From 47c1398c6dd8d32801a250450eeccbce47eb5ba7 Mon Sep 17 00:00:00 2001
From: Bill Rossi <bassguitarbill@gmail.com>
Date: Thu, 21 Dec 2023 09:40:11 -0500
Subject: [PATCH] Assembly code is really fun
---
fasm/2015/1/problem.asm | 89 +++++++++++++++++++++++------------------
fasm/2015/2/problem.asm | 14 +++++--
fasm/lib/itoa.inc | 52 ++++++++++++++++++++++++
fasm/lib/print.inc | 5 +++
4 files changed, 118 insertions(+), 42 deletions(-)
diff --git a/fasm/2015/1/problem.asm b/fasm/2015/1/problem.asm
index eb35f24..bc02954 100644
--- a/fasm/2015/1/problem.asm
+++ b/fasm/2015/1/problem.asm
@@ -1,6 +1,7 @@
format ELF64 executable 3
include "lib/linux_syscall.inc"
include "lib/itoa.inc"
+include "lib/print.inc"
segment readable executable
entry main
@@ -20,6 +21,17 @@ main:
;; Close the input file
close [input_fd]
+ call part_1
+
+ call part_2
+
+ ;; Unmap the mapped file
+ munmap [input], [file_stat.st_size]
+
+ ;; Done!
+ exit 0
+
+part_1:
;; Setup the loop variables for counting
;; rbx starts at the first byte of input, and is incremented to read it all
mov rbx, [input]
@@ -28,42 +40,47 @@ main:
;; rdx counts down from the file's size to 0
mov rdx, [file_stat.st_size]
-lp:
+.lp:
;; Is the current character the "go up" character?
cmp byte [rbx], '('
;; If so, jump to "up"
- je up
+ je .up
;; Is the current character the "go down" character?
cmp byte [rbx], ')'
;; If so, it's the "go down" character, so decrement the current floor
- je down
+ je .down
;; Otherwise it's the EOF probably, skip it
- jmp other
-up:
+ jmp .other
+.up:
;; We should "go up", so increment the current floor
inc rcx
- jmp other
-down:
+ jmp .other
+.down:
;; We should "go down", so decrement the current floor
dec rcx
-other:
+.other:
;; Check the next character in the file
inc rbx
;; Count down the file's length
dec rdx
;; If we haven't reached the end of the file, loop
- jnz lp
+ jnz .lp
;; Put part 1's answer in rax
mov rax, rcx
- mov rbx, part_1
+
+ ;; Convert rax to a c string in rbx
+ mov rbx, part_1_answer
call itoa
- ;; Write part 1's verbiage to STDOUT
- write STDOUT, part_1_verbiage, 8
- write STDOUT, part_1, 6
- write STDOUT, newline, 1
+ ;; Print part 1's verbiage
+ mov rdi, part_1_verbiage
+ call print_c_string
+ call print_newline
+ ret
+
+part_2:
;; Setup the loop variables for counting
;; rbx starts at the first byte of input, and is incremented to read it all
mov rbx, [input]
@@ -71,44 +88,40 @@ other:
mov rcx, 0
;; rdx tracks how many steps we've made so far
mov rdx, 0
-lp2:
+.lp:
cmp byte [rbx], '('
- je up2
+ je .up
dec rcx
- jmp moved2
-up2:
+ jmp .moved
+.up:
inc rcx
-moved2:
+.moved:
inc rdx
cmp rcx, 0
- jl done
+ jl .done
inc rbx
- jnz lp2
-done:
+ jnz .lp
+.done:
;; Put part 2's answer in rax
mov rax, rdx
- mov rbx, part_2
+
+ ;; Convert rax to a c string in rbx
+ mov rbx, part_2_answer
call itoa
- ;; Write part 2's verbiage to STDOUT
- write STDOUT, part_2_verbiage, 8
- write STDOUT, part_2, 6
- write STDOUT, newline, 1
-
- ;; Unmap the mapped file
- munmap [input], [file_stat.st_size]
-
- ;; Done!
