pcsx2/plugins/spu2ghz/mixer.cpp

//GiGaHeRz's SPU2 Driver
//Copyright (c) 2003-2008, David Quintana <gigaherz@gmail.com>
//
//This library is free software; you can redistribute it and/or
//modify it under the terms of the GNU Lesser General Public
//License as published by the Free Software Foundation; either
//version 2.1 of the License, or (at your option) any later version.
//
//This library 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
//Lesser General Public License for more details.
//
//You should have received a copy of the GNU Lesser General Public
//License along with this library; if not, write to the Free Software
//Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
//

// [Air] Notes ----->
//  Adding 'static' to the __forceinline methods hints to the linker that it need not
//  actually include procedural versions of the methods in the DLL.  Under normal circumstances
//  the compiler will still generate the procedures even though they are never used (the inline
//  code is used instead).  Using static reduced the size of my generated .DLL by a few KB.
//   (doesn't really make anything faster, but eh... whatever :)
//
#include "spu2.h"

#include <assert.h>
#include <math.h>
#include <float.h>
#include "lowpass.h"

extern void	spdif_update();

void ADMAOutLogWrite(void *lpData, u32 ulSize);

extern void VoiceStop(int core,int vc);

double pow_2_31 = pow(2.0,31.0);

LPF_data L,R;

extern u32 core;

u32 core, voice;

extern u8 callirq;

double srate_pv=1.0;

extern u32 PsxRates[160];

static const s32 ADSR_MAX_VOL = 0x7fffffff;
static const s32 SPU2_DYN_MEMLINE = 0x3600;

// Performs a 64-bit multiplication between two values and returns the
// high 32 bits as a result (discarding the fractional 32 bits).
// The combined fracional bits of both inputs must be 32 bits for this
// to work properly.
//
// This is meant to be a drop-in replacement for times when the 'div' part
// of a MulDiv is a constant.  (example: 1<<8, or 4096, etc)
//
// [Air] Performance breakdown: This is over 10 times faster than MulDiv in
//   a *worst case* scenario.  It's also more accurate since it forces the
//   caller to  extend the inputs so that they make use of all 32 bits of
//   precision.
//
static s32 __forceinline MulShr32( s32 srcval, s32 mulval )
{
	s64 tmp = ((s64)srcval * mulval );
	return ((s32*)&tmp)[1];

	// Performance note: Using the temp var and memory reference
	// actually ends up being roughly 2x faster than using a bitshift.
	// It won't fly on big endian machines though... :)
}

static s32 __forceinline MulShr32su( s32 srcval, u32 mulval )
{
 	s64 tmp = ((s64)srcval * (s32)mulval );
	return ((s32*)&tmp)[1];
}


void InitADSR()                                    // INIT ADSR
{
	for (int i=0; i<(32+128); i++)
		{
			int shift=(i-32)>>2;
			s64 rate=(i&3)+4;
			if (shift<0)
			{
				rate>>=-shift;
			} else
			{
				rate<<=shift;
			}
			PsxRates[i]=(int)min(rate,0x3fffffff);
		}
}

#define VOL(x) (((s32)x)) //24.8 volume

/////////////////////////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////////////////
//                                                                                     //

const s32 f[5][2] ={{    0,   0 },
					{   60,   0 },
					{  115, -52 },
					{   98, -55 },
					{  122, -60 }};

static void __forceinline XA_decode_block(s16* buffer, const s16* block, s32& prev1, s32& prev2)
{
	const s32 header = *block;
	s32 shift =  ((header>> 0)&0xF)+16;
	s32 pred1 = f[(header>> 4)&0xF][0];
	s32 pred2 = f[(header>> 4)&0xF][1];

	const s8* blockbytes = (s8*)&block[1];

	for(int i=0; i<14; i++, blockbytes++)
	{
		s32 pcm, pcm2;
		{
			s32 data = ((*blockbytes)<<28) & 0xF0000000;
			pcm = data>>shift;
			pcm+=((pred1*prev1)+(pred2*prev2))>>6;
			if(pcm> 32767) pcm= 32767;
			if(pcm<-32768) pcm=-32768;
			*(buffer++) = pcm;
		}

		//prev2=prev1;
		//prev1=pcm;

		{
			s32 data = ((*blockbytes)<<24) & 0xF0000000;
			pcm2 = data>>shift;
			pcm2+=((pred1*pcm)+(pred2*prev1))>>6;
			if(pcm2> 32767) pcm2= 32767;
			if(pcm2<-32768) pcm2=-32768;
			*(buffer++) = pcm2;
		}

		prev2=pcm;
		prev1=pcm2;
	}
}

static void __forceinline XA_decode_block_unsaturated(s16* buffer, const s16* block, s32& prev1, s32& prev2)
{
	const s32 header = *block;
	s32 shift =  ((header>> 0)&0xF)+16;
	s32 pred1 = f[(header>> 4)&0xF][0];
	s32 pred2 = f[(header>> 4)&0xF][1];

	const s8* blockbytes = (s8*)&block[1];

	for(int i=0; i<14; i++, blockbytes++)
	{
		s32 pcm, pcm2;
		{
			s32 data = ((*blockbytes)<<28) & 0xF0000000;
			pcm = data>>shift;
			pcm+=((pred1*prev1)+(pred2*prev2))>>6;
			// [Air] : Fast method, no saturation is performed.
			*(buffer++) = pcm;
		}

		{
			s32 data = ((*blockbytes)<<24) & 0xF0000000;
			pcm2 = data>>shift;
			pcm2+=((pred1*pcm)+(pred2*prev1))>>6;
			// [Air] : Fast method, no saturation is performed.
			*(buffer++) = pcm2;
		}

		prev2=pcm;
		prev1=pcm2;
	}
}

static void __forceinline IncrementNextA( const V_Core& thiscore, V_Voice& vc )
{
	if((vc.NextA==thiscore.IRQA)&&(thiscore.IRQEnable)) { 
		#ifndef PUBLIC
		ConLog(" * SPU2: IRQ Called (IRQ passed).\n"); 
		#endif
		Spdif.Info=4<<core;
		SetIrqCall();
	}

	vc.NextA++;
	vc.NextA&=0xFFFFF;
}


u32 *pcm_cache_flags=NULL;
s16 *pcm_cache_data=NULL;

#ifndef PUBLIC
int g_counter_cache_hits=0;
int g_counter_cache_misses=0;
int g_counter_cache_ignores=0;
#endif

