SWF Fixed

SWF fixed-point numbers for Rust.

A fixed point number represents a decimal values using evenly-distributed bit patterns (as opposed to floating point numbers where the density increases with the proximity to zero).

A fixed point number can be simply thought as an integer divided by a constant value. It is described by its integer part and fractional part: its mathematical value is integer_part + fractional_part / 2^fractional_bits.

For example, the type Ufixed8p8 is an unsigned fixed point number with an 8 bit integer part and 8 bit fractional part. It can represent the 2^16 values corresponding to u16 / 256, the gap between each value (epsilon) is 1 / 256.

This crate defines the fixed points numbers used by SWF files:

Name	Integer part	Fractional part	Min value	Max value	Epsilon
Sfixed8P8	i8	u8	-128	128 - 1/256	1 / 256
Ufixed8P8	u8	u8	0	256 - 1/256	1 / 256
Sfixed16P16	i16	u16	-2^15	2^15 - 1/2^16	1 / 2^16
Ufixed16P16	u16	u16	0	2^16 - 1/2^16	1 / 2^16

Usage

use swf_fixed::Sfixed8P8;

fn main() {
  let a = Sfixed8P8::from_epsilons(256);
  let b = Sfixed8P8::from_value(1f32);
  assert_eq!(a, b);
  let sum: Sfixed8P8 = (a + b);
  let sum_value: f32 = sum.into();
  assert_eq!(sum_value, 2.0f32);
}

Contributing

This library is a standard Cargo project. You can test your changes with cargo test.

Prefer non-master branches when sending a PR so your changes can be rebased if needed. All the commits must be made on top of master (fast-forward merge). CI must pass for changes to be accepted.