Data commit

Task/Legendre-prime-counting-function/JavaScript/legendre-prime-counting-function-1.js

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