#define XAFLAG_LOOP_END		(1ul<<0)
#define XAFLAG_LOOP			(1ul<<1)
#define XAFLAG_LOOP_START	(1ul<<2)

static void __forceinline __fastcall GetNextDataBuffered( V_Core& thiscore, V_Voice& vc, s32& Data) 
{
	if (vc.SCurrent<28)
	{
		// [Air] : skip the increment?
		//    (witness one of the rare ideal uses of a goto statement!)
		if( (vc.SCurrent&3) != 3 ) goto _skipIncrement;
	}
	else
	{
		if(vc.LoopFlags & XAFLAG_LOOP_END)
		{
			if(vc.LoopFlags & XAFLAG_LOOP)
			{
				vc.NextA=vc.LoopStartA;
			}
			else
			{
				VoiceStop(core,voice);
				thiscore.Regs.ENDX|=1<<voice;
				#ifndef PUBLIC
				if(MsgVoiceOff()) ConLog(" * SPU2: Voice Off by EndPoint: %d \n", voice);
				DebugCores[core].Voices[voice].lastStopReason = 1;
				#endif
			}
		}

		// We'll need the loop flags and buffer pointers regardless of cache status:
		// Note to Self : NextA addresses WORDS (not bytes).

		s16* memptr = GetMemPtr(vc.NextA&0xFFFFF);
		vc.LoopFlags = *memptr >> 8;	// grab loop flags from the upper byte.
		int nexta = vc.NextA >> 3;		// 8 words per encoded block.
		
		vc.SBuffer = &pcm_cache_data[nexta * 28];

		const u32 flagbitmask = 1ul<<(nexta & 31);  // 32 flags per array entry
		nexta >>= 5;

		if( pcm_cache_flags[nexta] & flagbitmask )
		{
			// Cached block!  Read from the cache directly (ie, do nothing)

			#ifndef PUBLIC
			g_counter_cache_hits++;
			#endif
		}
		else
		{
			// Only flag the cache if it's a non-dynamic memory range.
			if( nexta >= (SPU2_DYN_MEMLINE / (8*32)) )
				pcm_cache_flags[nexta] |= flagbitmask;

			#ifndef PUBLIC
			if( nexta < (SPU2_DYN_MEMLINE / (8*32)) )
				g_counter_cache_ignores++;
			else
				g_counter_cache_misses++;
			#endif

			// saturated decoder

			XA_decode_block(vc.SBuffer, memptr, vc.Prev1, vc.Prev2);

			// [Air]: Testing use of a new unsaturated decoder. (benchmark needed)
			//   Chances are the saturation isn't needed, but for a very few exception games.
			//   This is definitely faster than the above version, but is it by enough to
			//   merit possible lower compatibility?  Especially now that games that make
			//   heavy use of the SPU2 via music or sfx will mostly use the cache anyway.

			//XA_decode_block_unsaturated( vc.SBuffer, memptr, vc.Prev1, vc.Prev2 );

			//vc.LoopEnd  =   (data>> 8)&1;
			//vc.Loop     =   (data>> 9)&1;
			//vc.LoopStart=   (data>>10)&1;
		}

		vc.SCurrent = 0;
		if( (vc.LoopFlags & XAFLAG_LOOP_START) && !vc.LoopMode )
		{
			vc.LoopStartA=vc.NextA;
		}

		// [Air] : Increment will get called below (change made to avoid needless code cache clutter)		
		//IncrementNextA( thiscore, vc );
	}

	IncrementNextA( thiscore, vc );

_skipIncrement:
	Data = vc.SBuffer[vc.SCurrent++];
}

/////////////////////////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////////////////
//                                                                                     //

const int InvExpOffsets[] = { 0,4,6,8,9,10,11,12 };

static void __forceinline CalculateADSR( V_Voice& vc ) 
{
	V_ADSR& env(vc.ADSR);

	jASSUME( env.Phase != 0 );

	s32 SLevel = ((s32)env.Sl)<<27;

	jASSUME( SLevel >= 0 );

	if(env.Releasing)
	{
		if( env.Phase < 5)
		{
			env.Phase=5;
		}
	}

	switch (env.Phase)
	{
		case 1: // attack
			if( env.Value == ADSR_MAX_VOL )
			{
				// Already maxed out.  Progress phase and nothing more:
				env.Phase++;
				break;
			}

			if (env.Am) // pseudo exponential
			{
				if (env.Value<0x60000000) // below 75%
				{
					env.Value+=PsxRates[(env.Ar^0x7f)-0x10+32];
				} 
				else // above 75%
				{
					env.Value+=PsxRates[(env.Ar^0x7f)-0x18+32];
				}
			}
			else // linear
			{
				env.Value+=PsxRates[(env.Ar^0x7f)-0x10+32];
			}

			if( env.Value < 0 )
			{
				// We hit the ceiling. 
				env.Phase++;
				env.Value = ADSR_MAX_VOL;
			}

			break;

		case 2: // decay
		{
			u32 off = InvExpOffsets[(env.Value>>28)&7];
			env.Value-=PsxRates[((env.Dr^0x1f)<<2)-0x18+off+32];

			if(env.Value <= SLevel)
			{
				// Clamp decay to SLevel or Zero
				if (env.Value < 0)
					env.Value = 0;
				else
					env.Value = SLevel;

				env.Phase++;
			}

			break;
		}

		case 3: // sustain
			if (env.Sm&2) // decreasing
			{
				if (env.Sm&4) // exponential
				{
					u32 off = InvExpOffsets[(env.Value>>28)&7];
					env.Value-=PsxRates[(env.Sr^0x7f)-0x1b+off+32];
				} 
				else // linear
				{
					env.Value-=PsxRates[(env.Sr^0x7f)-0xf+32];
				}
				if( env.Value <= 0 )
				{
					env.Value = 0;
					env.Phase++;
				}
			} 
			else // increasing
			{
				if (env.Sm&4) // pseudo exponential
				{
					if (env.Value<0x60000000) // below 75%
					{
						env.Value+=PsxRates[(env.Sr^0x7f)-0x10+32];
					} 
					else // above 75%
					{
						env.Value+=PsxRates[(env.Sr^0x7f)-0x18+32];
					}
				}
				else
				{
					// linear

					env.Value+=PsxRates[(env.Sr^0x7f)-0x10+32];
				}

				if( env.Value < 0 )
				{
					env.Value = ADSR_MAX_VOL;
					env.Phase++;
				}
			}

			break;

		case 4: // sustain end
			env.Value = (env.Sm&2) ? 0 : ADSR_MAX_VOL;
			if(env.Value==0)
				env.Phase=6;
			break;

		case 5: // release

			if (env.Rm) // exponential
			{
				u32 off=InvExpOffsets[(env.Value>>28)&7];
				env.Value-=PsxRates[((env.Rr^0x1f)<<2)-0x18+off+32];
			} 
			else // linear
			{
				env.Value-=PsxRates[((env.Rr^0x1f)<<2)-0xc+32];
			}

			if( env.Value <= 0 )
			{
				env.Value=0;
				env.Phase++;
			}

			break;

		case 6: // release end
			env.Value=0;
			break;

		jNO_DEFAULT
	}

	if (env.Phase==6) {
		#ifndef PUBLIC
		if(MsgVoiceOff()) ConLog(" * SPU2: Voice Off by ADSR: %d \n", voice);
		DebugCores[core].Voices[voice].lastStopReason = 2;
		#endif
		VoiceStop(core,voice);
		Cores[core].Regs.ENDX|=(1<<voice);
		env.Phase=0;
	}
}

