Fix boundary condition in precisionRound.

src/precisionRound.js

@@ -1,5 +1,6 @@
 import exponent from "./exponent";
 
 export default function(step, max) {
-  return Math.max(0, exponent(Math.abs(max)) - exponent(Math.abs(step))) + 1;
+  step = Math.abs(step), max = Math.abs(max) - step;
+  return Math.max(0, exponent(max) - exponent(step)) + 1;
 };

test/precisionRound-test.js

@@ -0,0 +1,10 @@
+var tape = require("tape"),
+    format = require("../");
+
+tape("precisionRound(step, max) returns the expected value", function(test) {
+  test.equal(format.precisionRound(0.1, 1.1), 2); // "1.0", "1.1"
+  test.equal(format.precisionRound(0.01, 0.99), 2); // "0.98", "0.99"
+  test.equal(format.precisionRound(0.01, 1.00), 2); // "0.99", "1.0"
+  test.equal(format.precisionRound(0.01, 1.01), 3); // "1.00", "1.01"
+  test.end();
+});