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30 lines
2.2 KiB
Brainfuck
30 lines
2.2 KiB
Brainfuck
# ROT13 cipher
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-,+[ Read first character and start outer character reading loop
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-[ Skip forward if character is 0
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>>++++[>++++++++<-] Set up divisor (32) for division loop
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(MEMORY LAYOUT: dividend copy remainder divisor quotient zero zero)
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<+<-[ Set up dividend (x minus 1) and enter division loop
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>+>+>-[>>>] Increase copy and remainder / reduce divisor / Normal case: skip forward
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<[[>+<-]>>+>] Special case: move remainder back to divisor and increase quotient
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<<<<<- Decrement dividend
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] End division loop
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]>>>[-]+ End skip loop; zero former divisor and reuse space for a flag
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>--[-[<->+++[-]]]<[ Zero that flag unless quotient was 2 or 3; zero quotient; check flag
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++++++++++++<[ If flag then set up divisor (13) for second division loop
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(MEMORY LAYOUT: zero copy dividend divisor remainder quotient zero zero)
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>-[>+>>] Reduce divisor; Normal case: increase remainder
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>[+[<+>-]>+>>] Special case: increase remainder / move it back to divisor / increase quotient
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<<<<<- Decrease dividend
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] End division loop
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>>[<+>-] Add remainder back to divisor to get a useful 13
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>[ Skip forward if quotient was 0
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-[ Decrement quotient and skip forward if quotient was 1
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-<<[-]>> Zero quotient and divisor if quotient was 2
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]<<[<<->>-]>> Zero divisor and subtract 13 from copy if quotient was 1
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]<<[<<+>>-] Zero divisor and add 13 to copy if quotient was 0
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] End outer skip loop (jump to here if ((character minus 1)/32) was not 2 or 3)
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<[-] Clear remainder from first division if second division was skipped
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<.[-] Output ROT13ed character from copy and clear it
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<-,+ Read next character
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] End character reading loop |