From 29771ce1657c18e9e8d49a2e1128b76d1a16d4f8 Mon Sep 17 00:00:00 2001
From: Gray Olson <gray@grayolson.com>
Date: Tue, 10 Nov 2020 14:32:05 -0700
Subject: [PATCH 1/2] add trunc and fract to MathExt

---
 crates/spirv-std/src/math_ext.rs | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/crates/spirv-std/src/math_ext.rs b/crates/spirv-std/src/math_ext.rs
index f196cd086c..c5b5495d9d 100644
--- a/crates/spirv-std/src/math_ext.rs
+++ b/crates/spirv-std/src/math_ext.rs
@@ -11,6 +11,8 @@ pub trait MathExt {
     fn ceil(self) -> Self;
     fn exp(self) -> Self;
     fn saturate(self) -> Self;
+    fn trunc(self) -> Self;
+    fn fract(self) -> Self;
 
     fn signum(self) -> Self;
     fn copysign(self, sign: Self) -> Self;
@@ -71,6 +73,14 @@ impl MathExt for f32 {
         self.max(0.0).min(1.0)
     }
 
+    fn trunc(self) -> f32 {
+        unsafe { core::intrinsics::truncf32(self) }
+    }
+
+    fn fract(self) -> f32 {
+        self - self.trunc()
+    }
+
     fn signum(self) -> f32 {
         if self.is_nan() {
             Self::NAN

From 5ed98c4cf581e251cc58245707550ede52d5889d Mon Sep 17 00:00:00 2001
From: Gray Olson <gray@grayolson.com>
Date: Tue, 10 Nov 2020 15:13:31 -0700
Subject: [PATCH 2/2] add step, step_select, and mix to MathExt

---
 crates/spirv-std/src/math_ext.rs | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/crates/spirv-std/src/math_ext.rs b/crates/spirv-std/src/math_ext.rs
index c5b5495d9d..a8b296e0d2 100644
--- a/crates/spirv-std/src/math_ext.rs
+++ b/crates/spirv-std/src/math_ext.rs
@@ -17,6 +17,14 @@ pub trait MathExt {
     fn signum(self) -> Self;
     fn copysign(self, sign: Self) -> Self;
 
+    /// Returns `0.0` if `self < edge` and 1.0 otherwise.
+    fn step(self, edge: Self) -> Self;
+    /// Selects between `less` and `greater_or_equal` based on the result of `self < edge`
+    fn step_select(self, edge: Self, less: Self, greater_or_equal: Self) -> Self;
+    /// Performs a linear interpolation between `self` and `other` using `a` to weight between them.
+    /// The return value is computed as `self * (1−a) + other * a`.
+    fn mix(self, other: Self, a: Self) -> Self;
+
     // TODO: implement but need new intrinsic in core?
     //fn tan(self) -> Self;
 }
@@ -92,4 +100,24 @@ impl MathExt for f32 {
     fn copysign(self, sign: f32) -> f32 {
         unsafe { core::intrinsics::copysignf32(self, sign) }
     }
+
+    fn step(self, edge: f32) -> f32 {
+        if self < edge {
+            0.0
+        } else {
+            1.0
+        }
+    }
+
+    fn step_select(self, edge: f32, less: f32, greater_or_equal: f32) -> f32 {
+        if self < edge {
+            less
+        } else {
+            greater_or_equal
+        }
+    }
+
+    fn mix(self, other: f32, a: f32) -> f32 {
+        self - (self + other) * a
+    }
 }