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Denormalized floats

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FliegendeWurst 2020-05-18 09:00:23 +02:00
parent e32878d723
commit 0a8e357d3d
1 changed files with 12 additions and 7 deletions
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19
src/main.rs
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@ -41,8 +41,7 @@ fn interpret_single(float: u32) -> f32 {
if characteristic == 0 { if characteristic == 0 {
if mantissa != 0 { if mantissa != 0 {
eprintln!("can't process denormalized floats (yet)"); // denormalized value, handled below
return 0.0;
} else { } else {
return sign * 0.0; return sign * 0.0;
} }
@ -54,24 +53,30 @@ fn interpret_single(float: u32) -> f32 {
} }
} }
let mut power = 2.0f32.powi(characteristic as i32 - 127); let mut power = if characteristic != 0 { 2.0f32.powi(characteristic as i32 - 127) } else { 2.0f32.powi(-126) };
let mut value = sign * power; let mut value = if characteristic != 0 { power } else { 0.0 };
for idx in 0..23 { for idx in 0..23 {
let digit = (mantissa >> (22 - idx)) & 1; let digit = (mantissa >> (22 - idx)) & 1;
power /= 2.0; power /= 2.0;
if digit == 1 { if digit == 1 {
value += sign * power; value += power;
} }
} }
value value.copysign(sign)
} }
#[test] #[test]
fn interpret_single_test() { fn interpret_single_test() {
let tests = [ let tests = [
(0b1100_0000_1110_1000_0000_0000_0000_0000, -7.25), (0b1100_0000_1110_1000_0000_0000_0000_0000, -7.25),
(0b1011_1111_0101_0000_0000_0000_0000_0000, -0.8125) (0b1011_1111_0101_0000_0000_0000_0000_0000, -0.8125),
// denormalized float
(0b0000_0000_0100_0000_0000_0000_0000_0000, 0.000000000000000000000000000000000000005877472),
]; ];
// some sanity checks around subnormals
assert_eq!(2.0f32.powi(-127), tests[2].1);
assert_ne!(tests[2].1 / 2.0, 0.0);
assert_eq!(2.0f32.powi(-127) / 2.0, tests[2].1 / 2.0);
for test in &tests { for test in &tests {
assert_eq!(interpret_single(test.0), test.1); assert_eq!(interpret_single(test.0), test.1);
} }