Fibonacci sequence: Difference between revisions
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(→{{header|Forth}}: Add version with support for negative indexes) |
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<lang forth>: fib ( n -- fib ) |
<lang forth>: fib ( n -- fib ) |
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0 1 rot 0 ?do over + swap loop drop ;</lang> |
0 1 rot 0 ?do over + swap loop drop ;</lang> |
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Or, for negative-index support: |
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<lang forth>: fib ( n -- Fn ) 0 1 begin |
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rot dup 0 = if drop drop exit then |
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dup 0 > if 1 - rot rot dup rot + |
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else 1 + rot rot over - swap then |
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again ;</lang> |
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Since there are only a fixed and small amount of Fibonacci numbers that fit in a machine word, this FORTH version creates a table of Fibonacci numbers at compile time. It stops compiling numbers when there is arithmetic overflow (the number turns negative, indicating overflow.) |
Since there are only a fixed and small amount of Fibonacci numbers that fit in a machine word, this FORTH version creates a table of Fibonacci numbers at compile time. It stops compiling numbers when there is arithmetic overflow (the number turns negative, indicating overflow.) |
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