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BASE32では5バイト40bitを5bitずつ8つに分け32進文字列に変換します。
文字数が5の倍数ではない時"="で埋めます。
5バイトを8文字に変換するので増大率は8/5倍になります。
https://en.wikipedia.org/wiki/Base32
OPTION CHARACTER BYTE
DO
READ IF MISSING THEN EXIT DO:A$
LET S$=ENCODEBASE32$(A$)
PRINT "原文 :";A$
PRINT "ENCODE:";S$
PRINT "DECODE:";DECODEBASE32$(S$)
PRINT
LOOP
DATA A
DATA AB
DATA ABC
DATA ABCD
DATA ABCDE
DATA ABCDEFGHIJKLMNOPQRSTUVWXYZ
DATA 0123456789
DATA 十進BASIC
END
EXTERNAL FUNCTION ENCODEBASE32$(A$)
OPTION CHARACTER BYTE
LET S$="ABCDEFGHIJKLMNOPQRSTUVWXYZ234567"
LET L=MOD(LEN(A$),5)
FOR I=0 TO INT(LEN(A$)/5)-1
LET D$=A$(5*I+1:5*I+5)
LET N=ORD(D$(1:1))*256^4+ORD(D$(2:2))*256^3+ORD(D$(3:3))*256^2+ORD(D$(4:4))*256+ORD(D$(5:5))
LET N1=MOD(INT(N/32^7),32)+1
LET N2=MOD(INT(N/32^6),32)+1
LET N3=MOD(INT(N/32^5),32)+1
LET N4=MOD(INT(N/32^4),32)+1
LET N5=MOD(INT(N/32^3),32)+1
LET N6=MOD(INT(N/32^2),32)+1
LET N7=MOD(INT(N/32),32)+1
LET N8=MOD(N,32)+1
LET ENC$=ENC$&S$(N1:N1)&S$(N2:N2)&S$(N3:N3)&S$(N4:N4)&S$(N5:N5)&S$(N6:N6)&S$(N7:N7)&S$(N8:N8)
NEXT I
LET D$=A$(5*I+1:LEN(A$))
SELECT CASE L
CASE 0
CASE 4
!'4byte 32bit 12345 67812 34567 81234 56781 23456 78000 8倍して5bitずつ*7つ
LET N=ORD(D$(1:1))*256^3+ORD(D$(2:2))*256^2+ORD(D$(3:3))*256+ORD(D$(4:4))
LET N=N*8
LET N1=MOD(INT(N/32^6),32)+1
LET N2=MOD(INT(N/32^5),32)+1
LET N3=MOD(INT(N/32^4),32)+1
LET N4=MOD(INT(N/32^3),32)+1
LET N5=MOD(INT(N/32^2),32)+1
LET N6=MOD(INT(N/32),32)+1
LET N7=MOD(N,32)+1
LET ENC$=ENC$&S$(N1:N1)&S$(N2:N2)&S$(N3:N3)&S$(N4:N4)&S$(N5:N5)&S$(N6:N6)&S$(N7:N7)&"="
CASE 3
!'3byte 24bit 12345 67812 34567 81234 56780 2倍して5bitずつ*5つ
LET N=ORD(D$(1:1))*256^2+ORD(D$(2:2))*256+ORD(D$(3:3))
LET N=N*2
LET N1=MOD(INT(N/32^4),32)+1
LET N2=MOD(INT(N/32^3),32)+1
LET N3=MOD(INT(N/32^2),32)+1
LET N4=MOD(INT(N/32),32)+1
LET N5=MOD(N,32)+1
LET ENC$=ENC$&S$(N1:N1)&S$(N2:N2)&S$(N3:N3)&S$(N4:N4)&S$(N5:N5)&"==="
CASE 2
!'2byte 16bit 12345 67812 34567 80000 16倍して5bitずつ*4つ
LET N=ORD(D$(1:1))*256+ORD(D$(2:2))
LET N=N*16
LET N1=MOD(INT(N/32^3),32)+1
LET N2=MOD(INT(N/32^2),32)+1
