[SLOF] [PATCH 2/4] fbuffer: Precalculate line length in bytes

[Thomas Huth]

The framebuffer code calculates the length of a line in bytes over
and over again, even in the tight innermost loops of the drawing
functions. We can easily avoid this multiplication and make the
code more readable by storing this value in a variable instead.

Signed-off-by: Thomas Huth <thuth at redhat.com>
---
 slof/fs/fbuffer.fs | 25 ++++++++++++++-----------
 1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/slof/fs/fbuffer.fs b/slof/fs/fbuffer.fs
index bfe7ebf..4704608 100644
--- a/slof/fs/fbuffer.fs
+++ b/slof/fs/fbuffer.fs
@@ -19,6 +19,7 @@
 0 VALUE screen-height
 0 VALUE screen-width
 0 VALUE screen-depth
+0 VALUE screen-line-bytes
 0 VALUE window-top
 0 VALUE window-left
 
@@ -54,10 +55,10 @@
 : fb8-background inverse? ;
 : fb8-foreground inverse? invert ;
 
-: fb8-lines2bytes ( #lines -- #bytes ) char-height * screen-width * screen-depth * ;
+: fb8-lines2bytes ( #lines -- #bytes ) char-height * screen-line-bytes * ;
 : fb8-columns2bytes ( #columns -- #bytes ) char-width * screen-depth * ;
 : fb8-line2addr ( line# -- addr )
-	char-height * window-top + screen-width * screen-depth *
+	char-height * window-top + screen-line-bytes *
 	frame-buffer-adr + window-left screen-depth * +
 ;
 
@@ -98,10 +99,10 @@ CREATE bitmap-buffer 400 4 * allot
 
 : fb8-toggle-cursor ( -- )
 	line# fb8-line2addr column# fb8-columns2bytes +
-	char-height 2 - screen-width screen-depth * * +
+	char-height 2 - screen-line-bytes * +
 	2 0 ?DO
 		dup char-width screen-depth * invert-region
-		screen-width screen-depth * +
+		screen-line-bytes +
 	LOOP drop
 ;
 
@@ -111,7 +112,7 @@ CREATE bitmap-buffer 400 4 * allot
 	line# fb8-line2addr column# fb8-columns2bytes + ( bitmap-buf fb-addr )
 	char-height 0 ?DO
 		2dup char-width screen-depth * mrmove
-		screen-width screen-depth * + >r char-width screen-depth * + r>
+		screen-line-bytes + >r char-width screen-depth * + r>
 	LOOP 2drop
     ELSE 2drop r> 3drop THEN
 ;
@@ -136,12 +137,12 @@ CREATE bitmap-buffer 400 4 * allot
 		fb8-columns2bytes swap fb8-columns2bytes tuck -
 		over r@ tuck + rot char-height 0 ?DO
 			3dup rmove
-			-rot screen-width screen-depth * tuck + -rot + swap rot
+			-rot screen-line-bytes tuck + -rot + swap rot
 		LOOP
 		3drop r>
 	THEN
 	char-height 0 ?DO
-		dup 2 pick fb8-erase-block screen-width screen-depth * +
+		dup 2 pick fb8-erase-block screen-line-bytes +
 	LOOP
 	2drop
 ;
@@ -154,12 +155,12 @@ CREATE bitmap-buffer 400 4 * allot
 		fb8-columns2bytes swap fb8-columns2bytes tuck -
 		over r@ + 2dup + r> swap >r rot char-height 0 ?DO
 			3dup rmove
-			-rot screen-width screen-depth * tuck + -rot + swap rot
+			-rot screen-line-bytes tuck + -rot + swap rot
 		LOOP
 		3drop r> over -
 	THEN
 	char-height 0 ?DO
-		dup 2 pick fb8-erase-block screen-width screen-depth * +
+		dup 2 pick fb8-erase-block screen-line-bytes +
 	LOOP
 	2drop
 ;
@@ -167,11 +168,11 @@ CREATE bitmap-buffer 400 4 * allot
 : fb8-reset-screen ( -- ) ( Left as no-op by design ) ;
 
 : fb8-erase-screen ( -- )
-	frame-buffer-adr screen-height screen-width * screen-depth * fb8-erase-block
+	frame-buffer-adr screen-height screen-line-bytes * fb8-erase-block
 ;
 
 : fb8-invert-screen ( -- )
-	frame-buffer-adr screen-height screen-width * screen-depth * invert-region
+	frame-buffer-adr screen-height screen-line-bytes * invert-region
 ;
 
 : fb8-blink-screen ( -- ) fb8-invert-screen fb8-invert-screen ;
@@ -179,6 +180,7 @@ CREATE bitmap-buffer 400 4 * allot
 : fb8-install ( width height #columns #lines -- )
 	1 to screen-depth
 	2swap  to screen-height  to screen-width
+	screen-width to screen-line-bytes
 	screen-#rows min to #lines
 	screen-#columns min to #columns
 	screen-height char-height #lines * - 2/ to window-top
@@ -200,6 +202,7 @@ CREATE bitmap-buffer 400 4 * allot
 	>r
 	fb8-install
 	r> to screen-depth
+	screen-width screen-depth * to screen-line-bytes
 ;
 
 
-- 
1.8.3.1