Decode a base64 string in FoxPro

base64.prg

FUNCTION DECSTR64
PARAMETERS S
    LOCAL i,j,j,k,q,ch,s2,buf,tmpc
    tmpc = 0
    j = 0
    buf = 0
    s2 = ''
    k = LEN(s)
    FOR i = 1 TO k
        ch = ASC(SUBSTR(s,i,1))
        q = IIF((ch >= 97 AND ch <=122),25+ch-96,IIF((ch >= 65 AND ch <=90),ch-65,;
            IIF((ch >= 48 AND ch <=57),ch+4,IIF(ch = 47,63,IIF(ch=43,62,-1)))))
        IF q < 0 THEN
            RETURN IIF(ch = 61,s2,'')
        ENDIF
        buf = BITOR(BITLSHIFT(buf,6),q)
        j = j + 6
        IF j >= 8 THEN
            j = j - 8
            tmpc = CHR(BITAND(BITRSHIFT(buf,j),255))
            buf = BITAND(buf,BITLSHIFT(1,j) -1)
            s2 = s2 + tmpc
        ENDIF
    ENDFOR
    RETURN s2
ENDFUNC