中国DOS联盟

@echo off

::::::::Base64 Decode {s11ss 2007-12-3}::::::::

setlocal enabledelayedexpansion

:GetEs
echo 请输入要转换的base64编码：
set/p es=

if "%es%"=="" goto GetEs
echo 转换中...

set "base64=ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="
set/a i=0
:base64-hex
set "o=!es:~%i%,1!"
if not "%o%" equ "" (call :b64-h1by1) else (goto :hex-hex2)
set/a i+=1
goto :base64-hex

:hex-hex2
if not defined hex goto :hex2-str
for /l %%a in (1,1,4) do (
        set/a "n=2*(%%a-1)"
        call set x=%%hex:~!n!,2%%
        set "ec%%a=0x!x!"
        if "!x!" equ "40" (set ec%%a=0& set f%%a=0)        
)
set hex=%hex:~8%
set/a c1=%ec1%"<<"2"|"%ec2%">>"4
set/a c2=%ec2%"<<"4"|"%ec3%">>"2
set/a c3=%ec3%"<<"6"|"%ec4%
for /l %%a in (1,1,3) do (
        set/a c%%a=!c%%a!"&"255
        call :dec-hex !c%%a!
)
if "%f3%" equ "0" set "c2="
if "%f4%" equ "0" set "c3="
for /l %%a in (1,1,3) do call set "hex2=%%hex2%%%%r!c%%a!%%"
goto :hex-hex2

:hex2-str
set vbs=%tmp%\tt.vbs
if exist %vbs% goto :runVBS
        :createVBS
set t=^>^>%vbs% echo
%t%h=wscript.arguments(0)
%t%s=""
%t%for i=1 to len(h) step 2
%t%        a=cint("&h"^&mid(h,i,2))
%t%        if a^>160 then
%t%                a=cint("&h"^&mid(h,i,4))
%t%                i=i+2
%t%        end if
%t%        s=s^&chr(a)        
%t%next  
%t%wscript.stdout.write(s)
        :runVBS
for /f "delims=" %%a in ('cscript//nologo %vbs% %hex2%') do set "s=%%a"

:print
echo.
echo 转换结果（不包括最外边的一对引号）：
echo."%s%"
pause
goto :eof











:b64-h1by1
for /l %%a in (0,1,64) do (
        if "!base64:~%%a,1!" equ "%o%" (
                call :dec-hex %%a
                set hex=!hex!!r%%a!
                goto :eof
        )
)
goto :eof

:dec-hex
set "r%1="
set "h=0123456789ABCDEF"
set/a q=%1
        :1c
        set/a r=%q%%%16
        set/a q=%q%/16
        call set r=%%h:~%r%,1%%
        set r%1=%r%!r%1!
if not %q% equ 0 goto :1c
if %1 leq 0xf set r%1=0!r%1!