/////////////////////////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////////////////
//                                                                                     //
static void __forceinline GetNoiseValues(s32& VD) 
{
	static s32 Seed = 0x41595321;

	if(Seed&0x100) VD =(s32)((Seed&0xff)<<8);
	else if(!(Seed&0xffff)) VD = (s32)0x8000;
	else VD = (s32)0x7fff;

	__asm {
		MOV eax,Seed
		ROR eax,5
		XOR eax,0x9a
		MOV ebx,eax
		ROL eax,2
		ADD eax,ebx
		XOR eax,ebx
		ROR eax,3
		MOV Seed,eax
	}
}

/////////////////////////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////////////////
//                                                                                     //

void LowPassFilterInit()
{
	LPF_init(&L,11000,48000);
	LPF_init(&R,11000,48000);
}

void LowPass(s32& VL, s32& VR)
{
	VL = (s32)(LPF(&L,(VL)/pow_2_31)*pow_2_31);
	VR = (s32)(LPF(&R,(VR)/pow_2_31)*pow_2_31);
}

/////////////////////////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////////////////
//                                                                                     //

static void __forceinline UpdatePitch( V_Voice& vc )
{
	s32 pitch;

	// [Air] : re-ordered comparisons: Modulated is much more likely to be zero than voice,
	//   and so the way it was before it's have to check both voice and modulated values
	//   most of the time.  Now it'll just check Modulated and short-circuit past the voice
	//   check (not that it amounts to much, but eh every little bit helps).
	if( (vc.Modulated==0) || (voice==0) )
		pitch=vc.Pitch;
	else
		pitch=(vc.Pitch*(32768 + abs(Cores[core].Voices[voice-1].OutX)))>>15;
	
	vc.SP+=pitch;
}

static void __forceinline GetVoiceValues_Linear(V_Core& thiscore, V_Voice& vc, s32& Value)
{
	while( vc.SP > 0 )
	{
		vc.PV2=vc.PV1;

		GetNextDataBuffered( thiscore, vc, vc.PV1 );

		vc.SP-=4096;
	}

	if( vc.ADSR.Phase==0 )
	{
		Value = 0;
		return;
	}

	CalculateADSR( vc );

	jASSUME( vc.ADSR.Value >= 0 );	// ADSR should never be negative...

	if(Interpolation==0)
	{
		Value = MulShr32( vc.PV1, vc.ADSR.Value );
	} 
	else //if(Interpolation==1) //must be linear
	{
		s32 t0 = vc.PV2 - vc.PV1;
		s32 t1 = vc.PV1;
		Value = MulShr32( t1 - ((t0*vc.SP)>>12), vc.ADSR.Value );
	}
}


static void __forceinline GetVoiceValues_Cubic(V_Core& thiscore, V_Voice& vc, s32& Value)
{
	while( vc.SP > 0 )
	{
		vc.PV4=vc.PV3;
		vc.PV3=vc.PV2;
		vc.PV2=vc.PV1;

		GetNextDataBuffered( thiscore, vc, vc.PV1 );
		vc.PV1<<=3;
		vc.SPc = vc.SP&4095;	// just the fractional part, please!
		vc.SP-=4096;
	}

	if( vc.ADSR.Phase==0 )
	{
		Value = 0;
		return;
	}

	CalculateADSR( vc );

	jASSUME( vc.ADSR.Value >= 0 );	// ADSR should never be negative...

	s32 z0 = vc.PV3 - vc.PV4 + vc.PV1 - vc.PV2;
	s32 z1 = (vc.PV4 - vc.PV3 - z0);
	s32 z2 = (vc.PV2 - vc.PV4);

	s32 mu = vc.SPc;

	s32 val = (z0 * mu) >> 12;
	val = ((val + z1) * mu) >> 12;
	val = ((val + z2) * mu) >> 12;
	val += vc.PV2;

	Value = MulShr32( val, vc.ADSR.Value>>3 );
}

// [Air]: Noise values need to be mixed without going through interpolation, since it
//    can wreak havoc on the noise (causing muffling or popping).
static void __forceinline __fastcall GetNoiseValues(V_Core& thiscore, V_Voice& vc, s32& Data)
{
	while(vc.SP>=4096) 
	{
		GetNoiseValues( Data );
		vc.SP-=4096;
	}

	// GetNoiseValues can't set the phase zero on us unexpectedly
	// like GetVoiceValues can.  Better asster just in case though..
	jASSUME( vc.ADSR.Phase != 0 );	

	CalculateADSR( vc );
}

/////////////////////////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////////////////
//                                                                                     //

void __fastcall ReadInput(V_Core& thiscore, s32& PDataL,s32& PDataR) 
{
	if((thiscore.AutoDMACtrl&(core+1))==(core+1))
	{
		s32 tl,tr;

		if((core==1)&&((PlayMode&8)==8))
		{
			thiscore.InputPos&=~1;

			//CDDA mode
#ifdef PCM24_S1_INTERLEAVE
			*PDataL=*(((s32*)(thiscore.ADMATempBuffer+(thiscore.InputPos<<1))));
			*PDataR=*(((s32*)(thiscore.ADMATempBuffer+(thiscore.InputPos<<1)+2)));
#else
			s32 *pl=(s32*)&(thiscore.ADMATempBuffer[thiscore.InputPos]);
			s32 *pr=(s32*)&(thiscore.ADMATempBuffer[thiscore.InputPos+0x200]);
			PDataL=*pl;
			PDataR=*pr;
#endif

			PDataL>>=4; //give 16.8 data
			PDataR>>=4;

			thiscore.InputPos+=2;
			if((thiscore.InputPos==0x100)||(thiscore.InputPos>=0x200)) {
				thiscore.AdmaInProgress=0;
				if(thiscore.InputDataLeft>=0x200)
				{
					u8 k=thiscore.InputDataLeft>=thiscore.InputDataProgress;

#ifdef PCM24_S1_INTERLEAVE
					AutoDMAReadBuffer(core,1);
#else
					AutoDMAReadBuffer(core,0);
#endif
					thiscore.AdmaInProgress=1;

					thiscore.TSA=(core<<10)+thiscore.InputPos;

					if (thiscore.InputDataLeft<0x200) 
					{
						FileLog("[%10d] AutoDMA%c block end.\n",Cycles, (core==0)?'4':'7');

