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45 lines
896 B
Plaintext
45 lines
896 B
Plaintext
/*
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* Here is an iterative method of finding the number of primes less than
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* or equal to a given number. This method is from "Computer Recreations"
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* June 1996 issue of Scientific American.
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*
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* NOTE: For reasonable values of x, the builtin function pix(x) is
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* much faster. This code is provided because the method
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* is interesting.
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*/
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define pi_of_x(x)
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{
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local An; /* A(n) */
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local An1; /* A(n-1) */
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local An2; /* A(n-2) */
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local An3; /* A(n-3) */
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local primes; /* number of primes found */
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local n; /* loop counter */
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/*
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* setup
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*/
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An1 = 2;
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An2 = 0;
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An3 = 3;
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primes = 1;
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/*
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* main A(n+1)=A(n-1)+A(n-2) sequence loop
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*/
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for (n = 3; n < x; ++n) {
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An = An2 + An3;
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An3 = An2;
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An2 = An1;
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An1 = An;
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if (An % n == 0)
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++primes;
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}
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return primes;
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}
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if (config("lib_debug") >= 0) {
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print "pi_of_x(x) defined";
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}
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