48 lines
1.2 KiB
C
48 lines
1.2 KiB
C
#include <stdio.h>
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#include <stdlib.h>
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#include <stdint.h>
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/* should be 64-bit integers if going over 1 billion */
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typedef unsigned long xint;
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#define FMT "%lu"
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xint total, prim, max_peri;
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xint U[][9] = {{ 1, -2, 2, 2, -1, 2, 2, -2, 3},
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{ 1, 2, 2, 2, 1, 2, 2, 2, 3},
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{-1, 2, 2, -2, 1, 2, -2, 2, 3}};
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void new_tri(xint in[])
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{
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int i;
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xint t[3], p = in[0] + in[1] + in[2];
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if (p > max_peri) return;
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prim ++;
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/* for every primitive triangle, its multiples would be right-angled too;
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* count them up to the max perimeter */
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total += max_peri / p;
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/* recursively produce next tier by multiplying the matrices */
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for (i = 0; i < 3; i++) {
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t[0] = U[i][0] * in[0] + U[i][1] * in[1] + U[i][2] * in[2];
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t[1] = U[i][3] * in[0] + U[i][4] * in[1] + U[i][5] * in[2];
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t[2] = U[i][6] * in[0] + U[i][7] * in[1] + U[i][8] * in[2];
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new_tri(t);
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}
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}
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int main()
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{
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xint seed[3] = {3, 4, 5};
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for (max_peri = 10; max_peri <= 100000000; max_peri *= 10) {
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total = prim = 0;
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new_tri(seed);
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printf( "Up to "FMT": "FMT" triples, "FMT" primitives.\n",
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max_peri, total, prim);
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}
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return 0;
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}
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