						#ifndef PUBLIC
						if(thiscore.InputDataLeft>0)
						{
							if(MsgAutoDMA()) ConLog("WARNING: adma buffer didn't finish with a whole block!!\n");
						}
						#endif
						thiscore.InputDataLeft=0;
						thiscore.DMAICounter=1;
					}
				}
				thiscore.InputPos&=0x1ff;
			}

		}
		else if((core==0)&&((PlayMode&4)==4))
		{
			thiscore.InputPos&=~1;

			s32 *pl=(s32*)&(thiscore.ADMATempBuffer[thiscore.InputPos]);
			s32 *pr=(s32*)&(thiscore.ADMATempBuffer[thiscore.InputPos+0x200]);
			PDataL=*pl;
			PDataR=*pr;

			thiscore.InputPos+=2;
			if(thiscore.InputPos>=0x200) {
				thiscore.AdmaInProgress=0;
				if(thiscore.InputDataLeft>=0x200)
				{
					u8 k=thiscore.InputDataLeft>=thiscore.InputDataProgress;

					AutoDMAReadBuffer(core,0);

					thiscore.AdmaInProgress=1;

					thiscore.TSA=(core<<10)+thiscore.InputPos;

					if (thiscore.InputDataLeft<0x200) 
					{
						FileLog("[%10d] Spdif AutoDMA%c block end.\n",Cycles, (core==0)?'4':'7');

						#ifndef PUBLIC
						if(thiscore.InputDataLeft>0)
						{
							if(MsgAutoDMA()) ConLog("WARNING: adma buffer didn't finish with a whole block!!\n");
						}
						#endif
						thiscore.InputDataLeft=0;
						thiscore.DMAICounter=1;
					}
				}
				thiscore.InputPos&=0x1ff;
			}

		}
		else
		{
			if((core==1)&&((PlayMode&2)!=0))
			{
				tl=0;
				tr=0;
			}
			else
			{
				// Using the temporary buffer because this area gets overwritten by some other code.
				//*PDataL=(s32)*(s16*)(spu2mem+0x2000+(core<<10)+thiscore.InputPos);
				//*PDataR=(s32)*(s16*)(spu2mem+0x2200+(core<<10)+thiscore.InputPos);

				tl=(s32)thiscore.ADMATempBuffer[thiscore.InputPos];
				tr=(s32)thiscore.ADMATempBuffer[thiscore.InputPos+0x200];

			}

			PDataL=tl;
			PDataR=tr;

			thiscore.InputPos++;
			if((thiscore.InputPos==0x100)||(thiscore.InputPos>=0x200)) {
				thiscore.AdmaInProgress=0;
				if(thiscore.InputDataLeft>=0x200)
				{
					u8 k=thiscore.InputDataLeft>=thiscore.InputDataProgress;

					AutoDMAReadBuffer(core,0);

					thiscore.AdmaInProgress=1;

					thiscore.TSA=(core<<10)+thiscore.InputPos;

					if (thiscore.InputDataLeft<0x200) 
					{
						thiscore.AutoDMACtrl |= ~3;

						#ifndef PUBLIC
						FileLog("[%10d] AutoDMA%c block end.\n",Cycles, (core==0)?'4':'7');
						if(thiscore.InputDataLeft>0)
						{
							if(MsgAutoDMA()) ConLog("WARNING: adma buffer didn't finish with a whole block!!\n");
						}
						#endif
						thiscore.InputDataLeft=0;
						thiscore.DMAICounter=1;
					}
				}
				thiscore.InputPos&=0x1ff;
			}
		}
	}
	else {
		PDataL=0;
		PDataR=0;
	}
}

/////////////////////////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////////////////
//                                                                                     //

static void __forceinline __fastcall ReadInputPV(V_Core& thiscore, s32& ValL,s32& ValR) 
{
	s32 DL=0, DR=0;

	u32 pitch=AutoDMAPlayRate[core];

	if(pitch==0) pitch=48000;
	
	thiscore.ADMAPV+=pitch;
	while(thiscore.ADMAPV>=48000) 
	{
		ReadInput(thiscore, DL,DR);
		thiscore.ADMAPV-=48000;
		thiscore.ADMAPL=DL;
		thiscore.ADMAPR=DR;
	}

	ValL=thiscore.ADMAPL;
	ValR=thiscore.ADMAPR;

	#ifndef PUBLIC
	s32 InputPeak = max(abs(ValL),abs(ValR));
	if(DebugCores[core].AutoDMAPeak<InputPeak) DebugCores[core].AutoDMAPeak=InputPeak;
	#endif

	// Apply volumes:
	ValL *= thiscore.InpL;
	ValR *= thiscore.InpR;
	ValL >>= 1;
	ValR >>= 1;

}

/////////////////////////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////////////////
//                                                                                     //

#define VOLFLAG_REVERSE_PHASE	(1ul<<0)
#define VOLFLAG_DECREMENT		(1ul<<1)
#define VOLFLAG_EXPONENTIAL		(1ul<<2)
#define VOLFLAG_SLIDE_ENABLE	(1ul<<3)

static void __fastcall UpdateVolume(V_Volume& Vol)
{
	// TIMINGS ARE FAKE!!! Need to investigate.

	// [Air]: Cleaned up this code... may have broken it.  Can't really
	//   test it here since none of my games seem to use it.  If anything's
	//   not sounding right, we should revert the code in this method first.

	// [Air] Reverse phasing?
	//   Invert our value so that exponential mathematics are applied
	//   as if the volume were sliding the other direction.  This makes
	//   a lot more sense than the old method's likeliness to chop off
	//   sound volumes to zero abruptly.

	if(Vol.Mode & VOLFLAG_REVERSE_PHASE)
	{
		ConLog( " *** SPU2 > Reverse Phase in progress!\n" );
		Vol.Value = 0x7fff - Vol.Value;
	}

	if (Vol.Mode & VOLFLAG_DECREMENT)
	{
		// Decrement

		if(Vol.Mode & VOLFLAG_EXPONENTIAL)
		{
			ConLog( " *** SPU2 > Exponential Volume Slide Down!\n" );
			Vol.Value *= Vol.Increment >> 7;
			Vol.Value-=((32768*5)>>(Vol.Increment));
		}
		else
		{
			Vol.Value-=Vol.Increment;
		}

		if (Vol.Value<0)
		{
			Vol.Value = 0;
			Vol.Mode=0;	// disable slide
		}
	}
	else
	{
		//ConLog( " *** SPU2 > Volflag > Increment!\n" );
		// Increment
		if(Vol.Mode & VOLFLAG_EXPONENTIAL)
		{
			ConLog( " *** SPU2 > Exponential Volume Slide Up!\n" );
			int T = Vol.Increment>>(Vol.Value>>12);
			Vol.Value+=T;
		}
		else
		{
			Vol.Value+=Vol.Increment;
		}

		if( Vol.Value > 0x7fff )
		{
			Vol.Value = 0x7fff;
			Vol.Mode=0; // disable slide
		}
	}

