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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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16
src/dsp/rescaler_mips_dsp_r2.c
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@ -107,10 +107,9 @@ static void ExportRowShrink_MIPSdspR2(WebPRescaler* const wrk) {
);
}
for (i = 0; i < (x_out_max & 0x3); ++i) {
const uint32_t frac = (uint32_t)MULT_FIX(*frow++, yscale);
const int v = (int)MULT_FIX_FLOOR(*irow - frac, wrk->fxy_scale);
assert(v >= 0 && v <= 255);
*dst++ = v;
const uint32_t frac = (uint32_t)MULT_FIX_FLOOR(*frow++, yscale);
const int v = (int)MULT_FIX(*irow - frac, wrk->fxy_scale);
*dst++ = (v > 255) ? 255u : (uint8_t)v;
*irow++ = frac; // new fractional start
}
} else {
@ -157,8 +156,7 @@ static void ExportRowShrink_MIPSdspR2(WebPRescaler* const wrk) {
}
for (i = 0; i < (x_out_max & 0x3); ++i) {
const int v = (int)MULT_FIX_FLOOR(*irow, wrk->fxy_scale);
assert(v >= 0 && v <= 255);
*dst++ = v;
*dst++ = (v > 255) ? 255u : (uint8_t)v;
*irow++ = 0;
}
}
@ -219,8 +217,7 @@ static void ExportRowExpand_MIPSdspR2(WebPRescaler* const wrk) {
for (i = 0; i < (x_out_max & 0x3); ++i) {
const uint32_t J = *frow++;
const int v = (int)MULT_FIX(J, wrk->fy_scale);
assert(v >= 0 && v <= 255);
*dst++ = v;
*dst++ = (v > 255) ? 255u : (uint8_t)v;
}
} else {
const uint32_t B = WEBP_RESCALER_FRAC(-wrk->y_accum, wrk->y_sub);
@ -291,8 +288,7 @@ static void ExportRowExpand_MIPSdspR2(WebPRescaler* const wrk) {
+ (uint64_t)B * *irow++;
const uint32_t J = (uint32_t)((I + ROUNDER) >> WEBP_RESCALER_RFIX);
const int v = (int)MULT_FIX(J, wrk->fy_scale);
assert(v >= 0 && v <= 255);
*dst++ = v;
*dst++ = (v > 255) ? 255u : (uint8_t)v;
}
}
}