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// license:BSD-3-Clause
// copyright-holders:Andrew Gardner,Aaron Giles
/***************************************************************************
imaadpcm.cpp
IMA ADPCM emulation.
***************************************************************************/
#include "emu.h"
#include "imaadpcm.h"
//**************************************************************************
// ADPCM STATE HELPER
//**************************************************************************
// ADPCM state and tables
bool ima_adpcm_state::s_tables_computed = false;
const int8_t ima_adpcm_state::s_index_shift[8] = { -1, -1, -1, -1, 2, 4, 6, 8 };
int ima_adpcm_state::s_diff_lookup[89*16];
//-------------------------------------------------
// reset - reset the ADPCM state
//-------------------------------------------------
void ima_adpcm_state::reset()
{
// reset the signal/step
m_signal = m_loop_signal = 0;
m_step = m_loop_step = 0;
m_saved = false;
}
//-------------------------------------------------
// clock - decode single nibble and update
// ADPCM output
//-------------------------------------------------
int16_t ima_adpcm_state::clock(uint8_t nibble)
{
// update the signal
m_signal += s_diff_lookup[m_step * 16 + (nibble & 15)];
// clamp to the maximumf
if (m_signal > 32767)
m_signal = 32767;
else if (m_signal < -32768)
m_signal = -32768;
// adjust the step size and clamp
m_step += s_index_shift[nibble & 7];
if (m_step > 88)
m_step = 88;
else if (m_step < 0)
m_step = 0;
// return the signal
return m_signal;
}
//-------------------------------------------------
// save - save current ADPCM state to buffer
//-------------------------------------------------
void ima_adpcm_state::save()
{
if (!m_saved)
{
m_loop_signal = m_signal;
m_loop_step = m_step;
m_saved = true;
}
}
//-------------------------------------------------
// restore - restore previous ADPCM state
// from buffer
//-------------------------------------------------
void ima_adpcm_state::restore()
{
m_signal = m_loop_signal;
m_step = m_loop_step;
}
//-------------------------------------------------
// compute_tables - precompute tables for faster
// sound generation
//-------------------------------------------------
void ima_adpcm_state::compute_tables()
{
// skip if we already did it
if (s_tables_computed)
return;
s_tables_computed = true;
// nibble to bit map
static const int8_t nbl2bit[16][4] =
{
{ 1, 0, 0, 0}, { 1, 0, 0, 1}, { 1, 0, 1, 0}, { 1, 0, 1, 1},
{ 1, 1, 0, 0}, { 1, 1, 0, 1}, { 1, 1, 1, 0}, { 1, 1, 1, 1},
{-1, 0, 0, 0}, {-1, 0, 0, 1}, {-1, 0, 1, 0}, {-1, 0, 1, 1},
{-1, 1, 0, 0}, {-1, 1, 0, 1}, {-1, 1, 1, 0}, {-1, 1, 1, 1}
};
// loop over all possible steps
for (int step = -8; step <= 80; step++)
{
// compute the step value
int stepval = std::min(floor(16.0 * pow(11.0 / 10.0, (double)step)), 32767.);
// manual correction of some early values
if (step == -5 || step == -4)
stepval++;
// loop over all nibbles and compute the difference
for (int nib = 0; nib < 16; nib++)
{
s_diff_lookup[(step + 8)*16 + nib] = nbl2bit[nib][0] *
(stepval * nbl2bit[nib][1] +
stepval/2 * nbl2bit[nib][2] +
stepval/4 * nbl2bit[nib][3] +
stepval/8);
}
}
}
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