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e9ffd12827
This addresses several issues of the current atan2 implementation:
- Negative zero (and negative denorms which end up getting flushed to
zero) isn't handled correctly by the current implementation. The
reason is that it does 'y >= 0' and 'x < 0' comparisons to decide
on which side of the branch cut the argument is, which causes us to
return incorrect results (off by up to 2π) for very small negative
values.
- There is a serious precision problem for x values of large enough
magnitude introduced by the floating point division operation being
implemented as a mul+rcp sequence. This can lead to the quotient
getting flushed to zero in some cases introducing an error of over
8e6 ULP in the result -- Or in the most catastrophic case will
cause us to return NaN instead of the correct value ±π/2 for y=±∞
and x very large. We can fix this easily by scaling down both
arguments when the absolute value of the denominator goes above
certain threshold. The error of this atan2 implementation remains
below 25 ULP in most of its domain except for a neighborhood of y=0
where it reaches a maximum error of about 180 ULP.
- It emits a bunch of instructions including no less than three
if-else branches per scalar component that don't seem to get
optimized out later on. This implementation uses about 13% less
instructions on Intel SKL hardware and doesn't emit any control
flow instructions.
v2: Fix up argument scaling to take into account the range and
precision of exotic FP24 hardware. Flip coordinate system for
arguments along the vertical line as if they were on the left
half-plane in order to avoid division by zero which may give
unspecified results on non-GLSL 4.1-capable hardware. Sprinkle in
some more comments.
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
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File: docs/README.WIN32 Last updated: 21 June 2013 Quick Start ----- ----- Windows drivers are build with SCons. Makefiles or Visual Studio projects are no longer shipped or supported. Run scons libgl-gdi to build gallium based GDI driver. This will work both with MSVS or Mingw. Windows Drivers ------- ------- At this time, only the gallium GDI driver is known to work. Source code also exists in the tree for other drivers in src/mesa/drivers/windows, but the status of this code is unknown. Recipe ------ Building on windows requires several open-source packages. These are steps that work as of this writing. - install python 2.7 - install scons (latest) - install mingw, flex, and bison - install pywin32 from here: http://www.lfd.uci.edu/~gohlke/pythonlibs get pywin32-218.4.win-amd64-py2.7.exe - install git - download mesa from git see http://www.mesa3d.org/repository.html - run scons General ------- After building, you can copy the above DLL files to a place in your PATH such as $SystemRoot/SYSTEM32. If you don't like putting things in a system directory, place them in the same directory as the executable(s). Be careful about accidentially overwriting files of the same name in the SYSTEM32 directory. The DLL files are built so that the external entry points use the stdcall calling convention. Static LIB files are not built. The LIB files that are built with are the linker import files associated with the DLL files. The si-glu sources are used to build the GLU libs. This was done mainly to get the better tessellator code. If you have a Windows-related build problem or question, please post to the mesa-dev or mesa-users list.