From 572fade7ff3fb2b625a5479a9613c28f66c1185d Mon Sep 17 00:00:00 2001
From: "Justin C. Miller" <justin@devjustinian.com>
Date: Fri, 5 Feb 2021 23:55:42 -0800
Subject: [PATCH] [fb] Use rep stosl for screen fill

This is mostly cleanup after fighting the double buffering bug - bring
back rep stosl for screen fill, and move draw_pixel to be an inline
function.
---
 src/drivers/fb/screen.cpp | 15 +++++----------
 src/drivers/fb/screen.h   |  6 +++++-
 2 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/src/drivers/fb/screen.cpp b/src/drivers/fb/screen.cpp
index 3a95d7d..872e9ec 100644
--- a/src/drivers/fb/screen.cpp
+++ b/src/drivers/fb/screen.cpp
@@ -9,7 +9,8 @@ screen::screen(volatile void *addr, unsigned hres, unsigned vres, unsigned scanl
 	m_resx(hres),
 	m_resy(vres)
 {
-	m_back = reinterpret_cast<pixel_t*>(malloc(scanline*vres*sizeof(pixel_t)));
+	const size_t size = scanline * vres;
+	m_back = reinterpret_cast<pixel_t*>(malloc(size * sizeof(pixel_t)));
 }
 
 screen::pixel_t
@@ -33,15 +34,9 @@ screen::color(uint8_t r, uint8_t g, uint8_t b) const
 void
 screen::fill(pixel_t color)
 {
-	const size_t len = m_resx * m_resy;
-	for (size_t i = 0; i < len; ++i)
-		m_back[i] = color;
-}
-
-void
-screen::draw_pixel(unsigned x, unsigned y, pixel_t color)
-{
-	m_back[x + y * m_resx] = color;
+	const size_t len = m_scanline * m_resy;
+	asm volatile ( "rep stosl" : :
+		"a"(color), "c"(len), "D"(m_back) );
 }
 
 void
diff --git a/src/drivers/fb/screen.h b/src/drivers/fb/screen.h
index fbc9d82..b55903b 100644
--- a/src/drivers/fb/screen.h
+++ b/src/drivers/fb/screen.h
@@ -17,7 +17,11 @@ public:
 	pixel_t color(uint8_t r, uint8_t g, uint8_t b) const;
 
 	void fill(pixel_t color);
-	void draw_pixel(unsigned x, unsigned y, pixel_t color);
+
+	inline void draw_pixel(unsigned x, unsigned y, pixel_t color) {
+		const size_t index = x + y * m_scanline;
+		m_back[index] = color;
+	}
 
 	void update();