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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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18
src/dsp/rescaler_neon.c
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@ -22,6 +22,7 @@
#define ROUNDER (WEBP_RESCALER_ONE >> 1)
#define MULT_FIX_C(x, y) (((uint64_t)(x) * (y) + ROUNDER) >> WEBP_RESCALER_RFIX)
#define MULT_FIX_FLOOR_C(x, y) (((uint64_t)(x) * (y)) >> WEBP_RESCALER_RFIX)
#define LOAD_32x4(SRC, DST) const uint32x4_t DST = vld1q_u32((SRC))
#define LOAD_32x8(SRC, DST0, DST1) \
@ -35,8 +36,11 @@
#if (WEBP_RESCALER_RFIX == 32)
#define MAKE_HALF_CST(C) vdupq_n_s32((int32_t)((C) >> 1))
#define MULT_FIX(A, B) /* note: B is actualy scale>>1. See MAKE_HALF_CST */ \
// note: B is actualy scale>>1. See MAKE_HALF_CST
#define MULT_FIX(A, B) \
vreinterpretq_u32_s32(vqrdmulhq_s32(vreinterpretq_s32_u32((A)), (B)))
#define MULT_FIX_FLOOR(A, B) \
vreinterpretq_u32_s32(vqdmulhq_s32(vreinterpretq_s32_u32((A)), (B)))
#else
#error "MULT_FIX/WEBP_RESCALER_RFIX need some more work"
#endif
@ -135,8 +139,8 @@ static void RescalerExportRowShrink_NEON(WebPRescaler* const wrk) {
const uint32x4_t A1 = MULT_FIX(in1, yscale_half);
const uint32x4_t B0 = vqsubq_u32(in2, A0);
const uint32x4_t B1 = vqsubq_u32(in3, A1);
const uint32x4_t C0 = MULT_FIX(B0, fxy_scale_half);
const uint32x4_t C1 = MULT_FIX(B1, fxy_scale_half);
const uint32x4_t C0 = MULT_FIX_FLOOR(B0, fxy_scale_half);
const uint32x4_t C1 = MULT_FIX_FLOOR(B1, fxy_scale_half);
const uint16x4_t D0 = vmovn_u32(C0);
const uint16x4_t D1 = vmovn_u32(C1);
const uint8x8_t E = vmovn_u16(vcombine_u16(D0, D1));
@ -145,7 +149,7 @@ static void RescalerExportRowShrink_NEON(WebPRescaler* const wrk) {
}
for (; x_out < x_out_max; ++x_out) {
const uint32_t frac = (uint32_t)MULT_FIX_C(frow[x_out], yscale);
const int v = (int)MULT_FIX_C(irow[x_out] - frac, wrk->fxy_scale);
const int v = (int)MULT_FIX_FLOOR_C(irow[x_out] - frac, fxy_scale);
assert(v >= 0 && v <= 255);
dst[x_out] = v;
irow[x_out] = frac; // new fractional start
@ -170,6 +174,12 @@ static void RescalerExportRowShrink_NEON(WebPRescaler* const wrk) {
}
}
#undef MULT_FIX_FLOOR_C
#undef MULT_FIX_C
#undef MULT_FIX_FLOOR
#undef MULT_FIX
#undef ROUNDER
//------------------------------------------------------------------------------
extern void WebPRescalerDspInitNEON(void);