
		x += codeToDelta[d];	/* add in the decoded delta */
		dest[i] = x;		/* store a 1 byte sample */
	}
	return(x);
}

/* Unpack Fibonacci-delta encoded data from n byte
 * source buffer into 2*(n-2) byte dest buffer.
 * Source buffer has a pad byte, an 8-bit initial
 * value, followed by n-2 bytes comprising 2*(n-2)
 * 4-bit encoded samples.
 */

void DUnpack(source, n, dest)
	BYTE	*source;
	ULONG	n;
	BYTE	*dest;
{
	D1Unpack(source+2, n-2, dest, source[1]);
}