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author | marha <marha@users.sourceforge.net> | 2013-01-28 07:58:44 +0100 |
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committer | marha <marha@users.sourceforge.net> | 2013-01-28 07:58:44 +0100 |
commit | 39b49babc915183f4d712053b46f0e010427c191 (patch) | |
tree | b512cf3f17a0defe9e2cd6ababdc9f5337f93d0e /mesalib/src/mesa/main/imports.c | |
parent | 3e3af07f7697e9d23dd62fcf8f3a055602ae3341 (diff) | |
parent | 69c8cec54b01ed522bf10baf20da70304bac701a (diff) | |
download | vcxsrv-39b49babc915183f4d712053b46f0e010427c191.tar.gz vcxsrv-39b49babc915183f4d712053b46f0e010427c191.tar.bz2 vcxsrv-39b49babc915183f4d712053b46f0e010427c191.zip |
Merge remote-tracking branch 'origin/released'
* origin/released:
mesa mkfontscale pixman git update 28 jan 2013
Diffstat (limited to 'mesalib/src/mesa/main/imports.c')
-rw-r--r-- | mesalib/src/mesa/main/imports.c | 86 |
1 files changed, 57 insertions, 29 deletions
diff --git a/mesalib/src/mesa/main/imports.c b/mesalib/src/mesa/main/imports.c index 76f835e0e..e6f754254 100644 --- a/mesalib/src/mesa/main/imports.c +++ b/mesalib/src/mesa/main/imports.c @@ -314,10 +314,43 @@ _mesa_bitcount_64(uint64_t n) #endif +/* Using C99 rounding functions for roundToEven() implementation is + * difficult, because round(), rint, and nearbyint() are affected by + * fesetenv(), which the application may have done for its own + * purposes. Mesa's IROUND macro is close to what we want, but it + * rounds away from 0 on n + 0.5. + */ +int +_mesa_round_to_even(float val) +{ + int rounded = IROUND(val); + + if (val - floor(val) == 0.5) { + if (rounded % 2 != 0) + rounded += val > 0 ? -1 : 1; + } + + return rounded; +} + + /** * Convert a 4-byte float to a 2-byte half float. - * Based on code from: - * http://www.opengl.org/discussion_boards/ubb/Forum3/HTML/008786.html + * + * Not all float32 values can be represented exactly as a float16 value. We + * round such intermediate float32 values to the nearest float16. When the + * float32 lies exactly between to float16 values, we round to the one with + * an even mantissa. + * + * This rounding behavior has several benefits: + * - It has no sign bias. + * + * - It reproduces the behavior of real hardware: opcode F32TO16 in Intel's + * GPU ISA. + * + * - By reproducing the behavior of the GPU (at least on Intel hardware), + * compile-time evaluation of constant packHalf2x16 GLSL expressions will + * result in the same value as if the expression were executed on the GPU. */ GLhalfARB _mesa_float_to_half(float val) @@ -356,32 +389,13 @@ _mesa_float_to_half(float val) else { /* regular number */ const int new_exp = flt_e - 127; - if (new_exp < -24) { - /* this maps to 0 */ - /* m = 0; - already set */ - e = 0; - } - else if (new_exp < -14) { - /* this maps to a denorm */ - unsigned int exp_val = (unsigned int) (-14 - new_exp); /* 2^-exp_val*/ + if (new_exp < -14) { + /* The float32 lies in the range (0.0, min_normal16) and is rounded + * to a nearby float16 value. The result will be either zero, subnormal, + * or normal. + */ e = 0; - switch (exp_val) { - case 0: - _mesa_warning(NULL, - "float_to_half: logical error in denorm creation!\n"); - /* m = 0; - already set */ - break; - case 1: m = 512 + (flt_m >> 14); break; - case 2: m = 256 + (flt_m >> 15); break; - case 3: m = 128 + (flt_m >> 16); break; - case 4: m = 64 + (flt_m >> 17); break; - case 5: m = 32 + (flt_m >> 18); break; - case 6: m = 16 + (flt_m >> 19); break; - case 7: m = 8 + (flt_m >> 20); break; - case 8: m = 4 + (flt_m >> 21); break; - case 9: m = 2 + (flt_m >> 22); break; - case 10: m = 1; break; - } + m = _mesa_round_to_even((1 << 24) * fabsf(fi.f)); } else if (new_exp > 15) { /* map this value to infinity */ @@ -389,12 +403,26 @@ _mesa_float_to_half(float val) e = 31; } else { - /* regular */ + /* The float32 lies in the range + * [min_normal16, max_normal16 + max_step16) + * and is rounded to a nearby float16 value. The result will be + * either normal or infinite. + */ e = new_exp + 15; - m = flt_m >> 13; + m = _mesa_round_to_even(flt_m / (float) (1 << 13)); } } + assert(0 <= m && m <= 1024); + if (m == 1024) { + /* The float32 was rounded upwards into the range of the next exponent, + * so bump the exponent. This correctly handles the case where f32 + * should be rounded up to float16 infinity. + */ + ++e; + m = 0; + } + result = (s << 15) | (e << 10) | m; return result; } |