- exit 0
+ ;; Print part 2's verbiage
+ mov rdi, part_2_verbiage
+ call print_c_string
+ call print_newline
+ ret
segment readable writable
input_filename db '../data/2015/1/input.txt', 0
input_fd dq -1
input dq -1
-part_1_verbiage db 'Part 1: ', 0
-part_1 db ' ', 0
-part_2_verbiage db 'Part 2: ', 0
-part_2 db ' ', 0
-newline db 10
+part_1_verbiage db 'Part 1: '
+part_1_answer db ' ', 0
+part_2_verbiage db 'Part 2: '
+part_2_answer db ' ', 0
file_stat s_stat
diff --git a/fasm/2015/2/problem.asm b/fasm/2015/2/problem.asm
index 485ccbf..74dbd49 100644
--- a/fasm/2015/2/problem.asm
+++ b/fasm/2015/2/problem.asm
@@ -1,22 +1,28 @@
format ELF64 executable 3
include "lib/linux_syscall.inc"
include "lib/print.inc"
+include "lib/itoa.inc"
segment readable executable
entry main
main:
- mov rdi, input_filename
+ mov rax, 42069
+ mov rbx, part_1
+ call itoa
+
+ mov rdi, part_1_verbiage
call print_c_string
+
exit 0
segment readable writable
input_filename db '../data/2015/1/input.txt', 0, 'more text', 0
input_fd dq -1
input dq -1
-part_1_verbiage db 'Part 1: ', 0
-part_1 db ' ', 0
+part_1_verbiage db 'Part 1: '
+part_1 db ' ', 0
part_2_verbiage db 'Part 2: ', 0
-part_2 db ' ', 0
+part_2 db ' ', 0
newline db 10
file_stat s_stat
diff --git a/fasm/lib/itoa.inc b/fasm/lib/itoa.inc
index bf25fb7..9eab9bf 100644
--- a/fasm/lib/itoa.inc
+++ b/fasm/lib/itoa.inc
@@ -1,12 +1,21 @@
;; rax contains the integer
;; rbx contains a pointer to the string buffer
itoa:
+ ;; Fill 6 digits with zeroes
mov byte [rbx], '0'
mov byte [rbx + 1], '0'
mov byte [rbx + 2], '0'
mov byte [rbx + 3], '0'
mov byte [rbx + 4], '0'
mov byte [rbx + 5], '0'
+
+ ;; Special case for the number '0'
+ cmp rax, 0
+ jne .not_zero
+ mov byte [rbx + 1], 0
+ ret
+
+.not_zero:
sub rax, 100000
inc byte [rbx]
cmp rax, 0
@@ -42,4 +51,47 @@ itoa:
add rax, 10
dec byte [rbx + 4]
add [rbx + 5], rax
+
+
+ ;; Time to shift everything left
+ ;; End the current string with a null byte
+ mov byte [rbx + 6], 0
+.shift_left_loop:
+ cmp byte [rbx], '0'
+ jne .done
+
+ mov rcx, rbx
+ inc rcx
+ mov rdx, [rcx]
+ and rdx, 255
+ mov [rbx], dx
+
+ inc rcx
+ mov rdx, [rcx]
+ and rdx, 255
+ mov [rbx + 1], dx
+
+ inc rcx
+ mov rdx, [rcx]
+ and rdx, 255
+ mov [rbx + 2], dx
+
+ inc rcx
+ mov rdx, [rcx]
+ and rdx, 255
+ mov [rbx + 3], dx
+
+ inc rcx
+ mov rdx, [rcx]
+ and rdx, 255
+ mov [rbx + 4], dx
+
+ inc rcx
+ mov rdx, [rcx]
+ and rdx, 255
+ mov [rbx + 5], dx
+
+ jmp .shift_left_loop
+
+.done:
ret
diff --git a/fasm/lib/print.inc b/fasm/lib/print.inc
index fea16ee..a779072 100644
--- a/fasm/lib/print.inc
+++ b/fasm/lib/print.inc
@@ -31,3 +31,8 @@ print_c_string:
write STDOUT, r11, r12
ret
+
+newline db 10, 0
+print_newline:
+ write STDOUT, newline, 1
+ ret