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Prevent double-precision underflow in findEmpties for deep empty regions (#8108) #8162

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Prevent double-precision underflow in findEmpties for deep empty regions (#8108) #8162

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Prevent double-precision underflow in findEmpties for deep empty regi…
davrens101 Nov 2, 2026
7374ddd
Link PR #8162 in draftlog
davrens101 Nov 2, 2026
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1 change: 1 addition & 0 deletions draftlogs/8162_fix.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
- Prevent double-precision underflow in `findEmpties` for deep empty (NaN) regions [[#8162](https://github.com/plotly/plotly.js/pull/8162)]
12 changes: 9 additions & 3 deletions src/traces/heatmap/find_empties.js
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Expand Up @@ -23,6 +23,7 @@ module.exports = function findEmpties(z) {
var thisPt;
var p;
var neighborCount;
var neighborSum;
var newNeighborHash;
var foundNewNeighbors;

Expand Down Expand Up @@ -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;
Expand Down
27 changes: 27 additions & 0 deletions test/jasmine/tests/heatmap_test.js
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Expand Up @@ -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;
Expand Down Expand Up @@ -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);
});
});