ref: edffe56b309bb5e50338adbe40d29476d2f19d80
parent: fba923d83a843af1c97f78145d57b6430706f4dd
author: Jean-Marc Valin <jeanmarcv@google.com>
date: Fri Mar 21 12:22:09 EDT 2025
Add PSHR32_ovflw() and use it in IMDCT Prevents integer overflow UB in the shift rounding when the signal blows up on bad bitstreams (if it triggers, the signal was already unusable anyway).
--- a/celt/arch.h
+++ b/celt/arch.h
@@ -330,6 +330,8 @@
#define SUB32(a,b) ((a)-(b))
#define ADD32_ovflw(a,b) ((a)+(b))
#define SUB32_ovflw(a,b) ((a)-(b))
+#define PSHR32_ovflw(a,shift) (a)
+
#define MULT16_16_16(a,b) ((a)*(b))
#define MULT16_16(a,b) ((opus_val32)(a)*(opus_val32)(b))
#define MAC16_16(c,a,b) ((c)+(opus_val32)(a)*(opus_val32)(b))
--- a/celt/fixed_debug.h
+++ b/celt/fixed_debug.h
@@ -69,6 +69,8 @@
/* Avoid MSVC warning C4146: unary minus operator applied to unsigned type */
/** Negate 32-bit value, ignore any overflows */
#define NEG32_ovflw(a) (celt_mips+=2,(opus_val32)(0-(opus_uint32)(a)))
+/** 32-bit arithmetic shift right with rounding-to-nearest, ignoring overflows */
+#define PSHR32_ovflw(a,shift) (SHR32(ADD32_ovflw(a, (EXTEND32(1)<<(shift)>>1)),shift))
static OPUS_INLINE short NEG16(int x)
{--- a/celt/fixed_generic.h
+++ b/celt/fixed_generic.h
@@ -147,6 +147,8 @@
/* Avoid MSVC warning C4146: unary minus operator applied to unsigned type */
/** Negate 32-bit value, ignore any overflows */
#define NEG32_ovflw(a) ((opus_val32)(0-(opus_uint32)(a)))
+/** 32-bit arithmetic shift right with rounding-to-nearest, ignoring overflows */
+#define PSHR32_ovflw(a,shift) (SHR32(ADD32_ovflw(a, (EXTEND32(1)<<(shift)>>1)),shift))
/** 16x16 multiplication where the result fits in 16 bits */
#define MULT16_16_16(a,b) ((((opus_val16)(a))*((opus_val16)(b))))
--- a/celt/mdct.c
+++ b/celt/mdct.c
@@ -330,8 +330,8 @@
t0 = t[i];
t1 = t[N4+i];
/* We'd scale up by 2 here, but instead it's done when mixing the windows */
- yr = PSHR32(ADD32_ovflw(S_MUL(re,t0), S_MUL(im,t1)), IMDCT_HEADROOM);
- yi = PSHR32(SUB32_ovflw(S_MUL(re,t1), S_MUL(im,t0)), IMDCT_HEADROOM);
+ yr = PSHR32_ovflw(ADD32_ovflw(S_MUL(re,t0), S_MUL(im,t1)), IMDCT_HEADROOM);
+ yi = PSHR32_ovflw(SUB32_ovflw(S_MUL(re,t1), S_MUL(im,t0)), IMDCT_HEADROOM);
/* We swap real and imag because we're using an FFT instead of an IFFT. */
re = yp1[1];
im = yp1[0];
@@ -341,8 +341,8 @@
t0 = t[(N4-i-1)];
t1 = t[(N2-i-1)];
/* We'd scale up by 2 here, but instead it's done when mixing the windows */
- yr = PSHR32(ADD32_ovflw(S_MUL(re,t0), S_MUL(im,t1)), IMDCT_HEADROOM);
- yi = PSHR32(SUB32_ovflw(S_MUL(re,t1), S_MUL(im,t0)), IMDCT_HEADROOM);
+ yr = PSHR32_ovflw(ADD32_ovflw(S_MUL(re,t0), S_MUL(im,t1)), IMDCT_HEADROOM);
+ yi = PSHR32_ovflw(SUB32_ovflw(S_MUL(re,t1), S_MUL(im,t0)), IMDCT_HEADROOM);
yp1[0] = yr;
yp0[1] = yi;
yp0 += 2;
--
⑨