LET N3=MOD(INT(N/32),32)+1
LET N4=MOD(N,32)+1
LET ENC$=ENC$&S$(N1:N1)&S$(N2:N2)&S$(N3:N3)&S$(N4:N4)&"===="
CASE 1
!'1byte 8bit 12345 67800 4倍して5bitずつ*2つ
LET N=ORD(D$)
LET N=N*4
LET N1=MOD(INT(N/32),32)+1
LET N2=MOD(N,32)+1
LET ENC$=ENC$&S$(N1:N1)&S$(N2:N2)&"======"
END SELECT
LET ENCODEBASE32$=ENC$
END FUNCTION
EXTERNAL FUNCTION DECODEBASE32$(M$)
OPTION CHARACTER BYTE
LET A$="ABCDEFGHIJKLMNOPQRSTUVWXYZ234567"
FOR I=0 TO LEN(M$)/8-1
LET L$=M$(8*I+1:8*I+8)
IF RIGHT$(L$,6)="======" THEN
LET N1=POS(A$,L$(1:1))-1
LET N2=POS(A$,L$(2:2))-1
LET N=N1*32+N2
LET N=N/4
LET DEC$=DEC$&CHR$(MOD(N,256))
ELSEIF RIGHT$(L$,4)="====" THEN
LET N1=POS(A$,L$(1:1))-1
LET N2=POS(A$,L$(2:2))-1
LET N3=POS(A$,L$(3:3))-1
LET N4=POS(A$,L$(4:4))-1
LET N=N1*32^3+N2*32^2+N3*32+N4
LET N=N/16
LET DEC$=DEC$&CHR$(MOD(INT(N/256),256))&CHR$(MOD(N,256))
ELSEIF RIGHT$(L$,3)="===" THEN
LET N1=POS(A$,L$(1:1))-1
LET N2=POS(A$,L$(2:2))-1
LET N3=POS(A$,L$(3:3))-1
LET N4=POS(A$,L$(4:4))-1
LET N5=POS(A$,L$(5:5))-1
LET N=N1*32^4+N2*32^3+N3*32^2+N4*32+N5
LET N=N/2
LET DEC$=DEC$&CHR$(MOD(INT(N/256^2),256))&CHR$(MOD(INT(N/256),256))&CHR$(MOD(N,256))
ELSEIF RIGHT$(L$,1)="=" THEN
LET N1=POS(A$,L$(1:1))-1
LET N2=POS(A$,L$(2:2))-1
LET N3=POS(A$,L$(3:3))-1
LET N4=POS(A$,L$(4:4))-1
LET N5=POS(A$,L$(5:5))-1
LET N6=POS(A$,L$(6:6))-1
LET N7=POS(A$,L$(7:7))-1
LET N=N1*32^6+N2*32^5+N3*32^4+N4*32^3+N5*32^2+N6*32+N7
LET N=N/8
LET DEC$=DEC$&CHR$(MOD(INT(N/256^3),256))&CHR$(MOD(INT(N/256^2),256))&CHR$(MOD(INT(N/256),256))&CHR$(MOD(N,256))
ELSE
LET N1=POS(A$,L$(1:1))-1
LET N2=POS(A$,L$(2:2))-1
LET N3=POS(A$,L$(3:3))-1
LET N4=POS(A$,L$(4:4))-1
LET N5=POS(A$,L$(5:5))-1
LET N6=POS(A$,L$(6:6))-1
LET N7=POS(A$,L$(7:7))-1
LET N8=POS(A$,L$(8:8))-1
LET N=N1*32^7+N2*32^6+N3*32^5+N4*32^4+N5*32^3+N6*32^2+N7*32+N8
LET DEC$=DEC$&CHR$(MOD(INT(N/256^4),256))&CHR$(MOD(INT(N/256^3),256))&CHR$(MOD(INT(N/256^2),256))&CHR$(MOD(INT(N/256),256))&CHR$(MOD(N,256))
END IF
NEXT I
LET DECODEBASE32$=DEC$
END FUNCTION
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