ref: 3c60bae2d74b4b9898b5f4925d4a1fb464a3fa43
parent: a0bd7d3b8420be9c96f4e65e6113e11a05a23717
author: Jean-Marc Valin <jmvalin@jmvalin.ca>
date: Fri Jul 22 07:05:19 EDT 2016
Prevent overflows in PLC celt_iir()
--- a/celt/celt_decoder.c
+++ b/celt/celt_decoder.c
@@ -632,7 +632,23 @@
SIG_SHIFT);
S1 += SHR32(MULT16_16(tmp, tmp), 9);
}
-
+#ifdef FIXED_POINT
+ /* For fixed-point, apply bandwidth expansion until we can guarantee that
+ no overflow can happen in the IIR filter. This means:
+ attenuation*32768*sum(abs(filter)) < 2^31 */
+ while (1) {+ opus_val16 tmp=Q15ONE;
+ opus_val32 sum=QCONST16(1., SIG_SHIFT);
+ for (i=0;i<LPC_ORDER;i++)
+ sum += ABS16(lpc[c*LPC_ORDER+i]);
+ if (MULT16_32_Q15(attenuation, sum) < 65535) break;
+ for (i=0;i<LPC_ORDER;i++)
+ {+ tmp = MULT16_16_Q15(QCONST16(.99f,15), tmp);
+ lpc[c*LPC_ORDER+i] = MULT16_16_Q15(lpc[c*LPC_ORDER+i], tmp);
+ }
+ }
+#endif
{opus_val16 lpc_mem[LPC_ORDER];
/* Copy the last decoded samples (prior to the overlap region) to