diff --git a/common/src/util/mod.rs b/common/src/util/mod.rs index 09fb4d6acc..cb443ef2fd 100644 --- a/common/src/util/mod.rs +++ b/common/src/util/mod.rs @@ -2,6 +2,39 @@ pub const GIT_HASH: &str = include_str!(concat!(env!("OUT_DIR"), "/githash")); use vek::{Mat3, Rgb, Rgba, Vec3}; +/// This is a fast approximation of powf. This should only be used when minor accuracy loss is acceptable. +#[inline(always)] +#[allow(unsafe_code)] +fn approx_powf(b: f32, e: f32) -> f32 { + unsafe { + let b = b as f64; + let e = e as f64; + union Swagger { + f: f64, + a: [i32; 2], + } + let mut b = Swagger { f: b }; + b.a[1] = (e * (b.a[1] as f64 - 1072632447.0) + 1072632447.0) as i32; + b.a[0] = 0; + b.f as f32 + } +} + +#[cfg(test)] +mod approx_powf_tests { + fn close_ei(a: f32, b: f32) -> bool { + (a - b < 1.0 && a - b > 0.0) || (b - a < 1.0 && b - a > 0.0) + } + + #[test] + fn accuracy_1() { + let test_values: Vec = vec![3.0, 2.5, 1.5, 2.2]; + test_values.windows(2).for_each(|a| { + assert!(close_ei(a[0].powf(a[1]), super::approx_powf(a[0], a[1]))); + }); + } +} + #[inline(always)] pub fn srgb_to_linear(col: Rgb) -> Rgb { #[inline(always)] @@ -9,7 +42,7 @@ pub fn srgb_to_linear(col: Rgb) -> Rgb { if x <= 0.04045 { x / 12.92 } else { - ((x + 0.055) / 1.055).powf(2.4) + approx_powf((x + 0.055) / 1.055, 2.4) } } col.map(to_linear) @@ -21,7 +54,7 @@ pub fn linear_to_srgb(col: Rgb) -> Rgb { if x <= 0.0031308 { x * 12.92 } else { - x.powf(1.0 / 2.4) * 1.055 - 0.055 + approx_powf(x, 1.0 / 2.4) * 1.055 - 0.055 } } col.map(to_srgb) @@ -118,6 +151,7 @@ pub fn xyy_to_rgb(xyy: Vec3) -> Rgb { ) } +// TO-DO: speed this up #[inline(always)] pub fn saturate_srgb(col: Rgb, value: f32) -> Rgb { let mut hsv = rgb_to_hsv(srgb_to_linear(col));