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bugfix in mandelbrot-fixed 

Thanks to comparing regular ints with fixed-point ints, I was computing
iterations for many screenfuls of pixels to the right of the current one.
(Y-axis behaved similarly, but there it was just doing other work instead
of busy-looping forever. If you don't have anything else to do, it doesn't
matter what you do.)
This commit is contained in:
Kartik K. Agaram 2021-05-09 17:40:14 -07:00
parent cd6412129f
commit 4bfc80ce9a
1 changed files with 19 additions and 13 deletions
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32
mandelbrot-fixed.mu
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@ -112,20 +112,20 @@ fn mandelbrot screen: (addr screen) {
var a/eax: int <- copy 0
var b/ecx: int <- copy 0
a, b <- screen-size screen
var width-f/esi: int <- copy a
width-f <- shift-left 0xb/log2-font-width-and-fixed-precision # 3 + 8 = 11
var height-f/edi: int <- copy b
height-f <- shift-left 0xc/log2-font-height-and-fixed-precision # 4 + 8 = 12
var width/esi: int <- copy a
width <- shift-left 3/log2-font-width
var height/edi: int <- copy b
height <- shift-left 4/log2-font-height
var y/ecx: int <- copy 0
{
compare y, height-f
compare y, height
break-if->=
var imaginary-f/ebx: int <- viewport-to-imaginary-f y, width-f, height-f
var imaginary-f/ebx: int <- viewport-to-imaginary-f y, width, height
var x/eax: int <- copy 0
{
compare x, width-f
compare x, width
break-if->=
var real-f/edx: int <- viewport-to-real-f x, width-f
var real-f/edx: int <- viewport-to-real-f x, width
var iterations/esi: int <- mandelbrot-iterations-for-point real-f, imaginary-f, 0x400/max
compare iterations, 0x400/max
{
@ -202,10 +202,12 @@ fn mandelbrot-y x-f: int, y-f: int, imaginary-f: int -> _/ebx: int {
# ranges from -2 to +2. Viewport height just follows the viewport's aspect
# ratio.
fn viewport-to-real-f x: int, width-f: int -> _/edx: int {
fn viewport-to-real-f x: int, width: int -> _/edx: int {
# (x - width/2)*4/width
var result-f/eax: int <- int-to-fixed x
var half-width-f/ecx: int <- copy width-f
var width-f/ecx: int <- copy width
width-f <- shift-left 8/fixed-precision
var half-width-f/edx: int <- copy width-f
half-width-f <- shift-right-signed 1/log2
result-f <- subtract half-width-f
result-f <- shift-left 2/log4
@ -213,12 +215,16 @@ fn viewport-to-real-f x: int, width-f: int -> _/edx: int {
return result-f
}
fn viewport-to-imaginary-f y: int, width-f: int, height-f: int -> _/ebx: int {
fn viewport-to-imaginary-f y: int, width: int, height: int -> _/ebx: int {
# (y - height/2)*4/width
var result-f/eax: int <- int-to-fixed y
shift-right-signed height-f, 1/log2
result-f <- subtract height-f
var half-height-f/ecx: int <- copy height
half-height-f <- shift-left 8/fixed-precision
half-height-f <- shift-right-signed 1/log2
result-f <- subtract half-height-f
result-f <- shift-left 2/log4
var width-f/ecx: int <- copy width
width-f <- shift-left 8/fixed-precision
result-f <- divide-fixed result-f, width-f
return result-f
}