Encodes and decodes base64 strings

                                    ` This code was downloaded from The Game Creators
                                    ` It is reproduced here with full permission
                                    ` http://www.thegamecreators.com
                                    
                                    REM *************************************************
REM * Original Author: Randy Charles Morin
REM * Author's Website: http://www.kbcafe.com (2006)
REM *
REM * Ported from C++ to AGK
REM *
REM * Converted By: Phaelax
REM * Website: http://zimnox.com
REM *************************************************


function encode64$(encode as string)

    value$ = ""
    length = len(encode)

    for i = 1 to length step 3

        b1 = asc(mid(encode, i, 1))
        b2 = 0
        b3 = 0



        if (i+1 <= length) then b2 = asc(mid(encode, i+1, 1))
        if (i+2 <= length) then b3 = asc(mid(encode, i+2, 1))

        b4 = b1 >> 2
        b5 = ((b1&&0x3)<<4) || (b2>>4)
        b6 = ((b2&&0xf)<<2) || (b3>>6)
        b7 = b3 && 0x3f

        value$ = value$ + encodeByte$(b4)
        value$ = value$ + encodeByte$(b5)

        if i+1 <= length
            value$ = value$ + encodeByte$(b6)
        else
            value$ = value$ + "="
        endif

        if i+2 <= length
            value$ = value$ + encodeByte$(b7)
        else
            value$ = value$ + "="
        endif

        if mod(i, 76) = 0 then value$ = value$ + chr(13)+chr(10)

    next i

endfunction value$



function decode64$(decode as string)
    value$ = ""
    temp$  = ""

    if isBase64(decode) = 0 then exitfunction ""

    length = len(decode)

    for i = 1 to length step 4

        c1$ = mid(decode, i, 1)
        c2$ = "A"
        c3$ = "A"
        c4$ = "A"

        if i+1 <= length then c2$ = mid(decode, i+1, 1)
        if i+2 <= length then c3$ = mid(decode, i+2, 1)
        if i+3 <= length then c4$ = mid(decode, i+3, 1)

        b1 = decodeChar(c1$)
        b2 = decodeChar(c2$)
        b3 = decodeChar(c3$)
        b4 = decodeChar(c4$)

        value$ = value$ + chr(b1<<2 || b2>>4)

        if c3$ <> "=" then value$ = value$ + chr(((b2&&0xf)<<4) || (b3>>2))
        if c4$ <> "=" then value$ = value$ + chr(((b3&&0x3)<<6) || b4)

    next i

endfunction value$



function isBase64(check as string)
    c as string
    for i = 1 to len(check)
        thing = 0
        c = mid(check, i, 1)
        if c >= "A" and c <= "Z" then thing = 1
        if c >= "a" and c <= "z" then thing = 1
        if c >= "0" and c <= "9" then thing = 1
        if c = "+" then thing = 1
        if c = "/" then thing = 1
        if c = "=" then thing = 1
        if thing = 0 then exitfunction 0
    next i
endfunction 1


function encodeByte$(byte)
    if byte < 26 then exitfunction chr(asc("A")+ byte)
    if byte < 52 then exitfunction chr(asc("a")+(byte-26))
    if byte < 62 then exitfunction chr(asc("0")+(byte-52))
    if byte = 62 then exitfunction "+"
endfunction "/"


function decodeChar(c as string)
    if c >= "A" and c <= "Z"
        v = asc(c)-65
        exitfunction v
    endif
    if c >= "a" and c <= "z"
        v = asc(c)-97+26
        exitfunction v
    endif
    if c >= "0" and c <= "9"
        v = asc(c)-48+52
        exitfunction v
    endif
    if c =  "+" then exitfunction 62
endfunction 63