;***********************************************
;程序名稱：演示Base64編碼/解碼原理
;作者：羅聰
;日期：2002-9-14
;出處：http://laoluoc.yeah.net（老羅的繽紛天地）
;注意事項：如欲轉載，請保持本程序的完整，并注明：
;轉載自“老羅的繽紛天地”（http://laoluoc.yeah.net）
;***********************************************

.386
.model flat, stdcall
option casemap:none

include \masm32\include\windows.inc
include \masm32\include\kernel32.inc
include \masm32\include\user32.inc
includelib \masm32\lib\kernel32.lib
includelib \masm32\lib\user32.lib

DllEntry		proto :HINSTANCE, :DWORD, :DWORD
Base64Encode	proto :DWORD, :DWORD
Base64Decode	proto :DWORD, :DWORD

.data
;Base64 -> ASCII mapping table
base64_alphabet		db	"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="

;ASCII -> Base64 mapping table
base64table			db 43 dup (255)
		 			db 62,255,255,255,63,52,53,54,55,56,57,58,59,60,61,255
					db 255,255,0,255,255,255,0,1,2,3,4,5,6,7,8,9,10,11,12,13
					db 14,15,16,17,18,19,20,21,22,23,24,25,255,255,255,255
					db 255,255,26,27,28,29,30,31,32,33,34,35,36,37,38
					db 39,40,41,42,43,44,45,46,47,48,49,50,51
					db 132 dup (255)

.code
DllEntry	proc	hInst: HINSTANCE, reason: DWORD, reserved1: DWORD
	mov eax, TRUE
	ret
DllEntry	endp


;**********************************************************
;函數功能：進行Base64編碼
;參數：
;	source		 =	傳入的字符串
;	destination	 =	返回的編碼
;**********************************************************
Base64Encode	proc	uses ebx edi esi source:DWORD, destination:DWORD
	LOCAL	sourcelen:DWORD

	invoke lstrlen, source
	mov sourcelen, eax

	mov  esi, source
	mov  edi, destination
@@base64loop:
	xor eax, eax
	.if sourcelen == 1
		lodsb						;source ptr + 1
		mov ecx, 2					;bytes to output = 2
		mov edx, 03D3Dh				;padding = 2 byte
		dec sourcelen				;length - 1
	.elseif sourcelen == 2
		lodsw						;source ptr + 2
		mov ecx, 3					;bytes to output = 3
		mov edx, 03Dh				;padding = 1 byte
		sub sourcelen, 2			;length - 2
	.else
		lodsd
		mov ecx, 4					;bytes to output = 4
		xor edx, edx				;padding = 0 byte
		dec esi						;source ptr + 3 (+4-1)
		sub sourcelen, 3			;length - 3 
	.endif

	xchg al,ah						;flip eax completely
	rol  eax, 16					;can this be done faster
	xchg al,ah

	@@:
	push  eax
	and   eax, 0FC000000h			;get the last 6 high bits
	rol   eax, 6					;rotate them into al
	mov   al,  byte ptr [offset base64_alphabet + eax]		;get encode character
	stosb							;write to destination
	pop   eax
	shl   eax, 6					;shift left 6 bits
	dec   ecx
	jnz   @B						;loop

	cmp   sourcelen, 0
	jnz   @@base64loop				;main loop

	mov   eax, edx					;add padding and null terminate
	stosd

	ret
Base64Encode	endp


;**********************************************************
;函數功能：進行Base64解碼
;參數：
;	source		 =	傳入的編碼
;	destination	 =	返回的字符串
;**********************************************************
Base64Decode	proc	uses ebx edi esi source:DWORD, destination:DWORD
	LOCAL	sourcelen:DWORD

	invoke lstrlen, source
	mov sourcelen, eax
	
	mov    esi, source			;esi <- source
	mov    edi, destination		;edi <- destination
	mov    ecx, sourcelen
	shr    ecx, 2
	cld
	
	;-------------[decoding part]---------------
	
@@outer_loop:
	push   ecx
	mov    ecx, 4
	xor    ebx, ebx
	lodsd
@@inner_loop:
	push   eax
	and    eax, 0ffh
	mov    al, byte ptr [offset base64table + eax]
	cmp    al, 255
	je     @@invalid_char
	shl    ebx, 6
	or     bl, al
	pop    eax
	shr    eax, 8
	dec    ecx
	jnz    @@inner_loop
	mov    eax, ebx
	shl    eax, 8 
	xchg   ah, al
	ror    eax, 16
	xchg   ah, al
	stosd
	dec    edi
	pop    ecx
	dec    ecx
	jnz    @@outer_loop
	xor    eax, eax
	jmp    @@decode_done
	
	;-------------------------------------------
	
@@invalid_char:
	mov    eax, -1
@@decode_done:
	ret
Base64Decode ENDP


end DllEntry
;********************	over	********************
;by LC