	// Reverse phasing
	//  Invert the value back into output form:
	if(Vol.Mode & VOLFLAG_REVERSE_PHASE) Vol.Value = 0x7fff-Vol.Value;

	//Vol.Value=NVal;
}

/////////////////////////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////////////////
//                                                                                     //

static s32 __forceinline clamp(s32 x)
{
	if (x>0x00ffffff)  return 0x00ffffff;
	if (x<0xff000000)  return 0xff000000;
	return x;
}

/////////////////////////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////////////////
//                                                                                     //

static void DoReverb( V_Core& thiscore, s32& OutL, s32& OutR, s32 InL, s32 InR)
{
	static s32 INPUT_SAMPLE_L,INPUT_SAMPLE_R;
	static s32 OUTPUT_SAMPLE_L,OUTPUT_SAMPLE_R;

	if(!(thiscore.FxEnable&&EffectsEnabled))
	{
		OUTPUT_SAMPLE_L=0;
		OUTPUT_SAMPLE_R=0;
	}
	else if((Cycles&1)==0) 
	{
		INPUT_SAMPLE_L=InL;
		INPUT_SAMPLE_R=InR;
	}
	else  
	{
/////////////////////////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////////////////
		s32 IIR_INPUT_A0,IIR_INPUT_A1,IIR_INPUT_B0,IIR_INPUT_B1;
		s32 ACC0,ACC1;
		s32 FB_A0,FB_A1,FB_B0,FB_B1;
		s32 buffsize=thiscore.EffectsEndA-thiscore.EffectsStartA+1;

		if(buffsize<0)
		{
			buffsize = thiscore.EffectsEndA;
			thiscore.EffectsEndA=thiscore.EffectsStartA;
			thiscore.EffectsStartA=buffsize;
			buffsize=thiscore.EffectsEndA-thiscore.EffectsStartA+1;
		}

		//filter the 2 samples (prev then current)
		LowPass(INPUT_SAMPLE_L, INPUT_SAMPLE_R);
		LowPass(InL, InR);

		INPUT_SAMPLE_L=(INPUT_SAMPLE_L+InL)>>9;
		INPUT_SAMPLE_R=(INPUT_SAMPLE_R+InR)>>9;

#define BUFFER(x)	((s32)(*GetMemPtr(thiscore.EffectsStartA + ((thiscore.ReverbX + buffsize-((x)<<2))%buffsize))))
#define SBUFFER(x)	(*GetMemPtr(thiscore.EffectsStartA + ((thiscore.ReverbX + buffsize-((x)<<2))%buffsize)))
		
		thiscore.ReverbX=((thiscore.ReverbX + 4)%buffsize);

		IIR_INPUT_A0 = (BUFFER(thiscore.Revb.IIR_SRC_A0) * thiscore.Revb.IIR_COEF + INPUT_SAMPLE_L * thiscore.Revb.IN_COEF_L)>>16;
		IIR_INPUT_A1 = (BUFFER(thiscore.Revb.IIR_SRC_A1) * thiscore.Revb.IIR_COEF + INPUT_SAMPLE_R * thiscore.Revb.IN_COEF_R)>>16;
		IIR_INPUT_B0 = (BUFFER(thiscore.Revb.IIR_SRC_B0) * thiscore.Revb.IIR_COEF + INPUT_SAMPLE_L * thiscore.Revb.IN_COEF_L)>>16;
		IIR_INPUT_B1 = (BUFFER(thiscore.Revb.IIR_SRC_B1) * thiscore.Revb.IIR_COEF + INPUT_SAMPLE_R * thiscore.Revb.IN_COEF_R)>>16;

		SBUFFER(thiscore.Revb.IIR_DEST_A0 + 4) = clamp((IIR_INPUT_A0 * thiscore.Revb.IIR_ALPHA + BUFFER(thiscore.Revb.IIR_DEST_A0) * (65535 - thiscore.Revb.IIR_ALPHA))>>16);
		SBUFFER(thiscore.Revb.IIR_DEST_A1 + 4) = clamp((IIR_INPUT_A1 * thiscore.Revb.IIR_ALPHA + BUFFER(thiscore.Revb.IIR_DEST_A1) * (65535 - thiscore.Revb.IIR_ALPHA))>>16);
		SBUFFER(thiscore.Revb.IIR_DEST_B0 + 4) = clamp((IIR_INPUT_B0 * thiscore.Revb.IIR_ALPHA + BUFFER(thiscore.Revb.IIR_DEST_B0) * (65535 - thiscore.Revb.IIR_ALPHA))>>16);
		SBUFFER(thiscore.Revb.IIR_DEST_B1 + 4) = clamp((IIR_INPUT_B1 * thiscore.Revb.IIR_ALPHA + BUFFER(thiscore.Revb.IIR_DEST_B1) * (65535 - thiscore.Revb.IIR_ALPHA))>>16);

		ACC0 = (s32)(BUFFER(thiscore.Revb.ACC_SRC_A0) * thiscore.Revb.ACC_COEF_A +
				BUFFER(thiscore.Revb.ACC_SRC_B0) * thiscore.Revb.ACC_COEF_B +
				BUFFER(thiscore.Revb.ACC_SRC_C0) * thiscore.Revb.ACC_COEF_C +
				BUFFER(thiscore.Revb.ACC_SRC_D0) * thiscore.Revb.ACC_COEF_D)>>16;
		ACC1 = (s32)(BUFFER(thiscore.Revb.ACC_SRC_A1) * thiscore.Revb.ACC_COEF_A +
				BUFFER(thiscore.Revb.ACC_SRC_B1) * thiscore.Revb.ACC_COEF_B +
				BUFFER(thiscore.Revb.ACC_SRC_C1) * thiscore.Revb.ACC_COEF_C +
				BUFFER(thiscore.Revb.ACC_SRC_D1) * thiscore.Revb.ACC_COEF_D)>>16;

		FB_A0 = BUFFER(thiscore.Revb.MIX_DEST_A0 - thiscore.Revb.FB_SRC_A);
		FB_A1 = BUFFER(thiscore.Revb.MIX_DEST_A1 - thiscore.Revb.FB_SRC_A);
		FB_B0 = BUFFER(thiscore.Revb.MIX_DEST_B0 - thiscore.Revb.FB_SRC_B);
		FB_B1 = BUFFER(thiscore.Revb.MIX_DEST_B1 - thiscore.Revb.FB_SRC_B);

