From b4533c4a1216e74b55a589c659690a8429c47c1f Mon Sep 17 00:00:00 2001
From: Ian McKellar <ian@mckellar.org>
Date: Wed, 4 Dec 2019 14:27:06 -0800
Subject: [PATCH] day 4.2: dos asm

---
 04-dos-asm/Makefile  |   5 +-
 04-dos-asm/part2.asm | 140 +++++++++++++++++++++++++++++++++++++++++++
 04-dos-asm/part2.com | Bin 0 -> 216 bytes
 3 files changed, 144 insertions(+), 1 deletion(-)
 create mode 100644 04-dos-asm/part2.asm
 create mode 100644 04-dos-asm/part2.com

diff --git a/04-dos-asm/Makefile b/04-dos-asm/Makefile
index 35f4165..6c10a8f 100644
--- a/04-dos-asm/Makefile
+++ b/04-dos-asm/Makefile
@@ -1,7 +1,10 @@
-all: part1.com
+all: part1.com part2.com
 
 %.com: %.asm
 	nasm -o $@ $+
 
 run1: part1.com
 	dosbox part1.com
+
+run2: part2.com
+	dosbox part2.com
diff --git a/04-dos-asm/part2.asm b/04-dos-asm/part2.asm
new file mode 100644
index 0000000..53e3b91
--- /dev/null
+++ b/04-dos-asm/part2.asm
@@ -0,0 +1,140 @@
+section .text
+org 0x100
+
+
+main_loop:
+
+	; make sure digits aren't descending
+	mov bx, 0
+ascending_loop:
+	mov al, byte [number+0+bx]
+	cmp al, byte [number+1+bx]
+	jg thank_u_next
+	inc bx
+	cmp bx, 5
+	jne ascending_loop
+
+adjacent:
+	; find adjacent digits
+	mov bx, 0
+adjacent_loop:
+	mov al, byte [number+bx]
+	cmp al, byte [number+bx+1]
+	je found_adjacent
+continue_adjacent:
+	inc bx
+	cmp bx, 5
+	jne adjacent_loop
+	jmp thank_u_next
+
+skip_rest_of_group:
+	inc bx
+	cmp bx, 5
+	je thank_u_next
+	mov al, byte [number+bx]
+	cmp al, byte [number+bx+1]
+	je skip_rest_of_group
+	jmp adjacent_loop
+
+found_adjacent:
+	mov al, byte [number+bx]
+	cmp al, byte [number+bx+2]
+	je skip_rest_of_group ; group of 3 or more
+	; found exactly two
+	jmp found
+
+found:
+	; found an answer!
+	mov di, count
+	call increment_number
+	jmp thank_u_next
+
+	mov di, number
+	call print_number
+
+thank_u_next:
+; increment nuber
+	mov di, number
+	call increment_number
+
+; loop if we haven't reached 789857
+	cmp byte [number+0], 7
+	jne main_loop
+	cmp byte [number+1], 8
+	jne main_loop
+	cmp byte [number+2], 9
+	jne main_loop
+	cmp byte [number+3], 8
+	jne main_loop
+	cmp byte [number+4], 5
+	jne main_loop
+	cmp byte [number+5], 7
+	jne main_loop
+
+	jmp exit
+
+
+
+; increment the number
+increment_number:
+	; bl holds the digit number
+	mov bx, 5
+increment_number_loop:
+	inc byte [di + bx]
+	cmp byte [di + bx], 10
+	jne increment_number_done
+	; digit overflowed
+	mov byte [di + bx], 0
+	cmp bx, 0
+	je increment_number_overflow
+	dec bx
+	jmp increment_number_loop
+increment_number_done:
+	ret
+increment_number_overflow:
+	; panic
+	int 3
+
+; prints the number
+print_number:
+	mov bx, 0
+print_number_loop:
+	; load next digit
+	mov dl, [ds:di + bx]
+	; make it ascii
+	add dl, '0'
+	; print to stdout
+	mov ah, 0x02
+	int 0x21
+
+	inc bl
+	cmp bl, 6
+	jne print_number_loop
+
+	; print crlf
+	mov ah, 0x9
+	mov dx, crlf
+	int 0x21
+	ret
+	
+
+
+
+exit:
+
+	mov di, count
+	call print_number
+
+	mov	ax, 0x4c00
+	int	0x21
+
+section .data
+; constants
+crlf: db 13, 10, '$'
+
+; number digits
+number: db 2, 4, 0, 9, 2, 0
+past_the_number: db 0xff ; to make comparisons simpler
+
+; number of possible passwords
+count: db 0, 0, 0, 0, 0, 0
\ No newline at end of file
diff --git a/04-dos-asm/part2.com b/04-dos-asm/part2.com
new file mode 100644
index 0000000000000000000000000000000000000000..14a6eeb49dc20d89f8d88334c64fe4820ebbe8b7
GIT binary patch
literal 216
zcmdnZz|hrxn$fEL3}d~!bMtT3(hs{4LM2iVq1QSfx<n18wB*C<I}r9+#*!zm8TMad
zd||`znr;7S#uq*eAX1N^!R|C8d+GcJyEBX&r864r&N6bAPHeC{2jq1%*qvu&Ep2YF
zyTHiK-&*zmwaIQ)hJTC=mRzOW#~2x!e>0S@c)xyk_$)KfF?L;o4TlW2Fr8KWcevp<
nTj~2PoV!jio>e>yvi08o9SlBa6&ZNBRG3&8IGGs!Gk^gAc63<A

literal 0
HcmV?d00001

-- 
2.45.2