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fix rescaling rounding inaccuracy

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We should be using 'floor' when doing the final divide.

-> new MACRO is MULT_FIX_FLOOR()

     XXX*** Mips code is DISABLED for now ***XXX

I'll update and re-enable it in a later
patch, since this code needs some refactoring first.

BUG=oss-fuzz:9179

Change-Id: Ic0693cdca4e71f5beab1029475e35c4d06b12d13
This commit is contained in:
Pascal Massimino
2018-07-10 17:27:21 -07:00
committed by James Zern
parent 211f37ee63
commit 2563db4759
6 changed files with 65 additions and 13 deletions
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35
src/dsp/rescaler_sse2.c
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@ -25,6 +25,7 @@
#define ROUNDER (WEBP_RESCALER_ONE >> 1)
#define MULT_FIX(x, y) (((uint64_t)(x) * (y) + ROUNDER) >> WEBP_RESCALER_RFIX)
#define MULT_FIX_FLOOR(x, y) (((uint64_t)(x) * (y)) >> WEBP_RESCALER_RFIX)
// input: 8 bytes ABCDEFGH -> output: A0E0B0F0C0G0D0H0
static void LoadTwoPixels_SSE2(const uint8_t* const src, __m128i* out) {
@ -224,6 +225,35 @@ static WEBP_INLINE void ProcessRow_SSE2(const __m128i* const A0,
_mm_storel_epi64((__m128i*)dst, G);
}
static WEBP_INLINE void ProcessRow_Floor_SSE2(const __m128i* const A0,
const __m128i* const A1,
const __m128i* const A2,
const __m128i* const A3,
const __m128i* const mult,
uint8_t* const dst) {
const __m128i mask = _mm_set_epi32(0xffffffffu, 0, 0xffffffffu, 0);
const __m128i B0 = _mm_mul_epu32(*A0, *mult);
const __m128i B1 = _mm_mul_epu32(*A1, *mult);
const __m128i B2 = _mm_mul_epu32(*A2, *mult);
const __m128i B3 = _mm_mul_epu32(*A3, *mult);
const __m128i D0 = _mm_srli_epi64(B0, WEBP_RESCALER_RFIX);
const __m128i D1 = _mm_srli_epi64(B1, WEBP_RESCALER_RFIX);
#if (WEBP_RESCALER_RFIX < 32)
const __m128i D2 =
_mm_and_si128(_mm_slli_epi64(B2, 32 - WEBP_RESCALER_RFIX), mask);
const __m128i D3 =
_mm_and_si128(_mm_slli_epi64(B3, 32 - WEBP_RESCALER_RFIX), mask);
#else
const __m128i D2 = _mm_and_si128(B2, mask);
const __m128i D3 = _mm_and_si128(B3, mask);
#endif
const __m128i E0 = _mm_or_si128(D0, D2);
const __m128i E1 = _mm_or_si128(D1, D3);
const __m128i F = _mm_packs_epi32(E0, E1);
const __m128i G = _mm_packus_epi16(F, F);
_mm_storel_epi64((__m128i*)dst, G);
}
static void RescalerExportRowExpand_SSE2(WebPRescaler* const wrk) {
int x_out;
uint8_t* const dst = wrk->dst;
@ -322,12 +352,12 @@ static void RescalerExportRowShrink_SSE2(WebPRescaler* const wrk) {
const __m128i G1 = _mm_or_si128(D1, F3);
_mm_storeu_si128((__m128i*)(irow + x_out + 0), G0);
_mm_storeu_si128((__m128i*)(irow + x_out + 4), G1);
ProcessRow_SSE2(&E0, &E1, &E2, &E3, &mult_xy, dst + x_out);
ProcessRow_Floor_SSE2(&E0, &E1, &E2, &E3, &mult_xy, dst + x_out);
}
}
for (; x_out < x_out_max; ++x_out) {
const uint32_t frac = (int)MULT_FIX(frow[x_out], yscale);
const int v = (int)MULT_FIX(irow[x_out] - frac, wrk->fxy_scale);
const int v = (int)MULT_FIX_FLOOR(irow[x_out] - frac, wrk->fxy_scale);
assert(v >= 0 && v <= 255);
dst[x_out] = v;
irow[x_out] = frac; // new fractional start
@ -352,6 +382,7 @@ static void RescalerExportRowShrink_SSE2(WebPRescaler* const wrk) {
}
}
#undef MULT_FIX_FLOOR
#undef MULT_FIX
#undef ROUNDER