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new f8f17a58ad GH-45250: [JS] Fix denominator precision loss and remove
unnecessary safe integer check for fractional part (#45251)
f8f17a58ad is described below
commit f8f17a58adb6b5fe4fed6c13d7d3b2e64b4a9acd
Author: Kent Yao <[email protected]>
AuthorDate: Wed Jan 22 11:07:50 2025 +0800
GH-45250: [JS] Fix denominator precision loss and remove unnecessary safe
integer check for fractional part (#45251)
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### Rationale for this change
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### What changes are included in this PR?
This PR uses string constructor for bigint to calculate the power of 10
with scale as the exponent value of the expression.
To Fix precision loss like
```typecript
> BigInt(10) ** BigInt(25);
10000000000000000000000000n
> BigInt(Math.pow(10, 25))
10000000000000000905969664n
```
Also, we remove the unnecessary safe integer check for the fraction
part.
### Are these changes tested?
add some unit tests
### Are there any user-facing changes?
no
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<!-- **This PR contains a "Critical Fix".** -->
* GitHub Issue: #45250
---------
Co-authored-by: Paul Taylor <[email protected]>
---
js/src/util/bn.ts | 11 +++++++----
js/test/unit/bn-tests.ts | 13 ++++++++++++-
2 files changed, 19 insertions(+), 5 deletions(-)
diff --git a/js/src/util/bn.ts b/js/src/util/bn.ts
index 8f6dfe258f..8eed390924 100644
--- a/js/src/util/bn.ts
+++ b/js/src/util/bn.ts
@@ -91,11 +91,14 @@ export function bigNumToNumber<T extends
BN<BigNumArray>>(bn: T, scale?: number)
number |= word * (BigInt(1) << BigInt(64 * i++));
}
}
- if (typeof scale === 'number') {
- const denominator = BigInt(Math.pow(10, scale));
+ if (typeof scale === 'number' && scale > 0) {
+ const denominator = BigInt('1'.padEnd(scale + 1, '0'));
const quotient = number / denominator;
- const remainder = number % denominator;
- return bigIntToNumber(quotient) + (bigIntToNumber(remainder) /
bigIntToNumber(denominator));
+ const remainder = negative? -(number % denominator) : number %
denominator;
+ const integerPart = bigIntToNumber(quotient);
+ const fractionPart = `${remainder}`.padStart(scale, '0');
+ const sign = negative && integerPart === 0 ? '-' : '';
+ return +`${sign}${integerPart}.${fractionPart}`;
}
return bigIntToNumber(number);
}
diff --git a/js/test/unit/bn-tests.ts b/js/test/unit/bn-tests.ts
index 2ea8f6055d..510b8c2cd6 100644
--- a/js/test/unit/bn-tests.ts
+++ b/js/test/unit/bn-tests.ts
@@ -16,7 +16,7 @@
// under the License.
import * as Arrow from 'apache-arrow';
-const { BN } = Arrow.util;
+const { BN, bigNumToNumber } = Arrow.util;
describe(`BN`, () => {
test(`to detect signed numbers, unsigned numbers and decimals`, () => {
@@ -98,4 +98,15 @@ describe(`BN`, () => {
// const n6 = new BN(new Uint32Array([0x00000000, 0x00000000,
0x00000000, 0x80000000]), false);
// expect(n6.valueOf(1)).toBe(1.7014118346046923e+37);
});
+
+ test(`bigNumToNumber`, () => {
+ const n1 = new BN(new Uint32Array([3, 2, 1, 0]));
+ expect(() => bigNumToNumber(n1)).toThrow('18446744082299486211');
+ /* eslint-disable @typescript-eslint/no-loss-of-precision */
+ expect(bigNumToNumber(n1, 10)).toBeCloseTo(1844674408.2299486);
+ expect(bigNumToNumber(n1, 15)).toBeCloseTo(18446.744082299486);
+ expect(bigNumToNumber(n1, 20)).toBeCloseTo(0.18446744082299486);
+ expect(bigNumToNumber(n1, 25)).toBeCloseTo(0.0000018446744082299486);
+ /* eslint-enable @typescript-eslint/no-loss-of-precision */
+ });
});
