| commit | f7b758899c8a260de81bf9fdfea70cb4d7a9816b | [log] [tgz] |
|---|---|---|
| author | Nicolas Capens <capn@google.com> | Wed Apr 26 09:30:47 2017 -0400 |
| committer | Nicolas Capens <capn@google.com> | Tue May 02 14:02:21 2017 +0000 |
| tree | c4c7af1b7a9a04bea2b06913198cfbad1267b524 | |
| parent | ac6e751fe68241019df1e5da149a7fb9ffc6a05d [diff] |
Emulate rounding to the nearest integer. This implementation works by adding a large value which makes the fractional part no longer fit in the mantissa, and then subtracting it again. It matches nearbyint() for values up to 2^22, positive or negative. The 'magic number' of 0x00C00000 is derived by first observing that the integer values 0x00800000 to 0x00FFFFFF can be represented exactly in single-precision floating-point format but can't have a fractional part because there are 24 mantissa bits (the top one being hidden). So when adding 0x00800000 to for example 0.6, it forces the hardware to round it to the nearest representable integer, being 0x00800001. Subtracting 0x00800000 again gives us 1.0. This works for rounding any value from 0.0 to 0x007FFFFF. However, it doesn't work for negative values, because the intermediate result would be less than 0x00800000 and thus leave some room for fractional bits in the mantissa. The solution is to use 0x00C00000 instead so the range gets split between positive and negative values. Note that values greater than the upper bound will still round to integers, but not the nearest ones, while values less than the lower bound can result in fractional values. Bug b/37495485 Change-Id: I1aed2d831269fcf21b8d3313856a9b9756a532ef Reviewed-on: https://swiftshader-review.googlesource.com/9488 Reviewed-by: Nicolas Capens <capn@google.com> Reviewed-by: Corentin Wallez <cwallez@google.com> Tested-by: Nicolas Capens <capn@google.com>
SwiftShader is a high-performance CPU-based implementation of the OpenGL ES and Direct3D 9 graphics APIs12. Its goal is to provide hardware independence for advanced 3D graphics.
The SwiftShader libraries act as drop-in replacements for graphics drivers.
On Windows, most applications can be made to use SwiftShader's DLLs by placing them in the same folder as the executable. On Linux, the LD_LIBRARY_PATH environment variable or -rpath linker option can be used to direct applications to search for shared libraries in the indicated directory first.
Prebuilt binaries can be found at: https://goo.gl/5MOcdb
See CONTRIBUTING.txt for important contributing requirements.
The canonical repository for SwiftShader is hosted at: https://swiftshader.googlesource.com/SwiftShader
All changes must be reviewed and approved in the Gerrit review tool at: https://swiftshader-review.googlesource.com
Authenticate your account here: https://swiftshader-review.googlesource.com/new-password
All changes require a Change-ID tag in the commit message. A commit hook may be used to add this tag automatically, and can be found at: https://gerrit-review.googlesource.com/tools/hooks/commit-msg. To clone the repository and install the commit hook in one go:
git clone https://swiftshader.googlesource.com/SwiftShader && (cd SwiftShader && curl -Lo `git rev-parse --git-dir`/hooks/commit-msg https://gerrit-review.googlesource.com/tools/hooks/commit-msg ; chmod +x `git rev-parse --git-dir`/hooks/commit-msg)
Changes are uploaded to Gerrit by performing:
git push origin HEAD:refs/for/master
See docs/Index.md.
Public mailing list: swiftshader@googlegroups.com
Bug tracker: https://bugs.chromium.org/p/swiftshader
The SwiftShader project is licensed under the Apache License Version 2.0. You can find a copy of it in LICENSE.txt.
Files in the third_party folder are subject to their respective license.
The legal authors for copyright purposes are listed in AUTHORS.txt.
CONTRIBUTORS.txt contains a list of names of individuals who have contributed to SwiftShader. If you‘re not on the list, but you’ve signed the Google CLA and have contributed more than a formatting change, feel free to request to be added.