63 lines
1.2 KiB
Forth
63 lines
1.2 KiB
Forth
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\ primes.4th
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\
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\ Example code for kForth
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\ Copyright (c) 1998 Creative Consulting for Research and Education
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\
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\ Test for a prime number. Return the largest divisor (< n )
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\ and a flag indicating whether the number is prime or not.
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: ?prime ( n -- m flag | is n a prime number? )
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\ if flag is false (0), m is the largest divisor of n
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abs
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dup 3 > \ is n > 3 ?
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if
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abs
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dup 2 /mod
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swap 0=
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if \ is n divisible by 2 ?
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nip false
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else
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1- \ check for divisibility starting
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begin \ with n/2 - 1 and counting down
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2dup mod
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over 1 >
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and
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while
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1-
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repeat
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nip
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dup 1 <=
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then
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else
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dup 1 > IF drop 1 true ELSE false THEN
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then
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;
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: test_prime ( n -- | test for prime number and display result )
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?prime
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if
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." is a prime number" drop
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else
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." is NOT prime. Its largest divisor is " .
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then
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cr
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;
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: list_primes ( n -- | list all the prime numbers from 2 to n )
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abs
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dup 0>
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if
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1+ 2 do
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i ?prime
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if
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i . cr
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then
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drop
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loop
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else
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drop
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then
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;
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