base64.asm

WIN 32 汇编编写的BASE64 的编码和解码

;***********************************************
;程序名称：演示Base64编码/解码原理
;作者：罗聪
;日期：2002-9-14
;出处：http://laoluoc.yeah.net（老罗的缤纷天地）
;注意事项：如欲转载，请保持本程序的完整，并注明：
;转载自“老罗的缤纷天地”（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


;**********************************************************
;函数功能：进行Base64编码
;参数：
;    source          =    传入的字符串
;    destination     =    返回的编码
;**********************************************************
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


;**********************************************************
;函数功能：进行Base64解码
;参数：
;    source          =    传入的编码
;    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