#1✎ 24DevinF06Intermediate ProgrammerI can make programs, but I still have trouble here and there. Programming StrengthVideo GamesI like to play video games!HobbiesI need some help making a Base64 Decoder
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Edited
by DevinF06
#2✎ 166512Me21Head AdminThird YearMy account is over 3 years oldWebsiteSyntax HighlighterReceived for creating the code syntax highlighter on SBSNight PersonI like the quiet night and sleep late.Express YourselfVAR BASE64$ = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
'Converting a base 64 character in to a number from 0 to 63:
'(This isn't the most efficient method but it's the simplest)
DEF READ_B64_DIGIT(D$)
VAR D=INSTR(BASE64$,D$[I])
IF D<0 THEN
PRINT "Illegal character found"
BEEP
STOP
ENDIF
RETURN D
END
DEF DECODE_B64(B64$)
IF LEN(B64$) MOD 4 THEN
PRINT "Length must be a multiple of 4"
BEEP
STOP
ENDIF
DIM RET[0]
VAR TEMP,TEMP_SIZE
VAR I
FOR I=0 TO LEN(B64$)-1
IF B64$[I]=="=" THEN BREAK
TEMP=TEMP<<6 OR READ_B64_DIGIT(B64$[I])
INC TEMP_SIZE,6
IF TEMP_SIZE>=8 THEN
DEC TEMP_SIZE,8
PUSH RET,TEMP>>TEMP_SIZE AND 255
ENDIF
NEXT
RETURN RET
END
Basically the way this works is that each base 64 character contains 6 bits of information, and you need to output a list of 8-bit values.
So it reads the base 64 string, and keeps track of the 6 bits from each character. When it has at least 8 bits, it takes the oldest 8 bits and adds them to the output array.
Posted
Edited
by 12Me21
#3✎ 98seggiepantsI am too slow. Do you want my example, it has a encoder and a decoder? Well, just in case and so my effort wasn't in vain, here it is. Please excuse any type-os as I manually retyped this in. If you wanted it to work with arrays instead, it shouldn't be too hard to adapt. So, what do you need Base64 for? I hope I didn't just do your homework.
OPTION STRICT
VAR BASE64_INDEX$ = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
VAR TEST$ = "Hello world! This is a test of the Base64 Encoder / Decoder." + CHR$(10) + "I used " + CHR$(34) + "[url=http://en.wikipedia.org/wiki/Base_64"]http://en.wikipedia.org/wiki/Base_64"[/url]; + CHR$(34) + " as a implementation reference. It will encode / decode string."
VAR RESULT$ = ""
RESULT$ = ENCODE_BASE64(TEST$)
PRINT RESULT$
RESULT$ = DECODE_BASE64(RESULT$)
PRINT RESULT$
END
DEF ENCODE_BASE64(VALUE$)
VAR MAX_WIDTH = 40
VAR LINE_LEN = 0
VAR MSG_LEN = LEN(VALUE$)
VAR RET$ = ""
VAR I, J, IDX
VAR TEMP$, WORK$ = ""
FOR 1 = 0 TO MSG_LEN - 1 STEP 3
WORK$ = WORK$ + BIN$(ASC(MID$(VALUE$, I, 1)), 8)
IF I + 1 < MSG_LEN THEN
WORK$ = WORK$ + BIN$(ASC(MID$(VALUE$, I + 1, 1)), 8)
ENDIF
IF I + 2 < MSG_LEN THEN
WORK$ = WORK$ + BIN$(ASC(MID$(VALUE$, I + 2, 1)), 8)
ENDIF
FOR J = 0 TO 3
IF LEN(WORK$) >= 6 THEN
TEMP$ = LEFT$(WORK$, 6)
WORK$ = MID$(WORK$, 6, LEN(WORK$) - 6)
IDX = VAL("&B" + TEMP$)
RET$ = RET$ + MID$(BASE64_INDEX$, IDX, 1)
ELSEIF LEN(WORKI$) >= 1 THEN
TEMP$ = LEFT$(WORK$ + "000000", 6)
WORK$ = ""
IDX = VAL("&B" + TEMP$)
RET$ = RET$ + MID$(BASE64_INDEX$, IDX, 1)
ELSE
RET$ = RET$ + "="
ENDIF
LINE_LEN = LINE_LEN + 1
IF LINE_LEN >= MAX_WIDTH THEN
LINE_LEN = 0
RET$ = RET$ + CHR$(10) 'Enter key
ENDIF
NEXT J
NEXT i
RETURN RET$
END
DEF DECODE_BASE64(VALUE$)
VAR I, J, CH$, RET$ = "", WORK$ = ""
VAR TEMP$, MAX_LEN
IF RIGHT$(VALUE$, 2) = "==" THEN
MAX_LEN = LEN(VALUE$) - 2
IF RIGHT$(VALUE$, 1) = "=" THEN
MAX_LEN = LEN(VALUE$) - 1
ELSE
MAX_LEN = LEN(VALUE$)
ENDIF
FOR I = 0 TO MAX_LEN - 1
CH$ = MID$(VALUE$, I, 1)
J = INSTR(BASE64_INDEX$, CH$)
IF J >= 0 THEN
WORK$ = WORK$ + BIN$(J, 6)
ENDIF
WHILE LEN(WORK$) >= 8
TEMP$ = LEFT$(WORK$, 8)
WORK$ = MID$(WORK$, 8, LEN(WORK$) - 8)
RET$ = RET$ + CHR$(VAL("&B" + TEMP$))
WEND
NEXT i
RETURN RET$
END
Again like the comment at the top of the code says, wikipedia is your friend. https://en.wikipedia.org/wiki/Base_64
Posted
#4✎ 24DevinF06Intermediate ProgrammerI can make programs, but I still have trouble here and there. Programming StrengthVideo GamesI like to play video games!HobbiesThe encoder wasn't a problem, I just indexed the characters ("ABCDEF..."[VAL("&B"+...)])
Anyway, I now have an idea to make my Base64 decoder actually work
EDIT: I had to fix some things, but now it's done
Posted
Edited
by DevinF06
