From e6e9e2cdce04a08ada4881d53b634fbaf8fa1f0c Mon Sep 17 00:00:00 2001
From: Lumi Pakkanen <lumi.pakkanen@gmail.com>
Date: Tue, 26 Dec 2023 21:37:48 +0200
Subject: [PATCH] Make convergent calculator more sane

---
 src/__tests__/approximation.spec.ts |  6 ++++++
 src/approximation.ts                | 22 +++++++++++++---------
 2 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/src/__tests__/approximation.spec.ts b/src/__tests__/approximation.spec.ts
index 1d4669f..c3e6a4c 100644
--- a/src/__tests__/approximation.spec.ts
+++ b/src/__tests__/approximation.spec.ts
@@ -120,6 +120,12 @@ describe('Convergent calculator', () => {
     expect(semiconvergents[3].equals('10/3')).toBeTruthy();
     expect(semiconvergents[4].equals('13/4')).toBeTruthy();
   });
+
+  it('calculates convergents for 1\\5', () => {
+    expect(() =>
+      getConvergents(1.148698354997035, undefined, 256, true, false)
+    ).not.toThrow();
+  });
 });
 
 describe('Radical approximator', () => {
diff --git a/src/approximation.ts b/src/approximation.ts
index b37970e..a9737f4 100644
--- a/src/approximation.ts
+++ b/src/approximation.ts
@@ -52,17 +52,21 @@ export function getConvergents(
         if (includeNonMonotonic) {
           result.push(convergent);
         } else {
-          // See https://en.wikipedia.org/wiki/Continued_fraction#Semiconvergents
-          // for the origin of this half-rule
           if (2 * i > cfDigit) {
             result.push(convergent);
-          } else if (
-            convergent
-              .sub(value_)
-              .abs()
-              .compare(result[result.length - 1].sub(value_).abs()) < 0
-          ) {
-            result.push(convergent);
+          } else {
+            // See https://en.wikipedia.org/wiki/Continued_fraction#Semiconvergents
+            // for the origin of this half-rule
+            try {
+              const halfRule =
+                convergent
+                  .sub(value_)
+                  .abs()
+                  .compare(result[result.length - 1].sub(value_).abs()) < 0;
+              if (halfRule) {
+                result.push(convergent);
+              }
+            } catch {}
           }
         }
         if (result.length >= maxLength!) {