From 2de764203d46c9fe6b506ec070f399439ab7ce09 Mon Sep 17 00:00:00 2001
From: John Tsiombikas <nuclear@member.fsf.org>
Date: Thu, 27 Feb 2020 20:13:11 +0200
Subject: [PATCH] done

---
 dos1/c.asm |  119 ++++++++++++++++++++++++++++++++----------------------------
 1 file changed, 64 insertions(+), 55 deletions(-)

diff --git a/dos1/c.asm b/dos1/c.asm
index 78a0946..c3c62c9 100644
--- a/dos1/c.asm
+++ b/dos1/c.asm
@@ -1,5 +1,12 @@
-; Lowest yet: 265
-
+; Sierpbounceski / Mindlapse
+; --------------------------
+; Sierpinski fractal, bummed to 253b down from the 416b initial version
+; Author: John Tsiombikas (Nuclear / Mindlapse) <nuclear@member.fsf.org>
+; This code is public domain
+; --------------------------
+; Build for DOS: nasm -o sierpb.com -f bin sierpb.asm
+; Build as boot sector: nasm -o sierpb.img -f bin -DBOOTSECT sierpb.asm
+; --------------------------
 	bits 16
 %ifdef BOOTSECT
 	org 7c00h
@@ -23,6 +30,18 @@ SIERP_VERTS equ code_end + 8
 	jz .notblank	; loop while vblank bit is 0 (visible area)
 %endmacro
 
+%macro RAND 0
+	; random number generator
+	mov ax, [randval]
+	mov bx, ax
+	shr bx, 7
+	xor ax, bx
+	mov bx, ax
+	shl bx, 9
+	xor ax, bx
+	mov [randval], ax
+%endmacro
+
 
 start:
 %ifdef BOOTSECT
@@ -31,8 +50,7 @@ start:
 	mov es, ax
 	mov ss, ax
 	jmp 00:.setcs
-.setcs:
-	mov sp, 0
+.setcs: xor sp, sp
 %endif
 	mov al, 13h
 	int 10h
@@ -43,7 +61,35 @@ start:
 	mov es, ax
 
 mainloop:
-	call animate
+	; --- animate start ---
+	mov cx, 3
+	mov di, sierp_verts
+	mov si, sierp_vel
+.loop:
+	mov bx, 4
+.xyloop:
+	mov ax, [di]		; grab vertex X
+	add ax, [si]		; add velocity X
+	jl .xout
+	cmp ax, [bx + bounds - 2]
+	jge .xout
+	jmp .skip_xflip
+.xout:
+	sub ax, [si]		; revert to previous X
+	neg word [si]		; negate velocity X
+.skip_xflip:
+	mov [di], ax		; update vertex X
+
+	; to do the same for Y increment edi and esi by 2
+	add di, 2
+	add si, 2
+	sub bx, 2
+	jnz .xyloop
+
+	dec cx
+	jnz .loop
+	; --- animate end ---
+
 
 	; clear the framebuffer
 	mov al, 128
@@ -51,25 +97,26 @@ mainloop:
 	xor di, di
 	rep stosb
 
+	mov si, setcol + 1
 	; draw shadow
-	mov si, 5
-	mov byte [setcol + 1], 199	; shadow color
+	mov bp, 5
+	mov byte [si], 199	; shadow color
 	call drawsierp
 	; draw fractal
-	xor si, si
-	mov byte [setcol + 1], 2	; fractal color
+	xor bp, bp
+	mov byte [si], 48h	; fractal color
 	call drawsierp
 
 	; copy framebuffer to video ram
 	push ds
 	push es
-	; point ds:si (source) to es:0
-	mov ax, es
-	mov ds, ax
+	; point ds:si (source) to es:0 (framebuffer)
+	push es
+	pop ds
 	xor si, si
 	; point es:di (dest) to a000:0
-	mov ax, 0a000h
-	mov es, ax
+	push word 0a000h
+	pop es
 	xor di, di
 	mov cx, 32000
 	WAIT_VBLANK
@@ -101,7 +148,7 @@ drawsierp:
 	; number of iterations in cx
 	mov cx, NUM_POINTS
 dsloop:	; pick a vertex at random and move half-way there
-	call rand
+	RAND
 	mov bx, 3
 	xor dx, dx
 	div bx	; dx is now rand % 3
@@ -119,7 +166,7 @@ dsloop:	; pick a vertex at random and move half-way there
 	add ax, [SIERP_PT + 2]
 	shr ax, 1
 	mov [SIERP_PT + 2], ax	; store the reuslting Y back to [SIERP_PT + 2]
-	add ax, si	; add offset
+	add ax, bp	; add offset
 	mov bx, ax
 	shl ax, 8
 	shl bx, 6
@@ -143,46 +190,8 @@ bounds	dw 200 - SHADOW_OFFS
 	dw 320 - SHADOW_OFFS
 
 
-animate:
-	mov cx, 3
-	mov di, sierp_verts
-	mov si, sierp_vel
-.loop:
-	mov bx, 4
-.xyloop:
-	mov ax, [di]		; grab vertex X
-	add ax, [si]		; add velocity X
-	jl .xout
-	cmp ax, [bx + bounds - 2]
-	jge .xout
-	jmp .skip_xflip
-.xout:
-	sub ax, [si]		; revert to previous X
-	neg word [si]		; negate velocity X
-.skip_xflip:
-	mov [di], ax		; update vertex X
-
-	; to do the same for Y increment edi and esi by 2
-	add di, 2
-	add si, 2
-	sub bx, 2
-	jnz .xyloop
-
-	dec cx
-	jnz .loop
-	ret
-
 	; random number generator
-rand:
-	mov ax, [randval]
-	mov bx, ax
-	shr bx, 7
-	xor ax, bx
-	mov bx, ax
-	shl bx, 9
-	xor ax, bx
-	mov [randval], ax
-	ret
+;rand:
 ;	mov eax, [RANDVAL]
 ;	mul dword [randmul]
 ;	add eax, 12345
-- 
1.7.10.4