From cbceaa8579e16c0690e6f6469c459d889b0a3e36 Mon Sep 17 00:00:00 2001
From: Jean-Marc Valin <jmvalin@jmvalin.ca>
Date: Sun, 24 Jul 2016 15:30:40 -0400
Subject: [PATCH] Directly saturate the comb filter output
Otherwise, the output can grow as large as SIG_SAT/(1-0.75), which can cause
an overflow when adding two values (before multiplying by the filter tap).
---
celt/celt.c | 17 ++++++++---------
1 file changed, 8 insertions(+), 9 deletions(-)
diff --git a/celt/celt.c b/celt/celt.c
index 8502fdb98..f332191c6 100644
--- a/celt/celt.c
+++ b/celt/celt.c
@@ -111,26 +111,31 @@ void comb_filter_const_c(opus_val32 *y, opus_val32 *x, int T, int N,
t = MAC16_32_Q16(x[i], g10, x2);
t = MAC16_32_Q16(t, g11, ADD32(x1,x3));
t = MAC16_32_Q16(t, g12, ADD32(x0,x4));
+ t = SATURATE(t, SIG_SAT);
y[i] = t;
x4=SHL32(x[i-T+3],1);
t = MAC16_32_Q16(x[i+1], g10, x1);
t = MAC16_32_Q16(t, g11, ADD32(x0,x2));
t = MAC16_32_Q16(t, g12, ADD32(x4,x3));
+ t = SATURATE(t, SIG_SAT);
y[i+1] = t;
x3=SHL32(x[i-T+4],1);
t = MAC16_32_Q16(x[i+2], g10, x0);
t = MAC16_32_Q16(t, g11, ADD32(x4,x1));
t = MAC16_32_Q16(t, g12, ADD32(x3,x2));
+ t = SATURATE(t, SIG_SAT);
y[i+2] = t;
x2=SHL32(x[i-T+5],1);
t = MAC16_32_Q16(x[i+3], g10, x4);
t = MAC16_32_Q16(t, g11, ADD32(x3,x0));
t = MAC16_32_Q16(t, g12, ADD32(x2,x1));
+ t = SATURATE(t, SIG_SAT);
y[i+3] = t;
x1=SHL32(x[i-T+6],1);
t = MAC16_32_Q16(x[i+4], g10, x3);
t = MAC16_32_Q16(t, g11, ADD32(x2,x4));
t = MAC16_32_Q16(t, g12, ADD32(x1,x0));
+ t = SATURATE(t, SIG_SAT);
y[i+4] = t;
}
#ifdef CUSTOM_MODES
@@ -141,6 +146,7 @@ void comb_filter_const_c(opus_val32 *y, opus_val32 *x, int T, int N,
t = MAC16_32_Q16(x[i], g10, x2);
t = MAC16_32_Q16(t, g11, ADD32(x1,x3));
t = MAC16_32_Q16(t, g12, ADD32(x0,x4));
+ t = SATURATE(t, SIG_SAT);
y[i] = t;
x4=x3;
x3=x2;
@@ -169,6 +175,7 @@ void comb_filter_const_c(opus_val32 *y, opus_val32 *x, int T, int N,
+ MULT16_32_Q15(g10,x2)
+ MULT16_32_Q15(g11,ADD32(x1,x3))
+ MULT16_32_Q15(g12,ADD32(x0,x4));
+ y[i] = SATURATE(y[i], SIG_SAT);
x4=x3;
x3=x2;
x2=x1;
@@ -225,6 +232,7 @@ void comb_filter(opus_val32 *y, opus_val32 *x, int T0, int T1, int N,
+ MULT16_32_Q15(MULT16_16_Q15(f,g10),x2)
+ MULT16_32_Q15(MULT16_16_Q15(f,g11),ADD32(x1,x3))
+ MULT16_32_Q15(MULT16_16_Q15(f,g12),ADD32(x0,x4));
+ y[i] = SATURATE(y[i], SIG_SAT);
x4=x3;
x3=x2;
x2=x1;
@@ -236,20 +244,11 @@ void comb_filter(opus_val32 *y, opus_val32 *x, int T0, int T1, int N,
/* OPT: Happens to work without the OPUS_MOVE(), but only because the current encoder already copies x to y */
if (x!=y)
OPUS_MOVE(y+overlap, x+overlap, N-overlap);
-#ifdef FIXED_POINT
- for (i=0; i < overlap; i++)
- y[i] = SATURATE(y[i], SIG_SAT);
-#endif
return;
}
/* Compute the part with the constant filter. */
comb_filter_const(y+i, x+i, T1, N-i, g10, g11, g12, arch);
-#ifdef FIXED_POINT
- for (i=0; i < N; i++)
- y[i] = SATURATE(y[i], SIG_SAT);
-#endif
-
}
#endif /* OVERRIDE_comb_filter */
--
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