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sumsq.cal
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1995-07-17
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869b
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45 lines
/*
* Copyright (c) 1993 David I. Bell
* Permission is granted to use, distribute, or modify this source,
* provided that this copyright notice remains intact.
*
* Determine the unique two positive integers whose squares sum to the
* specified prime. This is always possible for all primes of the form
* 4N+1, and always impossible for primes of the form 4N-1.
*/
define ss(p)
{
local a, b, i, p4;
if (p == 2) {
print "1^2 + 1^2 = 2";
return;
}
if ((p % 4) != 1) {
print p, "is not of the form 4N+1";
return;
}
if (!ptest(p, min(p-2, 10))) {
print p, "is not a prime";
return;
}
p4 = (p - 1) / 4;
i = 2;
do {
a = pmod(i++, p4, p);
} while ((a^2 % p) == 1);
b = p;
while (b^2 > p) {
i = b % a;
b = a;
a = i;
}
print a : "^2 +" , b : "^2 =" , a^2 + b^2;
}
global lib_debug;
if (lib_debug >= 0) {
print "ss(p) defined";
}