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fix nice rounding error #283

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fix nice rounding error #283

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13 changes: 9 additions & 4 deletions src/nice.js
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Original file line number Diff line number Diff line change
Expand Up @@ -7,11 +7,16 @@ export default function nice(start, stop, count) {
if (step === prestep || step === 0 || !isFinite(step)) {
return [start, stop];
} else if (step > 0) {
start = Math.floor(start / step) * step;
stop = Math.ceil(stop / step) * step;
const i = Math.ceil(start / step);
const j = Math.floor(stop / step);
start = (i - (i * step > start)) * step;
stop = (j + (j * step < stop)) * step;
} else if (step < 0) {
start = Math.ceil(start * step) / step;
stop = Math.floor(stop * step) / step;
const s = -step;
const i = Math.ceil(start * s);
const j = Math.floor(stop * s);
start = (i - (i / s > start)) / s;
stop = (j + (j / s < stop)) / s;
}
prestep = step;
}
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16 changes: 16 additions & 0 deletions test/nice-test.js
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Expand Up @@ -44,3 +44,19 @@ it("nice(start, stop, count) returns the expected values", () => {
assert.deepStrictEqual(nice(132, 876, 5), [0, 1000]);
assert.deepStrictEqual(nice(132, 876, 1), [0, 1000]);
});

it("nice(start, stop, count) handles small steps precisely", () => {
assert.deepStrictEqual(nice(0.9299999999999999, 1.07, 5000), [0.92998, 1.07]);
assert.deepStrictEqual(nice(-1.07, -0.9299999999999999, 5000), [-1.07, -0.92998]);
assert.deepStrictEqual(nice(0.929999999999999, 1.07, 5000), [0.92998, 1.07]);
assert.deepStrictEqual(nice(-1.07, -0.929999999999999, 5000), [-1.07, -0.92998]);
assert.deepStrictEqual(nice(0.92999999999999, 1.07, 5000), [0.92998, 1.07]);
assert.deepStrictEqual(nice(-1.07, -0.92999999999999, 5000), [-1.07, -0.92998]);
assert.deepStrictEqual(nice(0.930000000000001, 1.07, 5000), [0.93, 1.07]);
assert.deepStrictEqual(nice(-1.07, -0.930000000000001, 5000), [-1.07, -0.93]);
});

it("nice(start, stop, count) handles large steps precisely", () => {
assert.deepStrictEqual(nice(0.929999999999999e10, 1.07e10, 5000), [0.92998e10, 1.07e10]);
assert.deepStrictEqual(nice(-1.07e10, -0.929999999999999e10, 5000), [-1.07e10, -0.92998e10]);
});