From e57a1c0335e85959314ce5a8e61b3f08350f6248 Mon Sep 17 00:00:00 2001
From: filifa <filifa.breath652@8alias.com>
Date: Mon, 4 May 2026 22:25:30 -0400
Subject: [PATCH] add ability to sieve custom function

---
 junk/sieves/sieves.html | 11 ++++++++++-
 junk/sieves/sieves.js   | 14 ++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/junk/sieves/sieves.html b/junk/sieves/sieves.html
index 9762914..5664a17 100644
--- a/junk/sieves/sieves.html
+++ b/junk/sieves/sieves.html
@@ -20,6 +20,7 @@
 				<hgroup>
 					<h1>Sieving Multiplicative Functions</h1>
 					<p>Posted <time datetime="2026-04-15">April 15, 2026</time></p>
+					<p>Updated <time datetime="2026-05-04">May 4, 2026</time></p>
 				</hgroup>
 
 				<p>The
@@ -76,8 +77,15 @@
 							<option value="mobius">Mobius</option>
 							<option value="big-omega">Prime omega (with multiplicity)</option>
 							<option value="little-omega">Prime omega (without multiplicity)</option>
+							<option value="custom">Custom</option>
 						</select>
 
+						<label hidden id="custom-function-label" for="custom-function">Custom function definition</label>
+						<textarea hidden spellcheck=false placeholder="return Math.pow(p, k-1) * (p-1);" id="custom-function"></textarea>
+
+						<label hidden id="custom-function-additive-label" for="custom-function-additive">Function is additive</label>
+						<input hidden type="checkbox" id="custom-function-additive" />
+
 						<input type="button" id="enter" value="Enter" />
 					</div>
 
@@ -1125,7 +1133,8 @@ function mobius(p, k) {
 
 					<p>Many multiplicative and additive functions have simple formulas
 					for prime powers, which makes adding a new function to sieve very
-					easy with this approach.</p>
+					easy with this approach. The demo even lets you write your own custom
+					function to sieve - try it out!</p>
 				</section>
 
 				<section>
diff --git a/junk/sieves/sieves.js b/junk/sieves/sieves.js
index d787c0d..1c76431 100644
--- a/junk/sieves/sieves.js
+++ b/junk/sieves/sieves.js
@@ -133,6 +133,14 @@ function sieveMultiples(p, q, l, r, y, sieve, quo, additive) {
 	}
 }
 
+function setCustomFunctionVisibility(e) {
+	const isHidden = e.target.value !== "custom";
+	document.querySelector("#custom-function-label").hidden = isHidden;
+	document.querySelector("#custom-function").hidden = isHidden;
+	document.querySelector("#custom-function-additive-label").hidden = isHidden;
+	document.querySelector("#custom-function-additive").hidden = isHidden;
+}
+
 function getFunc(func) {
 	switch (func.value) {
 		case "num-divisors":
@@ -149,6 +157,11 @@ function getFunc(func) {
 			return [littleOmega, true];
 		case "big-omega":
 			return [bigOmega, true];
+		case "custom":
+			const def = document.querySelector("#custom-function");
+			const isAdditive = document.querySelector("#custom-function-additive");
+			const f = new Function("p", "k", def.value);
+			return [f, isAdditive.checked];
 		default:
 			throw new Error("function not implemented!");
 	}
@@ -219,4 +232,5 @@ function calculate() {
 	result.appendChild(table);
 }
 
+document.querySelector("#function").addEventListener("change", (e) => setCustomFunctionVisibility(e))
 document.querySelector("#enter").addEventListener("click", () => calculate())