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authorChad Versace <[email protected]>2013-01-16 19:58:42 -0800
committerChad Versace <[email protected]>2013-01-24 21:24:10 -0800
commit529b6d1f3d80f5651bdb477c20fdbb6f6a4d9746 (patch)
tree206fa5aaa8e51da14b1f5fb87c2ad94ff5e1507a /doxygen/Makefile
parenteac030e38e3cdd4ed4534516e3d3a50c8a372719 (diff)
mesa: Remove rounding bias in _mesa_float_to_half()
Not all float32 values can be exactly represented as a float16. _mesa_float_to_half() rounded such intermediate float32 values to zero by truncating unrepresentable bits in the mantissa. This patch improves _mesa_float_to_half() by rounding intermediate float32 values to the nearest float16; when the float32 is exactly between two float16 values we round to the one with an even mantissa. This behavior is preferred over the old behavior because: - It has reduced bias relative to the old behavior. - 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. Reviewed-by: Ian Romanick <[email protected]> Reviewed-by: Paul Berry <[email protected]> Signed-off-by: Chad Versace <[email protected]>
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