100pah commented on code in PR #21107:
URL: https://github.com/apache/echarts/pull/21107#discussion_r2217334774
##########
src/scale/Log.ts:
##########
@@ -64,9 +64,13 @@ class LogScale extends IntervalScale {
return zrUtil.map(ticks, function (tick) {
const val = tick.value;
- let powVal = fixRound(mathPow(base, val));
+ const rawVal = mathPow(base, val);
let roundingCriterion = null;
+ // Fix #21099
+ const precision = numberUtil.getPrecisionSafe(rawVal) || 0;
+ let powVal = parseFloat(fixRound(rawVal, precision as number,
true));
Review Comment:
@SihongShen @Ovilia I don't fully understand the purpose of this handling.
If `rawVal` has the fractional part digits <= 20, `rawVal` will be equal to
`powVal`, nothing changes.
Otherwise, if the fractional part digits > 20, the `number.round` method
internally clamp it to 20, but that doesn't make sense in this scenario and may
lead incorrect results, e.g, `(1e-40).toFixed(20)` we get `0`.
<img width="743" height="285" alt="image"
src="https://github.com/user-attachments/assets/40d1441e-4764-44fc-b559-9f6801b09be3";
/>
From my understanding, the "fix round" applied in `src/scale` is meant to
correct rounding errors introduced by floating-point computation, (such as the
well-known case where `0.1 + 0.2 === 0.30000000000000004`, when representing
and calculating decimal fractional number in binary).
But `Math.pow(base, tick.value)` shouldn't suffer from such kind of rounding
error, because the `Log.ts` guarantees `interval` and `tick.value` to be
integers, and the `base` is typically an integer as well. They can be exactly
represented in ieee754 64-bit floating-point number (assume no overflow - this
is an separate topic).
Therefore, there is no opportunity for rounding errors to be accumulated
beyond `Number.EPSILON` and result in a different result when converted back to
a decimal string.
(Correct me if I'me wrong.)
Therefore, I think we should just remove this precision and rounding
handling here. Just be:
```js
let powVal = mathPow(base, val);
```
I tried to fix it in https://github.com/apache/echarts/pull/21120
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