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Rescaler: fix rounding error

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We saturate the result to [0..255]
It's the easiest and safest, given the wide variety of scaling
range we cover: we're not using floats, so precision is always
an issue at one end or the other of the scaling spectrum.

we also use:
  round(a - floor(b))
instead of:
  floor(a - round(b))
to handle difficult cases (ratio ~= .99, e.g.)

MIPS code is still disabled (and wrong)

Change-Id: I18d3f5ddc4c524879c257b928329b1c648fa7fb5
This commit is contained in:
Pascal Massimino
2019-03-28 19:44:39 +01:00
parent aa65f89a8f
commit ab2dc8939f
5 changed files with 43 additions and 97 deletions
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32
src/dsp/rescaler_neon.c
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@ -81,14 +81,13 @@ static void RescalerExportRowExpand_NEON(WebPRescaler* const wrk) {
const uint32x4_t B1 = MULT_FIX(A1, fy_scale_half);
const uint16x4_t C0 = vmovn_u32(B0);
const uint16x4_t C1 = vmovn_u32(B1);
const uint8x8_t D = vmovn_u16(vcombine_u16(C0, C1));
const uint8x8_t D = vqmovn_u16(vcombine_u16(C0, C1));
vst1_u8(dst + x_out, D);
}
for (; x_out < x_out_max; ++x_out) {
const uint32_t J = frow[x_out];
const int v = (int)MULT_FIX_C(J, fy_scale);
assert(v >= 0 && v <= 255);
dst[x_out] = v;
dst[x_out] = (v > 255) ? 255u : (uint8_t)v;
}
} else {
const uint32_t B = WEBP_RESCALER_FRAC(-wrk->y_accum, wrk->y_sub);
@ -102,7 +101,7 @@ static void RescalerExportRowExpand_NEON(WebPRescaler* const wrk) {
const uint32x4_t D1 = MULT_FIX(C1, fy_scale_half);
const uint16x4_t E0 = vmovn_u32(D0);
const uint16x4_t E1 = vmovn_u32(D1);
const uint8x8_t F = vmovn_u16(vcombine_u16(E0, E1));
const uint8x8_t F = vqmovn_u16(vcombine_u16(E0, E1));
vst1_u8(dst + x_out, F);
}
for (; x_out < x_out_max; ++x_out) {
@ -110,8 +109,7 @@ static void RescalerExportRowExpand_NEON(WebPRescaler* const wrk) {
+ (uint64_t)B * irow[x_out];
const uint32_t J = (uint32_t)((I + ROUNDER) >> WEBP_RESCALER_RFIX);
const int v = (int)MULT_FIX_C(J, fy_scale);
assert(v >= 0 && v <= 255);
dst[x_out] = v;
dst[x_out] = (v > 255) ? 255u : (uint8_t)v;
}
}
}
@ -135,23 +133,22 @@ static void RescalerExportRowShrink_NEON(WebPRescaler* const wrk) {
for (x_out = 0; x_out < max_span; x_out += 8) {
LOAD_32x8(frow + x_out, in0, in1);
LOAD_32x8(irow + x_out, in2, in3);
const uint32x4_t A0 = MULT_FIX(in0, yscale_half);
const uint32x4_t A1 = MULT_FIX(in1, yscale_half);
const uint32x4_t A0 = MULT_FIX_FLOOR(in0, yscale_half);
const uint32x4_t A1 = MULT_FIX_FLOOR(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_FLOOR(B0, fxy_scale_half);
const uint32x4_t C1 = MULT_FIX_FLOOR(B1, fxy_scale_half);
const uint32x4_t C0 = MULT_FIX(B0, fxy_scale_half);
const uint32x4_t C1 = MULT_FIX(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));
const uint8x8_t E = vqmovn_u16(vcombine_u16(D0, D1));
vst1_u8(dst + x_out, E);
STORE_32x8(A0, A1, irow + x_out);
}
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_FLOOR_C(irow[x_out] - frac, fxy_scale);
assert(v >= 0 && v <= 255);
dst[x_out] = v;
const uint32_t frac = (uint32_t)MULT_FIX_FLOOR_C(frow[x_out], yscale);
const int v = (int)MULT_FIX_C(irow[x_out] - frac, fxy_scale);
dst[x_out] = (v > 255) ? 255u : (uint8_t)v;
irow[x_out] = frac; // new fractional start
}
} else {
@ -161,14 +158,13 @@ static void RescalerExportRowShrink_NEON(WebPRescaler* const wrk) {
const uint32x4_t A1 = MULT_FIX(in1, fxy_scale_half);
const uint16x4_t B0 = vmovn_u32(A0);
const uint16x4_t B1 = vmovn_u32(A1);
const uint8x8_t C = vmovn_u16(vcombine_u16(B0, B1));
const uint8x8_t C = vqmovn_u16(vcombine_u16(B0, B1));
vst1_u8(dst + x_out, C);
STORE_32x8(zero, zero, irow + x_out);
}
for (; x_out < x_out_max; ++x_out) {
const int v = (int)MULT_FIX_C(irow[x_out], fxy_scale);
assert(v >= 0 && v <= 255);
dst[x_out] = v;
dst[x_out] = (v > 255) ? 255u : (uint8_t)v;
irow[x_out] = 0;
}
}