From 8ea01eed109b3621f3b9e0186ac017119509a5dc Mon Sep 17 00:00:00 2001
From: Jean-Marc Valin <jmvalin@jmvalin.ca>
Date: Wed, 13 Nov 2013 09:39:05 -0500
Subject: [PATCH] Making the CELT fixed-point decoder a bit more robust to
extreme signals
denormalise_bands() can now produce signals close to the max MDCT amplitude.
---
celt/bands.c | 22 +++++++++++++++++++---
1 file changed, 19 insertions(+), 3 deletions(-)
diff --git a/celt/bands.c b/celt/bands.c
index f22951b5c..cce56e2f6 100644
--- a/celt/bands.c
+++ b/celt/bands.c
@@ -214,7 +214,9 @@ void denormalise_bands(const CELTMode *m, const celt_norm * OPUS_RESTRICT X,
j=M*eBands[i];
band_end = M*eBands[i+1];
lg = ADD16(bandLogE[i+c*m->nbEBands], SHL16((opus_val16)eMeans[i],6));
-#ifdef FIXED_POINT
+#ifndef FIXED_POINT
+ g = celt_exp2(lg);
+#else
/* Handle the integer part of the log energy */
shift = 16-(lg>>DB_SHIFT);
if (shift>31)
@@ -225,9 +227,23 @@ void denormalise_bands(const CELTMode *m, const celt_norm * OPUS_RESTRICT X,
/* Handle the fractional part. */
g = celt_exp2_frac(lg&((1<<DB_SHIFT)-1));
}
-#else
- g = celt_exp2(lg);
+ /* Handle extreme gains with negative shift. */
+ if (shift<0)
+ {
+ /* For shift < -2 we'd be likely to overflow, so we're capping
+ the gain here. This shouldn't happen unless the bitstream is
+ already corrupted. */
+ if (shift < -2)
+ {
+ g = 32767;
+ shift = -2;
+ }
+ do {
+ *f++ = SHL32(MULT16_16(*x++, g), -shift);
+ } while (++j<band_end);
+ } else
#endif
+ /* Be careful of the fixed-point "else" just above when changing this code */
do {
*f++ = SHR32(MULT16_16(*x++, g), shift);
} while (++j<band_end);
--
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