		SBUFFER(thiscore.Revb.MIX_DEST_A0) = clamp((ACC0 - FB_A0 * thiscore.Revb.FB_ALPHA)>>16);
		SBUFFER(thiscore.Revb.MIX_DEST_A1) = clamp((ACC1 - FB_A1 * thiscore.Revb.FB_ALPHA)>>16);
		SBUFFER(thiscore.Revb.MIX_DEST_B0) = clamp(((thiscore.Revb.FB_ALPHA * ACC0) - FB_A0 * (65535 - thiscore.Revb.FB_ALPHA) - FB_B0 * thiscore.Revb.FB_X)>>16);
		SBUFFER(thiscore.Revb.MIX_DEST_B1) = clamp(((thiscore.Revb.FB_ALPHA * ACC1) - FB_A1 * (65535 - thiscore.Revb.FB_ALPHA) - FB_B1 * thiscore.Revb.FB_X)>>16);

		OUTPUT_SAMPLE_L=clamp((BUFFER(thiscore.Revb.MIX_DEST_A0)+BUFFER(thiscore.Revb.MIX_DEST_B0))>>2);
		OUTPUT_SAMPLE_R=clamp((BUFFER(thiscore.Revb.MIX_DEST_B1)+BUFFER(thiscore.Revb.MIX_DEST_B1))>>2);
	} 
	OutL=OUTPUT_SAMPLE_L;
	OutR=OUTPUT_SAMPLE_R;
}

/////////////////////////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////////////////
//                                                                                     //
bool inited = false;
s32 count=0;
s32 maxpeak=0;
double rfactor=1;
double cfactor=1;
double diff=0;

static __forceinline s32 ApplyVolume(s32 data, s32 volume)
{
	return (volume * data);
}

// writes a signed value to the SPU2 ram
// Performs no cache invalidation -- use only for dynamic memory ranges
// of the SPU2 (between 0x0000 and SPU2_DYN_MEMLINE)
static __forceinline void spu2M_WriteFast( u32 addr, s16 value )
{
	// throw an assertion if the memory range is invalid:
	jASSUME( addr < SPU2_DYN_MEMLINE );
	*GetMemPtr( addr ) = value;
}


static __forceinline void MixVoice( V_Core& thiscore, V_Voice& vc, s32& VValL, s32& VValR )
{
	s32 Value=0;

	VValL=0;
	VValR=0;

	// [Air] : Most games don't use much volume slide effects.  So only
	//   call the UpdateVolume methods when needed by checking the flag
	//   outside the method here...

	if( vc.VolumeL.Mode & VOLFLAG_SLIDE_ENABLE ) UpdateVolume( vc.VolumeL );
	if( vc.VolumeR.Mode & VOLFLAG_SLIDE_ENABLE ) UpdateVolume( vc.VolumeR );

	if (vc.ADSR.Phase>0) 
	{
		UpdatePitch( vc );

		if( vc.Noise )
			GetNoiseValues( thiscore, vc, Value );
		else
		{
			if( Interpolation == 2 )
				GetVoiceValues_Cubic( thiscore, vc, Value );
			else
				GetVoiceValues_Linear( thiscore, vc, Value );
		}

		// Record the output (used for modulation effects)
		vc.OutX = Value;

		#ifndef PUBLIC
		DebugCores[core].Voices[voice].displayPeak = max(DebugCores[core].Voices[voice].displayPeak,abs(Value));
		#endif

		VValL=ApplyVolume(Value,(vc.VolumeL.Value));
		VValR=ApplyVolume(Value,(vc.VolumeR.Value));
	}

	if (voice==1)      spu2M_WriteFast( 0x400 + (core<<12) + OutPos, (s16)Value );
	else if (voice==3) spu2M_WriteFast( 0x600 + (core<<12) + OutPos, (s16)Value );

}


static void __fastcall MixCore(s32& OutL, s32& OutR, s32 ExtL, s32 ExtR)
{
	s32 RVL,RVR;
	s32 SDL=0,SDR=0;
	s32 SWL=0,SWR=0;

	V_Core& thiscore( Cores[core] );

	for (voice=0;voice<24;voice++) 
	{
		s32 VValL,VValR;

		V_Voice& vc( thiscore.Voices[voice] );
		MixVoice( thiscore, vc, VValL, VValR );

		SDL += VValL * vc.DryL;
		SDR += VValR * vc.DryR;
		SWL += VValL * vc.WetL;
		SWR += VValR * vc.WetR;
	}

	//Write To Output Area
	spu2M_WriteFast( 0x1000 + (core<<12) + OutPos, (s16)(SDL>>16) );
	spu2M_WriteFast( 0x1200 + (core<<12) + OutPos, (s16)(SDR>>16) );
	spu2M_WriteFast( 0x1400 + (core<<12) + OutPos, (s16)(SWL>>16) );
	spu2M_WriteFast( 0x1600 + (core<<12) + OutPos, (s16)(SWR>>16) );

	s32 TDL,TDR;

	// Mix in the Input data
	TDL = OutL * thiscore.InpDryL;
	TDR = OutR * thiscore.InpDryR;

	// Mix in the Voice data
	TDL += SDL * thiscore.SndDryL;
	TDR += SDR * thiscore.SndDryR;

	// Mix in the External (nothing/core0) data
	TDL += ExtL * thiscore.ExtDryL;
	TDR += ExtR * thiscore.ExtDryR;
	
	if(EffectsEnabled)
	{
		s32 TWL=0,TWR=0;

		// Mix Input, Voice, and External data:
		TWL = OutL * thiscore.InpWetL;
		TWR = OutR * thiscore.InpWetR;
		TWL += SWL * thiscore.SndWetL;
		TWR += SWR * thiscore.SndWetR;
		TWL += ExtL * thiscore.ExtWetL; 
		TWR += ExtR * thiscore.ExtWetR;

		//Apply Effects
		DoReverb( thiscore, RVL,RVR,TWL>>16,TWR>>16);

		TWL=ApplyVolume(RVL,VOL(thiscore.FxL));
		TWR=ApplyVolume(RVR,VOL(thiscore.FxR));

		//Mix Wet,Dry
		OutL=(TDL + TWL);
		OutR=(TDR + TWR);
	}
	else
	{
		OutL = TDL;
		OutR = TDR;
	}

	//Apply Master Volume
	if( thiscore.MasterL.Mode & VOLFLAG_SLIDE_ENABLE )  UpdateVolume(thiscore.MasterL);
	if( thiscore.MasterR.Mode & VOLFLAG_SLIDE_ENABLE )  UpdateVolume(thiscore.MasterR);

	if (thiscore.Mute==0)
	{
		OutL = MulShr32( OutL, ((s32)thiscore.MasterL.Value)<<16 );
		OutR = MulShr32( OutR, ((s32)thiscore.MasterR.Value)<<16 );
	}
	else 
	{
		OutL=0;
		OutR=0;
	}
}

// used to throttle the output rate of cache stat reports
static int p_cachestat_counter=0;

void __fastcall Mix() 
{
	s32 ExtL=0, ExtR=0, OutL, OutR;

	// ****  CORE ZERO  ****

	core=0;
	if( (PlayMode&4) != 4 )
	{
		// get input data from input buffers
		ReadInputPV(Cores[0], ExtL, ExtR);
	}

	MixCore( ExtL, ExtR, 0, 0 );

	if( PlayMode & 4 )
	{
		ExtL=0;
		ExtR=0;
	}

	// Commit Core 0 output to ram before mixing Core 1:
	ExtL>>=13;
	ExtR>>=13;
	spu2M_WriteFast( 0x800 + OutPos, ExtL>>3 );
	spu2M_WriteFast( 0xA00 + OutPos, ExtR>>3 );

	// ****  CORE ONE  ****

	core=1;
	if( (PlayMode&8) != 8 )
	{
		ReadInputPV(Cores[1], OutL, OutR);	// get input data from input buffers
	}

	// Apply volume to the external (Core 0) input data.

