#include <stdio.h>
//
#include "proto.h"
#include "adpcm.h"


static S32 indexTable2[2] = { -1, 2 };
static S32 indexTable3[4] = { -1, -1, 2, 4 };
static S32 indexTable4[8] = { -1, -1, -1, -1, 2, 4, 6, 8 };
static S32 indexTable5[16] = { -1, -1, -1, -1, -1, -1, -1, -1, 1, 2, 4, 6, 8, 10, 13, 16 };
static S32* indexTables[] = { indexTable2, indexTable3, indexTable4, indexTable5 };

static S32 stepsizeTable[89] = {
  7, 8, 9, 10, 11, 12, 13, 14, 16, 17,
  19, 21, 23, 25, 28, 31, 34, 37, 41, 45,
  50, 55, 60, 66, 73, 80, 88, 97, 107, 118,
  130, 143, 157, 173, 190, 209, 230, 253, 279, 307,
  337, 371, 408, 449, 494, 544, 598, 658, 724, 796,
  876, 963, 1060, 1166, 1282, 1411, 1552, 1707, 1878, 2066,
  2272, 2499, 2749, 3024, 3327, 3660, 4026, 4428, 4871, 5358,
  5894, 6484, 7132, 7845, 8630, 9493, 10442, 11487, 12635, 13899,
  15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794, 32767
};



void adpcm_init(ADPCMSTATE *state) {
  state->index = 0;
  state->prev = 0;
}


S32 adpcm_compress(S16 sample, ADPCMSTATE *state, S32 bits) {

  S32 delta, compressed, prev, index, vpdiff, stepsize, i;
  S32 *indextable;

  indextable = indexTables[bits-2];
  bits--;

  prev = state->prev;
  index = state->index;
  stepsize = stepsizeTable[index];

  delta = sample-prev;

  if (delta < 0) {
    compressed = 1<<bits;
    delta = -delta;
  } else
    compressed = 0;

  // sort of divide...
  vpdiff = stepsize>>bits;
  for (i = bits-1; i >= 0; i--) {
    if (delta > stepsize) {
      compressed |= 1<<i;
      delta -= stepsize;
      vpdiff += stepsize;
    }
    stepsize >>= 1;
  }

  // update and clamp prev
  if (compressed & (1<<bits))
    prev -= vpdiff;
  else
    prev += vpdiff;
  if (prev > 32767)   prev = 32767;
  if (prev < -32767)  prev = -32767;
  state->prev = prev;

  // update and clamp index
  index += indextable[compressed &((1<<bits)-1)];
  if (index < 0)   index = 0;
  if (index > 88)  index = 88;
  state->index = index;

  return compressed;
}
