Interpolation algorithm uses neighbor sample - so we can optimize
ADPCM channel process to use last decoded values. We can rid of "nxt*" variables and second adpcm decode cycles (will speed up ADPCM a little bit). Following diff against aosdk 1.4.1 shows my assumption.

Code
diff -Nru aosdk_base/eng_dsf/aica.c aosdk/eng_dsf/aica.c
--- aosdk_base/eng_dsf/aica.c	2008-03-07 21:21:32.000000000 +0300
+++ aosdk/eng_dsf/aica.c	2008-07-27 23:05:18.596041500 +0400
@@ -125,12 +125,10 @@
 	struct _LFO ALFO;		//Amplitude LFO
 	int slot;
 	int cur_sample;       //current ADPCM sample
-	int nxt_sample;       //next ADPCM sample
 	int cur_quant;        //current ADPCM step
-	int nxt_quant;        //next ADPCM step
-	int curstep, nxtstep;
+	int curstep;
 	int cur_lpquant, cur_lpsample, cur_lpstep;
-	UINT8 *adbase, *nxtbase, *adlpbase;
+	UINT8 *adbase, *adlpbase;
 	UINT8 mslc;			// monitored?
 };
 
@@ -431,10 +429,9 @@
 		UINT8 *base;
 		UINT32 curstep, steps_to_go;
 
-		slot->curstep = slot->nxtstep = 0;
-		slot->adbase = slot->nxtbase = (unsigned char *) (AICA->AICARAM+((SA(slot))&0x7fffff));
+		slot->curstep = 0;
+		slot->adbase = (unsigned char *) (AICA->AICARAM+((SA(slot))&0x7fffff));
 		InitADPCM(&(slot->cur_sample), &(slot->cur_quant));
-		InitADPCM(&(slot->nxt_sample), &(slot->nxt_quant));
 		InitADPCM(&(slot->cur_lpsample), &(slot->cur_lpquant));
 
 		// walk to the ADPCM state at LSA
@@ -956,7 +953,6 @@
 	UINT32 addr1,addr2,addr_select;                                   // current and next sample addresses
 	UINT32 *addr[2]      = {&addr1, &addr2};                          // used for linear interpolation
 	UINT32 *slot_addr[2] = {&(slot->cur_addr), &(slot->nxt_addr)};    //
-	int    *adpcm_sample[2] = {&(slot->cur_sample), &(slot->nxt_sample)};
 
 	if(SSCTL(slot)!=0)	//no FM or noise yet
 		return 0;
@@ -1007,12 +1003,16 @@
 		UINT8 *p1=(unsigned char *) (AICA->AICARAM+((SA(slot)+(addr1>>1))&0x7fffff));
 		UINT8 *p2=(unsigned char *) (AICA->AICARAM+((SA(slot)+(addr2>>1))&0x7fffff));
 		INT32 s;
+		int cur_sample;       //current ADPCM sample
+		int nxt_sample;       //next ADPCM sample
 		INT32 fpart=slot->cur_addr&((1<<SHIFT)-1);
-		UINT32 steps_to_go = addr1, curstep = slot->curstep;
+		UINT32 steps_to_go = addr2, curstep = slot->curstep;
 
 		if (slot->adbase)
 		{
-			// seek to the current sample
+			cur_sample = slot->cur_sample; // may already contains current decoded sample 
+
+			// seek to the interpolation sample
 			while (curstep < steps_to_go)
 			{
 				int shift1, delta1;
@@ -1024,33 +1024,15 @@
 				{
 					base++;
 				}
+				if (curstep == addr1)
+					cur_sample = slot->cur_sample;
 			}
+			nxt_sample = slot->cur_sample;
 
 			slot->adbase = base;
 			slot->curstep = curstep;
 
-			base = slot->nxtbase;
-			curstep = slot->nxtstep;
-			steps_to_go = addr2;
-
-			// seek to the interpolation sample
-			while (curstep < steps_to_go)
-			{
-				int shift1, delta1;
-				shift1 = 4*((curstep&1));
-				delta1 = (*base>>shift1)&0xf;
-				DecodeADPCM(&(slot->nxt_sample),delta1,&(slot->nxt_quant));
-				curstep++;
-				if (!(curstep & 1))
-				{
-					base++;
-				}
-			}
-
-			slot->nxtbase = base;
-			slot->nxtstep = curstep;
-
-			s=(int) slot->cur_sample*((1<<SHIFT)-fpart)+(int) slot->nxt_sample*fpart;
+			s=(int)cur_sample*((1<<SHIFT)-fpart)+(int)nxt_sample*fpart;
 		}
 		else
 		{
@@ -1093,7 +1075,7 @@
 				rem_addr = *slot_addr[addr_select] - (LEA(slot)<<SHIFT);
 				*slot_addr[addr_select]=(LSA(slot)<<SHIFT) + rem_addr;
 
-				if(PCMS(slot)>=2 && addr_select==0)
+				if(PCMS(slot)>=2)
 				{
 					// restore the state @ LSA - the sampler will naturally walk to (LSA + remainder)
 					slot->adbase = &AICA->AICARAM[SA(slot)+(LSA(slot)/2)];
@@ -1106,16 +1088,6 @@
 
 //					printf("Looping: slot_addr %x LSA %x LEA %x step %x base %x\n", *slot_addr[addr_select]>>SHIFT, LSA(slot), LEA(slot), slot->curstep, slot->adbase);
 				}
-				else if(PCMS(slot)>=2 && addr_select==1)
-				{
-					slot->nxtbase = &AICA->AICARAM[SA(slot)+(LSA(slot)/2)];
-					slot->nxtstep = LSA(slot);
-					if (PCMS(slot) == 2)
-					{
-						slot->nxt_sample = slot->cur_lpsample;
-						slot->nxt_quant = slot->cur_lpquant;
-					}
-				}
 			}
 			break;
 		}


Last edited by ajax16384; 07/27/08 07:06 PM.