Ethiopian multiplication: Difference between revisions
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=={{header|Forth}}== |
=={{header|Forth}}== |
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Halve and double are standard words, spelled '''2/''' and '''2*''' respectively. |
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{{incorrect|Forth|No functions/subroutines defined to perform the three actions as specified in the task description}} |
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<lang forth>: |
<lang forth>: even? ( n -- ? ) 1 and 0= ; |
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: e* ( x y -- x*y ) |
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dup 0= if nip exit then |
dup 0= if nip exit then |
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over 2* over 2/ recurse |
over 2* over 2/ recurse |
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swap |
swap even? if nip else + then ;</lang> |
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The author of Forth, Chuck Moore, designed a similar primitive into his MISC Forth microprocessors. The '''+*''' instruction is a multiply step: it adds S to T if A is odd, then shifts both A and T right one. The idea is that you only need to perform as many of these multiply steps as you have significant bits in the operand. (See his [http://www.colorforth.com/inst.htm core instruction set] for details.) |
The author of Forth, Chuck Moore, designed a similar primitive into his MISC Forth microprocessors. The '''+*''' instruction is a multiply step: it adds S to T if A is odd, then shifts both A and T right one. The idea is that you only need to perform as many of these multiply steps as you have significant bits in the operand. (See his [http://www.colorforth.com/inst.htm core instruction set] for details.) |
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