text: //
  //   Copyright (C) 2007 by sinamas <sinamas at users.sourceforge.net>
  //
  //   This program is free software; you can redistribute it and/or modify
  //   it under the terms of the GNU General Public License version 2 as
  //   published by the Free Software Foundation.
  //
  //   This program is distributed in the hope that it will be useful,
  //   but WITHOUT ANY WARRANTY; without even the implied warranty of
  //   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  //   GNU General Public License version 2 for more details.
  //
  //   You should have received a copy of the GNU General Public License
  //   version 2 along with this program; if not, write to the
  //   Free Software Foundation, Inc.,
  //   51 Franklin St, Fifth Floor, Boston, MA  02110-1301, USA.
  //
  
  #include "sound.h"
  #include "savestate.h"
  #include <algorithm>
  #include <cstring>
  
  /*
  	Frame Sequencer
  
  	Step    Length Ctr  Vol Env     Sweep
  	- - - - - - - - - - - - - - - - - - - -
  S0	0       Clock       -           Clock
  S1	1       -           Clock       -
  	2       Clock       -           -
  	3       -           -           -
  	4       Clock       -           Clock
  	5       -           -           -
  	6       Clock       -           -
  	7       -           -           -
  	- - - - - - - - - - - - - - - - - - - -
  	Rate    256 Hz      64 Hz       128 Hz
  
  S0) start step on sound power on.
  S1) step gets immediately incremented at power on if closer to previous edge than next.
  Clock) clock timer on transition to step.
  
  */
  
  namespace gambatte {
  
  PSG::PSG()
  : buffer_(0)
  , bufferPos_(0)
  , lastUpdate_(0)
  , soVol_(0)
  , rsum_(0x8000) // initialize to 0x8000 to prevent borrows from high word, xor away later
  , enabled_(false)
  {
  }
  
  void PSG::init(bool cgb) {
  	ch1_.init(cgb);
  	ch3_.init(cgb);
  }
  
  void PSG::reset() {
  	ch1_.reset();
  	ch2_.reset();
  	ch3_.reset();
  	ch4_.reset();
  }
  
  void PSG::setStatePtrs(SaveState &state) {
  	ch3_.setStatePtrs(state);
  }
  
  void PSG::saveState(SaveState &state) {
  	ch1_.saveState(state);
  	ch2_.saveState(state);
  	ch3_.saveState(state);
  	ch4_.saveState(state);
  }
  
  void PSG::loadState(SaveState const &state) {
  	ch1_.loadState(state);
  	ch2_.loadState(state);
  	ch3_.loadState(state);
  	ch4_.loadState(state);
  
  	lastUpdate_ = state.cpu.cycleCounter;
  	setSoVolume(state.mem.ioamhram.get()[0x124]);
  	mapSo(state.mem.ioamhram.get()[0x125]);
  	enabled_ = state.mem.ioamhram.get()[0x126] >> 7 & 1;
  }
  
  void PSG::accumulateChannels(unsigned long const cycles) {
  	uint_least32_t *const buf = buffer_ + bufferPos_;
  	std::memset(buf, 0, cycles * sizeof *buf);
  	ch1_.update(buf, soVol_, cycles);
  	ch2_.update(buf, soVol_, cycles);
  	ch3_.update(buf, soVol_, cycles);
  	ch4_.update(buf, soVol_, cycles);
  }
  
  void PSG::generateSamples(unsigned long const cycleCounter, bool const doubleSpeed) {
  	unsigned long const cycles = (cycleCounter - lastUpdate_) >> (1 + doubleSpeed);
  	lastUpdate_ += cycles << (1 + doubleSpeed);
  
  	if (cycles)
  		accumulateChannels(cycles);
  
  	bufferPos_ += cycles;
  }
  
  void PSG::resetCounter(unsigned long newCc, unsigned long oldCc, bool doubleSpeed) {
  	generateSamples(oldCc, doubleSpeed);
  	lastUpdate_ = newCc - (oldCc - lastUpdate_);
  }
  
  std::size_t PSG::fillBuffer() {
  	uint_least32_t sum = rsum_;
  	uint_least32_t *b = buffer_;
  	std::size_t n = bufferPos_;
  
  	if (std::size_t n2 = n >> 3) {
  		n -= n2 << 3;
  
  		do {
  			sum += b[0];
  			b[0] = sum ^ 0x8000;
  			sum += b[1];
  			b[1] = sum ^ 0x8000;
  			sum += b[2];
  			b[2] = sum ^ 0x8000;
  			sum += b[3];
  			b[3] = sum ^ 0x8000;
  			sum += b[4];
  			b[4] = sum ^ 0x8000;
  			sum += b[5];
  			b[5] = sum ^ 0x8000;
  			sum += b[6];
  			b[6] = sum ^ 0x8000;
  			sum += b[7];
  			b[7] = sum ^ 0x8000;
  
  			b += 8;
  		} while (--n2);
  	}
  
  	while (n--) {
  		sum += *b;
  		// xor away the initial rsum value of 0x8000 (which prevents
  		// borrows from the high word) from the low word
  		*b++ = sum ^ 0x8000;
  	}
  
  	rsum_ = sum;
  
  	return bufferPos_;
  }
  
  static bool isBigEndianSampleOrder() {
  	union {
  		uint_least32_t ul32;
  		unsigned char uc[sizeof(uint_least32_t)];
  	} u;
  	u.ul32 = -0x10000;
  	return u.uc[0];
  }
  
  static unsigned long so1Mul() { return isBigEndianSampleOrder() ? 0x00000001 : 0x00010000; }
  static unsigned long so2Mul() { return isBigEndianSampleOrder() ? 0x00010000 : 0x00000001; }
  
  void PSG::setSoVolume(unsigned nr50) {
  	soVol_ = ((nr50      & 0x7) + 1) * so1Mul() * 64
  	       + ((nr50 >> 4 & 0x7) + 1) * so2Mul() * 64;
  }
  
  void PSG::mapSo(unsigned nr51) {
  	unsigned long so = nr51 * so1Mul() + (nr51 >> 4) * so2Mul();
  	ch1_.setSo((so      & 0x00010001) * 0xFFFF);
  	ch2_.setSo((so >> 1 & 0x00010001) * 0xFFFF);
  	ch3_.setSo((so >> 2 & 0x00010001) * 0xFFFF);
  	ch4_.setSo((so >> 3 & 0x00010001) * 0xFFFF);
  }
  
  unsigned PSG::getStatus() const {
  	return ch1_.isActive()
  	     | ch2_.isActive() << 1
  	     | ch3_.isActive() << 2
  	     | ch4_.isActive() << 3;
  }
  
  }
  