	MixCore( OutL, OutR, ExtL*Cores[1].ExtL, ExtR*Cores[1].ExtR );

	if( PlayMode & 8 )
	{
		ReadInput(Cores[1], OutL, OutR);
	}

#ifndef PUBLIC
	static s32 Peak0,Peak1;
	static s32 PCount;

	Peak0 = max(Peak0,max(ExtL,ExtR));
	Peak1 = max(Peak1,max(OutL,OutR));
#endif

	// [Air] : Removed MulDiv here in favor of a more direct approach
	//   within the SndOut driver (which ends up having to apply its own
	//   master volume divisors anyway).
	//ExtL=MulDiv(OutL,VolumeMultiplier,1<<6);
	//ExtR=MulDiv(OutR,VolumeMultiplier,1<<6);

	// Update spdif (called each sample)
	if(PlayMode&4)
	{
		spdif_update();
	}

	// AddToBuffer
	SndWrite(OutL, OutR); //ExtL,ExtR);
	OutPos++;
	if (OutPos>=0x200) OutPos=0;

#ifndef PUBLIC
	// [TODO]: Create an INI option to enable/disable this particular log.
	p_cachestat_counter++;
	if(p_cachestat_counter > (48000*10) )
	{
		p_cachestat_counter = 0;
		if( MsgCache() ) ConLog( " * SPU2 > CacheStats > Hits: %d  Misses: %d  Ignores: %d\n",
			g_counter_cache_hits,
			g_counter_cache_misses,
			g_counter_cache_ignores );

		g_counter_cache_hits = 
		g_counter_cache_misses =
		g_counter_cache_ignores = 0;
	}
#endif
}

/////////////////////////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////////////////
//                                                                                     //
u32 PsxRates[160]={
	
	//for +Lin: PsxRates[value+8]
	//for -Lin: PsxRates[value+7]

	0xFFFFFFFF,0xFFFFFFFF,0xFFFFFFFF,0xFFFFFFFF,0xFFFFFFFF,0xFFFFFFFF,0xFFFFFFFF,0xFFFFFFFF,
	0xD744FCCB,0xB504F334,0x9837F052,0x80000000,0x6BA27E65,0x5A82799A,0x4C1BF829,0x40000000,
	0x35D13F33,0x2D413CCD,0x260DFC14,0x20000000,0x1AE89F99,0x16A09E66,0x1306FE0A,0x10000000,
	0x0D744FCD,0x0B504F33,0x09837F05,0x08000000,0x06BA27E6,0x05A8279A,0x04C1BF83,0x04000000,
	0x035D13F3,0x02D413CD,0x0260DFC1,0x02000000,0x01AE89FA,0x016A09E6,0x01306FE1,0x01000000,
	0x00D744FD,0x00B504F3,0x009837F0,0x00800000,0x006BA27E,0x005A827A,0x004C1BF8,0x00400000,
	0x0035D13F,0x002D413D,0x00260DFC,0x00200000,0x001AE8A0,0x0016A09E,0x001306FE,0x00100000,
	0x000D7450,0x000B504F,0x0009837F,0x00080000,0x0006BA28,0x0005A828,0x0004C1C0,0x00040000,
	0x00035D14,0x0002D414,0x000260E0,0x00020000,0x0001AE8A,0x00016A0A,0x00013070,0x00010000,
	0x0000D745,0x0000B505,0x00009838,0x00008000,0x00006BA2,0x00005A82,0x00004C1C,0x00004000,
	0x000035D1,0x00002D41,0x0000260E,0x00002000,0x00001AE9,0x000016A1,0x00001307,0x00001000,
	0x00000D74,0x00000B50,0x00000983,0x00000800,0x000006BA,0x000005A8,0x000004C2,0x00000400,
	0x0000035D,0x000002D4,0x00000261,0x00000200,0x000001AF,0x0000016A,0x00000130,0x00000100,
	0x000000D7,0x000000B5,0x00000098,0x00000080,0x0000006C,0x0000005B,0x0000004C,0x00000040,
	0x00000036,0x0000002D,0x00000026,0x00000020,0x0000001B,0x00000017,0x00000013,0x00000010,
	0x0000000D,0x0000000B,0x0000000A,0x00000008,0x00000007,0x00000006,0x00000005,0x00000004,
	0x00000003,0x00000003,0x00000002,0x00000002,0x00000002,0x00000001,0x00000001,0x00000000,

	//128+8
	0x00000000,0x00000000,0x00000000,0x00000000,0x00000000,0x00000000,0x00000000,0x00000000,
};

/////////////////////////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////////////////
//                                                                                     //

/*
-----------------------------------------------------------------------------
PSX reverb hardware notes
by Neill Corlett
-----------------------------------------------------------------------------

Yadda yadda disclaimer yadda probably not perfect yadda well it's okay anyway
yadda yadda.

-----------------------------------------------------------------------------

Basics
------

- The reverb buffer is 22khz 16-bit mono PCM.
- It starts at the reverb address given by 1DA2, extends to
  the end of sound RAM, and wraps back to the 1DA2 address.

Setting the address at 1DA2 resets the current reverb work address.

This work address ALWAYS increments every 1/22050 sec., regardless of
whether reverb is enabled (bit 7 of 1DAA set).

And the contents of the reverb buffer ALWAYS play, scaled by the
"reverberation depth left/right" volumes (1D84/1D86).
(which, by the way, appear to be scaled so 3FFF=approx. 1.0, 4000=-1.0)

-----------------------------------------------------------------------------

Register names
--------------

These are probably not their real names.
These are probably not even correct names.
We will use them anyway, because we can.

