From 5e01ca29c5430fdc64ed5ba1d087ea8fd83b5cf7 Mon Sep 17 00:00:00 2001
From: Jelle Raaijmakers <jelle@gmta.nl>
Date: Tue, 28 Dec 2021 22:56:12 +0100
Subject: [PATCH] LibGL: Optimize float divisions in `unpack_color`

For Tux Racer on my machine, this function would account for 15% of
samples. After this change, that drops down to 9%.
---
 Userland/Libraries/LibSoftGPU/ImageFormat.h | 33 +++++++++++----------
 1 file changed, 17 insertions(+), 16 deletions(-)

diff --git a/Userland/Libraries/LibSoftGPU/ImageFormat.h b/Userland/Libraries/LibSoftGPU/ImageFormat.h
index 933627a10b..4f105646a4 100644
--- a/Userland/Libraries/LibSoftGPU/ImageFormat.h
+++ b/Userland/Libraries/LibSoftGPU/ImageFormat.h
@@ -36,41 +36,42 @@ inline static constexpr size_t element_size(ImageFormat format)
 
 inline static FloatVector4 unpack_color(void const* ptr, ImageFormat format)
 {
+    constexpr auto one_over_255 = 1.0f / 255;
     switch (format) {
     case ImageFormat::RGB888: {
         auto rgb = reinterpret_cast<u8 const*>(ptr);
         return {
-            rgb[0] / 255.f,
-            rgb[1] / 255.f,
-            rgb[2] / 255.f,
-            1.0f
+            rgb[0] * one_over_255,
+            rgb[1] * one_over_255,
+            rgb[2] * one_over_255,
+            1.0f,
         };
     }
     case ImageFormat::BGR888: {
         auto bgr = reinterpret_cast<u8 const*>(ptr);
         return {
-            bgr[2] / 255.f,
-            bgr[1] / 255.f,
-            bgr[0] / 255.f,
-            1.0f
+            bgr[2] * one_over_255,
+            bgr[1] * one_over_255,
+            bgr[0] * one_over_255,
+            1.0f,
         };
     }
     case ImageFormat::RGBA8888: {
         auto rgba = *reinterpret_cast<u32 const*>(ptr);
         return {
-            (rgba & 0xff) / 255.f,
-            ((rgba >> 8) & 0xff) / 255.f,
-            ((rgba >> 16) & 0xff) / 255.f,
-            ((rgba >> 24) & 0xff) / 255.f
+            (rgba & 0xff) * one_over_255,
+            ((rgba >> 8) & 0xff) * one_over_255,
+            ((rgba >> 16) & 0xff) * one_over_255,
+            ((rgba >> 24) & 0xff) * one_over_255,
         };
     }
     case ImageFormat::BGRA8888: {
         auto bgra = *reinterpret_cast<u32 const*>(ptr);
         return {
-            ((bgra >> 16) & 0xff) / 255.f,
-            ((bgra >> 8) & 0xff) / 255.f,
-            (bgra & 0xff) / 255.f,
-            ((bgra >> 24) & 0xff) / 255.f
+            ((bgra >> 16) & 0xff) * one_over_255,
+            ((bgra >> 8) & 0xff) * one_over_255,
+            (bgra & 0xff) * one_over_255,
+            ((bgra >> 24) & 0xff) * one_over_255,
         };
     }
     case ImageFormat::RGB565: {