From 98ec02ac243902c406df98539ff6b7f6563db42f Mon Sep 17 00:00:00 2001
From: Davis Rens <166565828+davrens101@users.noreply.github.com>
Date: Sun, 1 Nov 2026 18:38:43 -0800
Subject: [PATCH 1/2] Prevent double-precision underflow in findEmpties for
 deep empty regions (#8108)

---
 draftlogs/pending_fix.md           |  1 +
 src/traces/heatmap/find_empties.js | 12 +++++++++---
 test/jasmine/tests/heatmap_test.js | 27 +++++++++++++++++++++++++++
 3 files changed, 37 insertions(+), 3 deletions(-)
 create mode 100644 draftlogs/pending_fix.md

diff --git a/draftlogs/pending_fix.md b/draftlogs/pending_fix.md
new file mode 100644
index 00000000000..57c73b28cb0
--- /dev/null
+++ b/draftlogs/pending_fix.md
@@ -0,0 +1 @@
+- Prevent double-precision underflow in `findEmpties` for deep empty (NaN) regions [[#8108](https://github.com/plotly/plotly.js/issues/8108)]
diff --git a/src/traces/heatmap/find_empties.js b/src/traces/heatmap/find_empties.js
index 88c75894fcd..406759f3fc2 100644
--- a/src/traces/heatmap/find_empties.js
+++ b/src/traces/heatmap/find_empties.js
@@ -23,6 +23,7 @@ module.exports = function findEmpties(z) {
     var thisPt;
     var p;
     var neighborCount;
+    var neighborSum;
     var newNeighborHash;
     var foundNewNeighbors;
 
@@ -67,12 +68,17 @@ module.exports = function findEmpties(z) {
             i = thisPt[0];
             j = thisPt[1];
 
-            neighborCount = ((neighborHash[[i - 1, j]] || blank)[2] +
+            neighborSum = (neighborHash[[i - 1, j]] || blank)[2] +
                 (neighborHash[[i + 1, j]] || blank)[2] +
                 (neighborHash[[i, j - 1]] || blank)[2] +
-                (neighborHash[[i, j + 1]] || blank)[2]) / 20;
+                (neighborHash[[i, j + 1]] || blank)[2];
+
+            if(neighborSum) {
+                neighborCount = neighborSum / 20;
+                // neighborSum / 20 can underflow to 0 in float64 when deep empty regions decay
+                // past ~249 layers, but this cell does have neighbours: keep a strictly positive weight
+                if(!neighborCount) neighborCount = Number.MIN_VALUE;
 
-            if(neighborCount) {
                 newNeighborHash[thisPt] = [i, j, neighborCount];
                 noNeighborList.splice(p, 1);
                 foundNewNeighbors = true;
diff --git a/test/jasmine/tests/heatmap_test.js b/test/jasmine/tests/heatmap_test.js
index ceb527f4132..557549629ff 100644
--- a/test/jasmine/tests/heatmap_test.js
+++ b/test/jasmine/tests/heatmap_test.js
@@ -4,6 +4,7 @@ var Lib = require('../../../src/lib');
 var setConvert = require('../../../src/plots/cartesian/set_convert');
 
 var convertColumnXYZ = require('../../../src/traces/heatmap/convert_column_xyz');
+var findEmpties = require('../../../src/traces/heatmap/find_empties');
 var Heatmap = require('../../../src/traces/heatmap');
 
 var d3Select = require('../../strict-d3').select;
@@ -1115,3 +1116,29 @@ describe('heatmap hover', function() {
         });
     });
 });
+
+describe('findEmpties', function() {
+    'use strict';
+
+    it('should fill deep empty regions without floating-point underflow (#8108)', function() {
+        // 5 rows, column 0 is defined, columns 1..250 are undefined (empty).
+        // Depth of 250 causes geometric weight decay (1/20)^249 to underflow double precision.
+        var z = [];
+        var r;
+        var i;
+        var j;
+        var nanCount = 250;
+        for(i = 0; i < 5; i++) {
+            r = [1];
+            for(j = 0; j < nanCount; j++) r.push(undefined);
+            z.push(r);
+        }
+
+        var empties;
+        expect(function() {
+            empties = findEmpties(z);
+        }).not.toThrow();
+
+        expect(empties.length).toBe(5 * nanCount);
+    });
+});

From 7374ddd386442132122df271e8b330e5ad788ae5 Mon Sep 17 00:00:00 2001
From: Davis Rens <166565828+davrens101@users.noreply.github.com>
Date: Sun, 1 Nov 2026 18:39:53 -0800
Subject: [PATCH 2/2] Link PR #8162 in draftlog

---
 draftlogs/8162_fix.md    | 1 +
 draftlogs/pending_fix.md | 1 -
 2 files changed, 1 insertion(+), 1 deletion(-)
 create mode 100644 draftlogs/8162_fix.md
 delete mode 100644 draftlogs/pending_fix.md

diff --git a/draftlogs/8162_fix.md b/draftlogs/8162_fix.md
new file mode 100644
index 00000000000..533a28c2830
--- /dev/null
+++ b/draftlogs/8162_fix.md
@@ -0,0 +1 @@
+- Prevent double-precision underflow in `findEmpties` for deep empty (NaN) regions [[#8162](https://github.com/plotly/plotly.js/pull/8162)]
diff --git a/draftlogs/pending_fix.md b/draftlogs/pending_fix.md
deleted file mode 100644
index 57c73b28cb0..00000000000
--- a/draftlogs/pending_fix.md
+++ /dev/null
@@ -1 +0,0 @@
-- Prevent double-precision underflow in `findEmpties` for deep empty (NaN) regions [[#8108](https://github.com/plotly/plotly.js/issues/8108)]