[PPV2] PPB-61 Fixed issue with FastSign() on WebGL/Safari (#8171)

* Fixed issue with `FastSign()` on WebGL/Safari

* Update CHANGELOG

* Update CHANGELOG

---------

Co-authored-by: Théo Penavaire <[email protected]>

Author: BenGraterUnity

com.unity.postprocessing/CHANGELOG.md

@@ -4,13 +4,14 @@ All notable changes to this package will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
-## [3.5.0] - 2025-06-12
+## [3.5.0] - 2025-06-18
 
 ### Added
 - Added Switch2 platform support
 
 ### Fixed
 - Remove support for PVRTC format in Unity 6.1 or newer
+- Fixed issue with FastSign on WebGL/Safari (IN-71005)
 - Fixed compute based effects not supported on OpenGLES
 - Documentation updates
 

com.unity.postprocessing/PostProcessing/Shaders/Colors.hlsl

@@ -597,7 +597,7 @@ float3 LiftGammaGainHDR(float3 c, float3 lift, float3 invgamma, float3 gain)
 
     // ACEScg will output negative values, as clamping to 0 will lose precious information we'll
     // mirror the gamma function instead
-    return FastSign(c) * pow(abs(c), invgamma);
+    return sign(c) * pow(abs(c), invgamma);
 }
 
 //

com.unity.postprocessing/PostProcessing/Shaders/StdLib.hlsl

@@ -116,6 +116,7 @@ float4 Max3(float4 a, float4 b, float4 c)
 
 // https://twitter.com/SebAaltonen/status/878250919879639040
 // madd_sat + madd
+// Incorrect result on WebGL/Safari with A17 or M3 processors.
 float FastSign(float x)
 {
     return saturate(x * FLT_MAX + 0.5) * 2.0 - 1.0;