[Scummvm-cvs-logs] SF.net SVN: scummvm: [28986] scummvm/branches/gsoc2007-mixer/sound/rate.cpp

[dogmatixman at users.sourceforge.net]

Revision: 28986
          http://scummvm.svn.sourceforge.net/scummvm/?rev=28986&view=rev
Author:   dogmatixman
Date:     2007-09-20 05:59:31 -0700 (Thu, 20 Sep 2007)

Log Message:
-----------
Eliminated circular indexing of the input buffer during the FilteringRateConverter's main filter loop.  This has a tradeoff of doubling the input buffer length.

Modified Paths:
--------------
    scummvm/branches/gsoc2007-mixer/sound/rate.cpp

Modified: scummvm/branches/gsoc2007-mixer/sound/rate.cpp
===================================================================
--- scummvm/branches/gsoc2007-mixer/sound/rate.cpp	2007-09-20 12:47:04 UTC (rev 28985)
+++ scummvm/branches/gsoc2007-mixer/sound/rate.cpp	2007-09-20 12:59:31 UTC (rev 28986)
@@ -411,7 +411,12 @@
 	
 	numChan = (stereo ? 2 : 1);
 	
-	inBuf = (st_sample_t *)calloc(numChan * subLen, sizeof(st_sample_t));
+	/*
+	 * Buffer for the input samples.  Twice the required length is
+	 * allocated so that the input samples can be read linearly in the main
+	 * filtering loop.
+	 */
+	inBuf = (st_sample_t *)calloc(2 * numChan * subLen, sizeof(st_sample_t));
 	
 	inPos = 0;
 	
@@ -438,6 +443,17 @@
 			uint8 inLen;
 			
 			inLen = input.readBuffer(&inBuf[inPos], numChan);
+			
+			/*
+			 * Store a second copy of the input sample(s) so that
+			 * the input buffer can be accessed linearly (rather
+			 * than circularly) during the filtering loop
+			 */
+			inBuf[inPos + numChan * subLen] = inBuf[inPos];
+			if (stereo) {
+				inBuf[inPos + numChan * subLen + 1] = inBuf[inPos + 1];
+			}
+			
 			if (inLen == 0) {
 				/* No more input samples */
 				return this->drain(obuf, (oend - obuf) / 2, vol_l, vol_r);
@@ -459,10 +475,10 @@
 		double *base = coeffs + (currBank * subLen);
 		 
 		for (i = 0; i < subLen; i++) {
-			accum0 += (double)inBuf[(inPos + numChan * i) % (numChan * subLen)]
+			accum0 += (double)inBuf[inPos + numChan * i]
 						* base[i];
 			if (stereo) {
-				accum1 += (double)inBuf[(inPos + numChan * i + 1) % (numChan * subLen)]
+				accum1 += (double)inBuf[inPos + numChan * i + 1]
 						* base[i];
 			}
 		}


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