/* 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[], dest[];
LONG n;
BYTE x;
   {
   BYTE d;
   LONG 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[], dest[];
LONG n;
   {
   D1Unpack(source+2, n-2, dest, source[1]);
   }