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util/format: Handle denorms when converting to R11G11B10F

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The spec allows denormals and the R11G11B20F decoder handles them but
the encoder always flushes them to zero.  We should be consistent and
handle denorms going both directions.

Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/28793>
This commit is contained in:
Faith Ekstrand 2024-04-17 17:46:52 -05:00 • committed by Marge Bot
parent ef5e441274
commit cd8a3ea04b
1 changed files with 28 additions and 2 deletions
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30
src/util/format_r11g11b10f.h
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@ -91,7 +91,7 @@ static inline uint32_t f32_to_uf11(float val)
* converted to 65024."
*/
uf11 = UF11(30, 63);
} else if (exponent > -15) { /* Representable value */
} else if (exponent > -15) { /* Normal value */
/* Dividing by 2^exponent gives us a number in the range [1, 2).
* Multiplying by 2^6=64 gives us our mantissa, plus an extra 1 which
* we'll mask off.
@ -109,6 +109,19 @@ static inline uint32_t f32_to_uf11(float val)
mantissa &= UF11_MANTISSA_BITS;
exponent += UF11_EXPONENT_BIAS;
uf11 = UF11(exponent, mantissa);
} else { /* Zero or denormal */
/* Since exponent <= -15, Multiplying by 2^14 gives us a number in the
* range [0, 1). Multiplying by 2^6=64 gives us our mantissa.
*/
mantissa = _mesa_lroundevenf(ldexp(val, 6 + 14));
/* It's possible that we get a normal after rounding */
if ((mantissa >> UF11_EXPONENT_SHIFT) != 0) {
assert(mantissa == (1 << UF11_EXPONENT_SHIFT));
uf11 = UF11(1, 0);
} else {
uf11 = UF11(0, mantissa);
}
}
return uf11;
@ -187,7 +200,7 @@ static inline uint32_t f32_to_uf10(float val)
* converted to 64512."
*/
uf10 = UF10(30, 31);
} else if (exponent > -15) { /* Representable value */
} else if (exponent > -15) { /* Normal value */
/* Dividing by 2^exponent gives us a number in the range [1, 2).
* Multiplying by 2^5=32 gives us our mantissa, plus an extra 1 which
* we'll mask off.
@ -205,6 +218,19 @@ static inline uint32_t f32_to_uf10(float val)
mantissa &= UF10_MANTISSA_BITS;
exponent += UF10_EXPONENT_BIAS;
uf10 = UF10(exponent, mantissa);
} else { /* Zero or denormal */
/* Since exponent <= -15, Multiplying by 2^14 gives us a number in the
* range [0, 1). Multiplying by 2^5=32 gives us our mantissa.
*/
mantissa = _mesa_lroundevenf(ldexp(val, 5 + 14));
/* It's possible that we get a normal after rounding */
if ((mantissa >> UF10_EXPONENT_SHIFT) != 0) {
assert(mantissa == (1 << UF10_EXPONENT_SHIFT));
uf10 = UF10(1, 0);
} else {
uf10 = UF10(0, mantissa);
}
}
return uf10;