str_lib.asm

; =========================================================================
; PROGRAMMER    : Nicholas Perry
; FILE          : str_lib.asm
; DATE          : 2005-09-06 
; SUBJECT       : lab#4 
; my personal library of string functions I made to help myself in micro course
; =========================================================================

		; Declare the C file handling functions.
		EXTERN  _printf
            EXTERN  _getchb
		EXTERN	_putch

            GLOBAL  String_Length
		GLOBAL	String_Copy
		GlOBAL	String_Cat
		GLOBAL	String_Search

	
        
CR		EQU	13
LF		EQU	10

;---------------------------------
;           Data Segment
;---------------------------------
                SECTION .data

	;; Declare needed variables here.
	
copy_eax	DD	0	; This file pointer is used to access the 
copy_ebx	DD	0	; This file pointer is used to access the 
copy_ecx	DD	0	; This file pointer is used to access the 
copy_edx	DD	0	; This file pointer is used to access the 
copy_esi	DD	0	; This file pointer is used to access the 
copy_edi	DD	0	; This file pointer is used to access the 
	
	
;-------------------------------------------         
;           Block Storage Segment
;-------------------------------------------

                SECTION .bss

	;; These should be the only uninitialized buffers you need.
	


;---------------------------------
;           Code Segment
;---------------------------------

                SECTION .text
	
  
String_Length
	;; Returns number of characters in a null
	;; terminated string pointed to by esi.
	;; Return Location: eax
	;; Does not change any other registers

	;; Copy out registers, just in case
	push esi

	mov eax, DWORD 0
lenfindloop:
	cmp [esi], BYTE 0 	; See if cur char is null.
	je endlenfindloop	; If is, stop searching.
	inc eax			; else, count as char.
	inc esi			; Goto next letter
	jmp lenfindloop		; Repeat
endlenfindloop:
	pop esi
	ret
	
String_Copy
	;; Copys the null terminated string found
	;; as a refrence from esi, to the refrence
	;; from edi
	;; Returns the number of bytes copied
	;; not including null char.
	;; Return Location eax
	;; Does not change any other registers

	;; Copy out registers, just in case
	push ecx
	push ebx
	push edi
	push esi

	;; Find string length
	push esi
	call String_Length
	pop esi

	mov ecx,eax		; Move string length to counter.
	mov eax,DWORD 0		; Start Byte count at 0
stringcopyloop:
	mov bl,BYTE [esi]	; Move letter from loc esi to loc esi.
	mov [edi], bl
	inc eax			; Count letter
	inc edi			; Next letter
	inc esi
	loop stringcopyloop	; keep going till at end
	mov [edi],DWORD 0	; Place null char.
	pop esi
	pop edi
	pop ebx
	pop ecx

	ret

	
String_Cat
	;; Concatanates null terminated string
	;; in esi onto the end of edi
	;; Returns the number of bytes copied,
	;; not including null char into eax

	;; Copy out registers, just in case
	push ecx
	push ebx
	push edi
	push esi

	;; Find end of destination
	mov esi, edi
	call String_Length
	add edi, eax	

	pop esi			; restore esi to previous source
	push esi
	
	;; Find string length to copy
	push esi
	call String_Length
	pop esi

	mov ecx,eax		; Move string length to counter.
	mov eax,DWORD 0		; Start Byte count at 0
stringcatloop:
	mov bl,BYTE [esi]	; Move letter from loc esi to loc esi.
	mov [edi], bl
	inc eax			; Count letter
	inc edi			; Next letter
	inc esi
	loop stringcatloop	; keep going till at end
	mov [edi],DWORD 0	; Place null char.
	pop esi
	pop edi
	pop ebx
	pop ecx

	ret
	
String_Search
	;; Searches null terminated string 
	;; from esi, looking for char in al,
	;; Returns a pointer to that char,
	;; or Null pointer if not found, into eax
	
	;; Copy out registers, just in case
	push ebx
	push ecx	
	push edi
	push eax
	
	mov edi, esi		; SCASB uses edi, not esi...
	call String_Length	; Find length of string
	mov ecx, eax		; store length as counter
	inc ecx
	mov ebx, eax		; store length
	
	pop eax			; restore eax to letter

	cld 			; auto increment?
	REPNE SCASB		; keep going while not found al in edi
	cmp ecx, DWORD 0
	je notfound
	
	;; length - ecx = offset,

	sub ebx, ecx 		; Find position of letter, if found
	
	mov eax, ebx		; move to return value
	add eax, esi		; change offset to pointer
	jmp found
	
notfound:
	xor eax,eax		; I'm an uber1337 assembler monkey.
found:		
	pop edi
	pop ecx
	pop ebx
        ret