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Add PSHR32_ovflw() and use it in IMDCT

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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).
This commit is contained in:
Jean-Marc Valin 2025-03-21 16:22:09 -04:00
parent fba923d83a
commit edffe56b30
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GPG key ID: 8D2952BBB52C646D
4 changed files with 10 additions and 4 deletions
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2
celt/arch.h
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@ -330,6 +330,8 @@ static OPUS_INLINE int celt_isnan(float x)
#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))

2
celt/fixed_debug.h
View file

@ -69,6 +69,8 @@ extern opus_int64 celt_mips;
/* 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)
{

2
celt/fixed_generic.h
View file

@ -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))))

8
celt/mdct.c
View file

@ -330,8 +330,8 @@ void clt_mdct_backward_c(const mdct_lookup *l, kiss_fft_scalar *in, kiss_fft_sca
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 @@ void clt_mdct_backward_c(const mdct_lookup *l, kiss_fft_scalar *in, kiss_fft_sca
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;