chapter 13, problem 2

Author: eliyanovva

readStr.asm

@@ -0,0 +1,153 @@
+section .data
+
+; Define standard constants
+
+LF equ 10 ; line feed
+NULL equ 0 ; end of string
+TRUE equ 1
+FALSE equ 0
+
+EXIT_SUCCESS equ 0 ; success code
+
+STDIN equ 0 ; standard input
+STDOUT equ 1 ; standard output
+STDERR equ 2 ; standard error
+
+SYS_read equ 0 ; read
+SYS_write equ 1 ; write
+SYS_open equ 2 ; file open
+SYS_close equ 3 ; file close
+SYS_fork equ 57 ; fork
+SYS_exit equ 60 ; terminate
+SYS_creat equ 85 ; file open/create
+SYS_time equ 201 ; get time
+
+STRLEN equ 51 ; The string length includes the terminating Null character
+
+pmpt db "Enter Text: ", NULL ;
+newLine db LF, NULL
+
+section .bss
+chr resb 1
+str1 resb STRLEN+1
+str2 resb STRLEN+1
+
+section .text
+
+global _start
+_start:
+
+    mov rsi, STRLEN
+    mov rdi, str1
+    call readString
+
+    mov rsi, STRLEN
+    mov rdi, str2
+    call readString
+
+exampleDone:
+    mov rax, SYS_exit
+    mov rdi, EXIT_SUCCESS
+    syscall
+
+; FUNCTION INPUT:
+;   rsi contains the max length of the string
+;   rdi contains the string address
+
+global readString
+readString:
+; Display prompt
+    push rdi
+    mov rdi, pmpt
+    call printString
+    pop rdi
+
+; Read characters from user
+
+    mov rbx, rdi
+    mov r12, 0
+    mov r8, rsi ; store max length in r8
+    mov r9, rdi ; store string address in r9
+
+readCharacters:
+    mov rax, SYS_read ; system code for read
+    mov rdi, STDIN ; standard in
+    lea rsi, byte[chr] ; address of chr (defined in the data section)
+    mov rdx, 1 ; count
+    syscall
+
+    mov al, byte[chr] ; get character
+    cmp al, LF ; compare input character to \n
+    je readDone ; finish reading if equal
+
+    inc r12 ; count++
+    cmp r12, r8 ; if #characters is more than max length, stop placing in the buffer
+    jae readCharacters
+
+    mov byte[rbx], al ; store character on the input address
+    inc rbx ; update address for the next character
+
+    jmp readCharacters
+
+readDone:
+    mov byte[rbx], NULL ; NULL termination
+    ; Output line
+
+    mov rdi, r9 ; print the string on the console
+    call printString
+    mov rax, r12 ; return the number of characters without NULL
+
+    ret
+
+; print string function, the string should be null terminated
+; arguments: address, string
+
+global printString
+printString:
+    push rbx
+    mov rbx, rdi
+    mov rdx, 0
+
+strCountLoop:
+    cmp byte[rbx], NULL
+    je strCountDone
+    inc rdx
+    inc rbx
+    jmp strCountLoop
+
+strCountDone:
+    cmp rdx, 0
+    je printDone
+; Call OS to output string
+    mov rax, SYS_write
+    mov rsi, rdi
+    mov rdi, STDOUT
+
+    syscall
+
+printDone:
+    pop rbx
+    ret
+
+; find string length
+; input is the address where the length is stored in rdi
+; output is the length in rax
+
+strLen:
+    push rbx
+    push rdx
+    mov rbx, rdi
+    mov rdx, 0
+
+CountLoop:
+    cmp byte[rbx], NULL
+    je funcStrLenDone
+    inc rdx
+    inc rbx
+    jmp CountLoop
+
+funcStrLenDone:
+    mov rax, rdx ; store the string length in rax
+    pop rdx
+    pop rbx
+    ret