1DC0: FB_SRC_A       (offset)
1DC2: FB_SRC_B       (offset)
1DC4: IIR_ALPHA      (coef.)
1DC6: ACC_COEF_A     (coef.)
1DC8: ACC_COEF_B     (coef.)
1DCA: ACC_COEF_C     (coef.)
1DCC: ACC_COEF_D     (coef.)
1DCE: IIR_COEF       (coef.)
1DD0: FB_ALPHA       (coef.)
1DD2: FB_X           (coef.)
1DD4: IIR_DEST_A0    (offset)
1DD6: IIR_DEST_A1    (offset)
1DD8: ACC_SRC_A0     (offset)
1DDA: ACC_SRC_A1     (offset)
1DDC: ACC_SRC_B0     (offset)
1DDE: ACC_SRC_B1     (offset)
1DE0: IIR_SRC_A0     (offset)
1DE2: IIR_SRC_A1     (offset)
1DE4: IIR_DEST_B0    (offset)
1DE6: IIR_DEST_B1    (offset)
1DE8: ACC_SRC_C0     (offset)
1DEA: ACC_SRC_C1     (offset)
1DEC: ACC_SRC_D0     (offset)
1DEE: ACC_SRC_D1     (offset)
1DF0: IIR_SRC_B1     (offset)
1DF2: IIR_SRC_B0     (offset)
1DF4: MIX_DEST_A0    (offset)
1DF6: MIX_DEST_A1    (offset)
1DF8: MIX_DEST_B0    (offset)
1DFA: MIX_DEST_B1    (offset)
1DFC: IN_COEF_L      (coef.)
1DFE: IN_COEF_R      (coef.)

The coefficients are signed fractional values.
-32768 would be -1.0
 32768 would be  1.0 (if it were possible... the highest is of course 32767)

The offsets are (byte/8) offsets into the reverb buffer.
i.e. you multiply them by 8, you get byte offsets.
You can also think of them as (samples/4) offsets.
They appear to be signed.  They can be negative.
None of the documented presets make them negative, though.

Yes, 1DF0 and 1DF2 appear to be backwards.  Not a typo.

-----------------------------------------------------------------------------

What it does
------------

We take all reverb sources:
- regular channels that have the reverb bit on
- cd and external sources, if their reverb bits are on
and mix them into one stereo 44100hz signal.

Lowpass/downsample that to 22050hz.  The PSX uses a proper bandlimiting
algorithm here, but I haven't figured out the hysterically exact specifics.
I use an 8-tap filter with these coefficients, which are nice but probably
not the real ones:

0.037828187894
0.157538631280
0.321159685278
0.449322115345
0.449322115345
0.321159685278
0.157538631280
0.037828187894

So we have two input samples (INPUT_SAMPLE_L, INPUT_SAMPLE_R) every 22050hz.

* IN MY EMULATION, I divide these by 2 to make it clip less.
  (and of course the L/R output coefficients are adjusted to compensate)
  The real thing appears to not do this.

At every 22050hz tick:
- If the reverb bit is enabled (bit 7 of 1DAA), execute the reverb
  steady-state algorithm described below
- AFTERWARDS, retrieve the "wet out" L and R samples from the reverb buffer
  (This part may not be exactly right and I guessed at the coefs. TODO: check later.)
  L is: 0.333 * (buffer[MIX_DEST_A0] + buffer[MIX_DEST_B0])
  R is: 0.333 * (buffer[MIX_DEST_A1] + buffer[MIX_DEST_B1])
- Advance the current buffer position by 1 sample

The wet out L and R are then upsampled to 44100hz and played at the
"reverberation depth left/right" (1D84/1D86) volume, independent of the main
volume.

-----------------------------------------------------------------------------

Reverb steady-state
-------------------

The reverb steady-state algorithm is fairly clever, and of course by
"clever" I mean "batshit insane".

buffer[x] is relative to the current buffer position, not the beginning of
the buffer.  Note that all buffer offsets must wrap around so they're
contained within the reverb work area.

Clipping is performed at the end... maybe also sooner, but definitely at
the end.

IIR_INPUT_A0 = buffer[IIR_SRC_A0] * IIR_COEF + INPUT_SAMPLE_L * IN_COEF_L;
IIR_INPUT_A1 = buffer[IIR_SRC_A1] * IIR_COEF + INPUT_SAMPLE_R * IN_COEF_R;
IIR_INPUT_B0 = buffer[IIR_SRC_B0] * IIR_COEF + INPUT_SAMPLE_L * IN_COEF_L;
IIR_INPUT_B1 = buffer[IIR_SRC_B1] * IIR_COEF + INPUT_SAMPLE_R * IN_COEF_R;

IIR_A0 = IIR_INPUT_A0 * IIR_ALPHA + buffer[IIR_DEST_A0] * (1.0 - IIR_ALPHA);
IIR_A1 = IIR_INPUT_A1 * IIR_ALPHA + buffer[IIR_DEST_A1] * (1.0 - IIR_ALPHA);
IIR_B0 = IIR_INPUT_B0 * IIR_ALPHA + buffer[IIR_DEST_B0] * (1.0 - IIR_ALPHA);
IIR_B1 = IIR_INPUT_B1 * IIR_ALPHA + buffer[IIR_DEST_B1] * (1.0 - IIR_ALPHA);

buffer[IIR_DEST_A0 + 1sample] = IIR_A0;
buffer[IIR_DEST_A1 + 1sample] = IIR_A1;
buffer[IIR_DEST_B0 + 1sample] = IIR_B0;
buffer[IIR_DEST_B1 + 1sample] = IIR_B1;

ACC0 = buffer[ACC_SRC_A0] * ACC_COEF_A +
       buffer[ACC_SRC_B0] * ACC_COEF_B +
       buffer[ACC_SRC_C0] * ACC_COEF_C +
       buffer[ACC_SRC_D0] * ACC_COEF_D;
ACC1 = buffer[ACC_SRC_A1] * ACC_COEF_A +
       buffer[ACC_SRC_B1] * ACC_COEF_B +
       buffer[ACC_SRC_C1] * ACC_COEF_C +
       buffer[ACC_SRC_D1] * ACC_COEF_D;

FB_A0 = buffer[MIX_DEST_A0 - FB_SRC_A];
FB_A1 = buffer[MIX_DEST_A1 - FB_SRC_A];
FB_B0 = buffer[MIX_DEST_B0 - FB_SRC_B];
FB_B1 = buffer[MIX_DEST_B1 - FB_SRC_B];

buffer[MIX_DEST_A0] = ACC0 - FB_A0 * FB_ALPHA;
buffer[MIX_DEST_A1] = ACC1 - FB_A1 * FB_ALPHA;
buffer[MIX_DEST_B0] = (FB_ALPHA * ACC0) - FB_A0 * (FB_ALPHA^0x8000) - FB_B0 * FB_X;
buffer[MIX_DEST_B1] = (FB_ALPHA * ACC1) - FB_A1 * (FB_ALPHA^0x8000) - FB_B1 * FB_X;

-----------------------------------------------------------------------------
*/