Index: node_modules/d3-array/src/fsum.js
===================================================================
--- node_modules/d3-array/src/fsum.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-array/src/fsum.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,69 @@
+// https://github.com/python/cpython/blob/a74eea238f5baba15797e2e8b570d153bc8690a7/Modules/mathmodule.c#L1423
+export class Adder {
+  constructor() {
+    this._partials = new Float64Array(32);
+    this._n = 0;
+  }
+  add(x) {
+    const p = this._partials;
+    let i = 0;
+    for (let j = 0; j < this._n && j < 32; j++) {
+      const y = p[j],
+        hi = x + y,
+        lo = Math.abs(x) < Math.abs(y) ? x - (hi - y) : y - (hi - x);
+      if (lo) p[i++] = lo;
+      x = hi;
+    }
+    p[i] = x;
+    this._n = i + 1;
+    return this;
+  }
+  valueOf() {
+    const p = this._partials;
+    let n = this._n, x, y, lo, hi = 0;
+    if (n > 0) {
+      hi = p[--n];
+      while (n > 0) {
+        x = hi;
+        y = p[--n];
+        hi = x + y;
+        lo = y - (hi - x);
+        if (lo) break;
+      }
+      if (n > 0 && ((lo < 0 && p[n - 1] < 0) || (lo > 0 && p[n - 1] > 0))) {
+        y = lo * 2;
+        x = hi + y;
+        if (y == x - hi) hi = x;
+      }
+    }
+    return hi;
+  }
+}
+
+export function fsum(values, valueof) {
+  const adder = new Adder();
+  if (valueof === undefined) {
+    for (let value of values) {
+      if (value = +value) {
+        adder.add(value);
+      }
+    }
+  } else {
+    let index = -1;
+    for (let value of values) {
+      if (value = +valueof(value, ++index, values)) {
+        adder.add(value);
+      }
+    }
+  }
+  return +adder;
+}
+
+export function fcumsum(values, valueof) {
+  const adder = new Adder();
+  let index = -1;
+  return Float64Array.from(values, valueof === undefined
+      ? v => adder.add(+v || 0)
+      : v => adder.add(+valueof(v, ++index, values) || 0)
+  );
+}