diff --git a/src/util/double.h b/src/util/double.h index b5f604b149b..a6b8ac88f90 100644 --- a/src/util/double.h +++ b/src/util/double.h @@ -25,7 +25,6 @@ #ifndef _DOUBLE_H_ #define _DOUBLE_H_ -#include "half_float.h" #include "u_math.h" #ifdef __cplusplus @@ -48,68 +47,6 @@ _mesa_double_to_float_rtne(double val) return _mesa_double_to_float(val); } -/* - * We round down from double to half float by going through float in between, - * but this can give us inaccurate results in some cases. - * One such case is 0x40ee6a0000000001, which should round to 0x7b9b, but - * going through float first turns into 0x7b9a instead. This is because the - * first non-fitting bit is set, so we get a tie, but with the least - * significant bit of the original number set, the tie should break rounding - * up. - * The cast to float, however, turns into 0x47735000, which when going to half - * still ties, but now we lost the tie-up bit, and instead we round to the - * nearest even, which in this case is down. - * - * To fix this, we check if the original would have tied, and if the tie would - * have rounded up, and if both are true, set the least significant bit of the - * intermediate float to 1, so that a tie on the next cast rounds up as well. - * If the rounding already got rid of the tie, that set bit will just be - * truncated anyway and the end result doesn't change. - * - * Another failing case is 0x40effdffffffffff. This one doesn't have the tie - * from double to half, so it just rounds down to 0x7bff (65504.0), but going - * through float first, it turns into 0x477ff000, which does have the tie bit - * for half set, and when that one gets rounded it turns into 0x7c00 - * (Infinity). - * The fix for that one is to make sure the intermediate float does not have - * the tie bit set if the original didn't have it. - */ -static inline uint16_t -_mesa_double_to_float16_rtne(double val) -{ - int significand_bits16 = 10; - int significand_bits32 = 23; - int significand_bits64 = 52; - int f64_to_16_tie_bit = significand_bits64 - significand_bits16 - 1; - int f32_to_16_tie_bit = significand_bits32 - significand_bits16 - 1; - uint64_t f64_rounds_up_mask = ((1ULL << f64_to_16_tie_bit) - 1); - - union di src; - union fi dst; - - src.d = val; - dst.f = val; - - bool f64_has_tie = (src.ui & (1ULL << f64_to_16_tie_bit)) != 0; - bool f64_rounds_up = (src.ui & f64_rounds_up_mask) != 0; - - dst.ui |= (f64_has_tie && f64_rounds_up); - if (!f64_has_tie) - dst.ui &= ~(1U << f32_to_16_tie_bit); - - return _mesa_float_to_float16_rtne(dst.f); -} - -/* - * double -> float -> half with RTZ doesn't have as many complications as - * RTNE, but we do need to ensure that the double -> float cast also uses RTZ. - */ -static inline uint16_t -_mesa_double_to_float16_rtz(double val) -{ - return _mesa_float_to_float16_rtz(_mesa_double_to_float_rtz(val)); -} - #ifdef __cplusplus } /* extern C */ #endif diff --git a/src/util/half_float.h b/src/util/half_float.h index c7234212e71..cfc35e6ea29 100644 --- a/src/util/half_float.h +++ b/src/util/half_float.h @@ -31,6 +31,7 @@ #include #include "util/detect_arch.h" #include "util/detect_cc.h" +#include "util/double.h" #include "util/u_cpu_detect.h" #if DETECT_ARCH_X86_64 @@ -144,6 +145,67 @@ _mesa_float_is_half(double val) return val == (double) _mesa_half_to_float(fp16_val) && !is_denorm; } +/* + * We round down from double to half float by going through float in between, + * but this can give us inaccurate results in some cases. + * One such case is 0x40ee6a0000000001, which should round to 0x7b9b, but + * going through float first turns into 0x7b9a instead. This is because the + * first non-fitting bit is set, so we get a tie, but with the least + * significant bit of the original number set, the tie should break rounding + * up. + * The cast to float, however, turns into 0x47735000, which when going to half + * still ties, but now we lost the tie-up bit, and instead we round to the + * nearest even, which in this case is down. + * + * To fix this, we check if the original would have tied, and if the tie would + * have rounded up, and if both are true, set the least significant bit of the + * intermediate float to 1, so that a tie on the next cast rounds up as well. + * If the rounding already got rid of the tie, that set bit will just be + * truncated anyway and the end result doesn't change. + * + * Another failing case is 0x40effdffffffffff. This one doesn't have the tie + * from double to half, so it just rounds down to 0x7bff (65504.0), but going + * through float first, it turns into 0x477ff000, which does have the tie bit + * for half set, and when that one gets rounded it turns into 0x7c00 + * (Infinity). + * The fix for that one is to make sure the intermediate float does not have + * the tie bit set if the original didn't have it. + */ +static inline uint16_t +_mesa_double_to_float16_rtne(double val) +{ + int significand_bits16 = 10; + int significand_bits32 = 23; + int significand_bits64 = 52; + int f64_to_16_tie_bit = significand_bits64 - significand_bits16 - 1; + int f32_to_16_tie_bit = significand_bits32 - significand_bits16 - 1; + uint64_t f64_rounds_up_mask = ((1ULL << f64_to_16_tie_bit) - 1); + + union di src; + union fi dst; + + src.d = val; + dst.f = val; + + bool f64_has_tie = (src.ui & (1ULL << f64_to_16_tie_bit)) != 0; + bool f64_rounds_up = (src.ui & f64_rounds_up_mask) != 0; + + dst.ui |= (f64_has_tie && f64_rounds_up); + if (!f64_has_tie) + dst.ui &= ~(1U << f32_to_16_tie_bit); + + return _mesa_float_to_float16_rtne(dst.f); +} + +/* + * double -> float -> half with RTZ doesn't have as many complications as + * RTNE, but we do need to ensure that the double -> float cast also uses RTZ. + */ +static inline uint16_t +_mesa_double_to_float16_rtz(double val) +{ + return _mesa_float_to_float16_rtz(_mesa_double_to_float_rtz(val)); +} #ifdef __cplusplus @@ -154,8 +216,8 @@ namespace mesa struct float16_t { uint16_t bits; - float16_t(float f) : bits(_mesa_float_to_half(f)) {} - float16_t(double d) : bits(_mesa_float_to_half((float)d)) {} + float16_t(float f) : bits(_mesa_float_to_float16_rtne(f)) {} + float16_t(double d) : bits(_mesa_double_to_float16_rtne(d)) {} float16_t(uint16_t raw_bits) : bits(raw_bits) {} static float16_t one() { return float16_t(FP16_ONE); } static float16_t zero() { return float16_t(FP16_ZERO); }