[Flake-enc-svnlog] SF.net SVN: flake-enc:[246] libflake

[<jb...@us...>]

Revision: 246
          http://flake-enc.svn.sourceforge.net/flake-enc/?rev=246&view=rev
Author:   jbr79
Date:     2009-05-20 00:44:29 +0000 (Wed, 20 May 2009)

Log Message:
-----------
add support for shifting out wasted low-order bits

Modified Paths:
--------------
    libflake/encode.c
    libflake/encode.h

Modified: libflake/encode.c
===================================================================
--- libflake/encode.c	2009-05-19 23:43:18 UTC (rev 245)
+++ libflake/encode.c	2009-05-20 00:44:29 UTC (rev 246)
@@ -526,6 +526,7 @@
     // initialize output bps for each channel
     for(ch=0; ch<ctx->channels; ch++) {
         frame->subframes[ch].obits = ctx->bps;
+        frame->subframes[ch].wasted_bits = 0;
     }
 
     return 0;
@@ -549,6 +550,46 @@
 }
 
 /**
+ * Shift out any zero bits and set the wasted_bits parameter.
+ */
+static void
+remove_wasted_bits(FlacEncodeContext *ctx)
+{
+    int i, ch, b;
+    int wasted;
+    FlacFrame *frame;
+    int32_t *samples;
+
+    frame = &ctx->frame;
+    for (ch = 0; ch < ctx->channels; ch++) {
+        wasted = ctx->bps-1;
+        samples = frame->subframes[ch].samples;
+        for (i = 0; i < frame->blocksize; i++) {
+            int32_t s = samples[i];
+            uint32_t mask = 0x1;
+            for (b = 0; b <= wasted; b++) {
+                if (s & mask)
+                    break;
+                mask <<= 1;
+            }
+            if (b < wasted)
+                wasted = b;
+            if (!wasted)
+                break;
+        }
+        if (wasted == ctx->bps-1) {
+            wasted = 0;
+        } else if (wasted) {
+            for (i = 0; i < frame->blocksize; i++) {
+                samples[i] >>= wasted;
+            }
+            frame->subframes[ch].obits -= wasted;
+        }
+        frame->subframes[ch].wasted_bits = wasted;
+    }
+}
+
+/**
  * Estimate the best stereo decorrelation mode
  */
 static int
@@ -838,7 +879,13 @@
         // subframe header
         bitwriter_writebits(ctx->bw, 1, 0);
         bitwriter_writebits(ctx->bw, 6, frame->subframes[ch].type_code);
-        bitwriter_writebits(ctx->bw, 1, 0);
+        if (frame->subframes[ch].wasted_bits) {
+            bitwriter_writebits(ctx->bw, 1, 1);
+            bitwriter_writebits(ctx->bw, frame->subframes[ch].wasted_bits-1, 0);
+            bitwriter_writebits(ctx->bw, 1, 1);
+        } else {
+            bitwriter_writebits(ctx->bw, 1, 0);
+        }
 
         // subframe
         switch(frame->subframes[ch].type) {
@@ -883,6 +930,8 @@
 
     channel_decorrelation(ctx);
 
+    remove_wasted_bits(ctx);
+
     for(ch=0; ch<ctx->channels; ch++) {
         if(encode_residual(ctx, ch) < 0) {
             return -1;

Modified: libflake/encode.h
===================================================================
--- libflake/encode.h	2009-05-19 23:43:18 UTC (rev 245)
+++ libflake/encode.h	2009-05-20 00:44:29 UTC (rev 246)
@@ -52,6 +52,7 @@
 typedef struct FlacSubframe {
     int type;
     int type_code;
+    int wasted_bits;
     int order;
     int obits;
     int32_t coefs[MAX_LPC_ORDER];


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