From a9ef0dce69aba09e56b6a3547ae45be4da54ce56 Mon Sep 17 00:00:00 2001
From: Bill Rossi <bassguitarbill@gmail.com>
Date: Thu, 21 Dec 2023 11:45:43 -0500
Subject: [PATCH] Implement atoi

---
 fasm/2015/2/problem.asm | 31 ++++++++++++++++++-------------
 fasm/lib/itoa.inc       | 28 ++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+), 13 deletions(-)

diff --git a/fasm/2015/2/problem.asm b/fasm/2015/2/problem.asm
index 74dbd49..2a461b0 100644
--- a/fasm/2015/2/problem.asm
+++ b/fasm/2015/2/problem.asm
@@ -2,27 +2,32 @@ format ELF64 executable 3
 include "lib/linux_syscall.inc"
 include "lib/print.inc"
 include "lib/itoa.inc"
+include "lib/file.inc"
 
 segment readable executable
 entry main
 
 main:
-	mov rax, 42069
-	mov rbx, part_1
-	call itoa
+	mov rdi, input_filename
+	call load_file
 
-	mov rdi, part_1_verbiage
-	call print_c_string
+	call part_1
 
 	exit 0
 
+part_1:
+	mov rdi, number
+	call atoi
+	mov rbx, part_1_answer
+	call itoa
+	mov rdi, part_1_verbiage
+	call print_c_string
+	ret
+
 segment readable writable
-input_filename db '../data/2015/1/input.txt', 0, 'more text', 0
-input_fd dq -1
-input dq -1
+input_filename db '../data/2015/2/input.txt', 0
 part_1_verbiage db 'Part 1: '
-part_1 db '      ', 0
-part_2_verbiage db 'Part 2: ', 0
-part_2 db '      ', 0
-newline db 10
-file_stat s_stat
+part_1_answer db '      ', 0
+part_2_verbiage db 'Part 2: '
+part_2_answer db '      ', 0
+number db '42069', 0
diff --git a/fasm/lib/itoa.inc b/fasm/lib/itoa.inc
index de3293f..b0fe7a9 100644
--- a/fasm/lib/itoa.inc
+++ b/fasm/lib/itoa.inc
@@ -87,3 +87,31 @@ itoa:
 
 .done:
    ret
+
+;;; rdi should contain the address of a c-string
+atoi:
+	mov r8, rdi
+	mov rax, 0
+	mov rcx, 10
+
+.lp:
+	cmp byte [r8], 0
+	jz .done
+	mov r9, [r8]
+	and r9, 127
+	sub r9, '0'
+	add rax, r9
+	mov rcx, rax
+	add rax, rax
+	add rax, rax
+	add rax, rax
+	add rax, rcx
+	add rax, rcx
+	inc r8
+	jmp .lp
+
+.done:
+	mov rcx, 10
+	mov rdx, 0
+	div rcx
+	ret