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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_msa.c
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@ -166,8 +166,7 @@ static WEBP_INLINE void ExportRowExpand_0(const uint32_t* frow, uint8_t* dst,
for (x_out = 0; x_out < length; ++x_out) {
const uint32_t J = frow[x_out];
const int v = (int)MULT_FIX(J, wrk->fy_scale);
assert(v >= 0 && v <= 255);
dst[x_out] = v;
dst[x_out] = (v > 255) ? 255u : (uint8_t)v;
}
}
}
@ -241,8 +240,7 @@ static WEBP_INLINE void ExportRowExpand_1(const uint32_t* frow, uint32_t* irow,
+ (uint64_t)B * irow[x_out];
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[x_out] = v;
dst[x_out] = (v > 255) ? 255u : (uint8_t)v;
}
}
}
@ -342,10 +340,9 @@ static WEBP_INLINE void ExportRowShrink_0(const uint32_t* frow, uint32_t* irow,
length -= 4;
}
for (x_out = 0; x_out < length; ++x_out) {
const uint32_t frac = (uint32_t)MULT_FIX(frow[x_out], yscale);
const int v = (int)MULT_FIX_FLOOR(irow[x_out] - frac, wrk->fxy_scale);
assert(v >= 0 && v <= 255);
dst[x_out] = v;
const uint32_t frac = (uint32_t)MULT_FIX_FLOOR(frow[x_out], yscale);
const int v = (int)MULT_FIX(irow[x_out] - frac, wrk->fxy_scale);
dst[x_out] = (v > 255) ? 255u : (uint8_t)v;
irow[x_out] = frac;
}
}
@ -406,8 +403,7 @@ static WEBP_INLINE void ExportRowShrink_1(uint32_t* irow, uint8_t* dst,
}
for (x_out = 0; x_out < length; ++x_out) {
const int v = (int)MULT_FIX(irow[x_out], wrk->fxy_scale);
assert(v >= 0 && v <= 255);
dst[x_out] = v;
dst[x_out] = (v > 255) ? 255u : (uint8_t)v;
irow[x_out] = 0;
}
}