https://github.com/maratyszcza/fxdiv

C99/C++ header-only library for division via fixed-point multiplication by inverse
https://github.com/maratyszcza/fxdiv

algorithm division fixed-point integer-division

Last synced: 6 days ago
JSON representation

C99/C++ header-only library for division via fixed-point multiplication by inverse

• Host: GitHub
• URL: https://github.com/maratyszcza/fxdiv
• Owner: Maratyszcza
• License: mit
• Created: 2016-07-02T17:04:24.000Z (over 8 years ago)
• Default Branch: master
• Last Pushed: 2024-04-14T10:13:56.000Z (9 months ago)
• Last Synced: 2024-12-19T20:41:42.079Z (9 days ago)
• Topics: algorithm, division, fixed-point, integer-division
• Language: C++
• Homepage:
• Size: 39.1 KB
• Stars: 49
• Watchers: 9
• Forks: 46
• Open Issues: 3
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

Awesome Lists containing this project

README

        
# FXdiv

[![MIT License](https://img.shields.io/badge/License-MIT%20License-blue.svg)](https://github.com/Maratyszcza/FXdiv/blob/master/LICENSE)

[![Build Status](https://img.shields.io/travis/Maratyszcza/FXdiv.svg)](https://travis-ci.org/Maratyszcza/FXdiv)

Header-only library for division via fixed-point multiplication by inverse

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.

## Features

- Integer division for `uint32_t`, `uint64_t`, and `size_t`

- Header-only library, no installation or build required

- Compatible with C99, C++, OpenCL, and CUDA

- Uses platform-specific compiler intrinsics for optimal performance

- Covered with unit tests and microbenchmarks

## Example

```c

#include 

/* Division of array by a constant: reference implementation */

void divide_array_c(size_t length, uint32_t array[], uint32_t divisor) {

  for (size_t i = 0; i < length; i++) {

    array[i] /= divisor;

  }

}

/* Division of array by a constant: implementation with FXdiv */

void divide_array_fxdiv(size_t length, uint32_t array[], uint32_t divisor) {

  const struct fxdiv_divisor_uint32_t precomputed_divisor =

    fxdiv_init_uint32_t(divisor);

  for (size_t i = 0; i < length; i++) {

    array[i] = fxdiv_quotient_uint32_t(array[i], precomputed_divisor);

  }

}

```

## Status

Currently working features:

| Platform        | uint32_t | uint64_t | size_t   |

| --------------- |:--------:|:--------:|:--------:|

| x86-64 gcc      | Works    | Works    | Works    |

| x86-64 clang    | Works    | Works    | Works    |

| x86-64 MSVC     | Works    | Works    | Works    |

| x86 gcc         | Works    | Works    | Works    |

| x86 clang       | Works    | Works    | Works    |

| x86 MSVC        | Works    | Works    | Works    |

| ARMv7 gcc       | Works    | Works    | Works    |

| ARMv7 clang     | Works    | Works    | Works    |

| ARMv7 MSVC*     | Compiles | Compiles | Compiles |

| ARM64 gcc       | Works    | Works    | Works    |

| ARM64 clang     | Works    | Works    | Works    |

| ARM64 MSVC*     | Compiles | Compiles | Compiles |

| PPC64 gcc       | Works    | Works    | Works    |

| WAsm clang      | Works    | Works    | Works    |

| Asm.js clang    | Works    | Works    | Works    |

| PNaCl clang     | Works    | Works    | Works    |

| CUDA            | Untested | Untested | Untested |

| OpenCL          | Untested | Untested | Untested |

*ARMv7 and ARM64 builds with MSVC are presumed to work, but were only verified to compile successfully

## References

- 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)