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71 lines
2.9 KiB
71 lines
2.9 KiB
# FXdiv
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[](https://github.com/Maratyszcza/FXdiv/blob/master/LICENSE)
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[](https://travis-ci.org/Maratyszcza/FXdiv)
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Header-only library for division via fixed-point multiplication by inverse
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On modern CPUs and GPUs integer division is several times slower than multiplication. FXdiv implements an algorithm to replace an integer division with a multiplication and two shifts. This algorithm improves performance when an application performs repeated divisions by the same divisor.
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## Features
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- Integer division for `uint32_t`, `uint64_t`, and `size_t`
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- Header-only library, no installation or build required
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- Compatible with C99, C++, OpenCL, and CUDA
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- Uses platform-specific compiler intrinsics for optimal performance
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- Covered with unit tests and microbenchmarks
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## Example
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```c
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#include <fxdiv.h>
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/* Division of array by a constant: reference implementation */
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void divide_array_c(size_t length, uint32_t array[], uint32_t divisor) {
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for (size_t i = 0; i < length; i++) {
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array[i] /= divisor;
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}
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}
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/* Division of array by a constant: implementation with FXdiv */
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void divide_array_fxdiv(size_t length, uint32_t array[], uint32_t divisor) {
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const struct fxdiv_divisor_uint32_t precomputed_divisor =
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fxdiv_init_uint32_t(divisor);
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for (size_t i = 0; i < length; i++) {
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array[i] = fxdiv_quotient_uint32_t(array[i], precomputed_divisor);
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}
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}
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```
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## Status
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Currently working features:
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| Platform | uint32_t | uint64_t | size_t |
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| --------------- |:--------:|:--------:|:--------:|
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| x86-64 gcc | Works | Works | Works |
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| x86-64 clang | Works | Works | Works |
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| x86-64 MSVC | Works | Works | Works |
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| x86 gcc | Works | Works | Works |
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| x86 clang | Works | Works | Works |
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| x86 MSVC | Works | Works | Works |
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| ARMv7 gcc | Works | Works | Works |
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| ARMv7 clang | Works | Works | Works |
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| ARMv7 MSVC* | Compiles | Compiles | Compiles |
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| ARM64 gcc | Works | Works | Works |
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| ARM64 clang | Works | Works | Works |
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| ARM64 MSVC* | Compiles | Compiles | Compiles |
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| PPC64 gcc | Works | Works | Works |
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| WAsm clang | Works | Works | Works |
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| Asm.js clang | Works | Works | Works |
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| PNaCl clang | Works | Works | Works |
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| CUDA | Untested | Untested | Untested |
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| OpenCL | Untested | Untested | Untested |
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*ARMv7 and ARM64 builds with MSVC are presumed to work, but were only verified to compile successfully
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## References
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- Granlund, Torbjörn, and Peter L. Montgomery. "Division by invariant integers using multiplication." In ACM SIGPLAN Notices, vol. 29, no. 6, pp. 61-72. ACM, 1994. Available: [gmplib.org/~tege/divcnst-pldi94.pdf](https://gmplib.org/~tege/divcnst-pldi94.pdf)
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