32 lines
1.0 KiB
JavaScript
32 lines
1.0 KiB
JavaScript
"use strict";
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function countPrimesTo(lmt) {
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if (lmt < 3) { if (lmt < 2) return 0; else return 1; }
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const sqrtlmt = Math.sqrt(lmt) >>> 0;
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const oprms = function() {
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const mxndx = (sqrtlmt - 3) >>> 1;
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const arr = new Float64Array(mxndx + 1);
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for (let i = 0 >>> 0; i <= mxndx; ++i) arr[i] = (i + i + 3) >>> 0;
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let bp = 3 >>> 0;
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while (true) {
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let i = (bp - 3) >>> 1; let sqri = ((i + i) * (i + 3) + 3) >>> 0;
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if (sqri > mxndx) break;
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if (arr[i] != 0) for (; sqri <= mxndx; sqri += bp) arr[sqri] = 0;
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bp += 2;
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}
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return arr.filter(v => v != 0);
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}();
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function phi(x, a) {
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if (a <= 0) return x - Math.trunc(x / 2);
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const na = (a - 1) >>> 0; const p = oprms[na];
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if (x <= p) return 1;
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return phi(x, na) - phi(Math.trunc(x / p), na);
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}
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return phi(lmt, oprms.length) + oprms.length;
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}
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const start = Date.now();
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for (let i = 0; i <= 9; ++i) console.log(`π(10**${i}) =`, countPrimesTo(10**i));
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const elpsd = Date.now() - start;
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console.log("This took", elpsd, "milliseconds.")
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