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GH-45250: [JS] Fix denominator precision loss and remove unnecessary safe integer check for fractional part #45251

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merged 10 commits into from
Jan 22, 2025
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GH-45250: [JS] Fix denominator precision loss and remove unnecessary safe integer check for fractional part #45251

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6ab280a
Fix denominator precision loss and remove unnecessary safe integer ch…
yaooqinn Jan 14, 2025
0e47fd2
Fix denominator precision loss and remove unnecessary safe integer ch…
yaooqinn Jan 14, 2025
6b3ed8e
Fix denominator precision loss and remove unnecessary safe integer ch…
yaooqinn Jan 14, 2025
8825005
Fix denominator precision loss and remove unnecessary safe integer ch…
yaooqinn Jan 14, 2025
5b8f6d9
fix
yaooqinn Jan 15, 2025
97c01c6
Update js/src/util/bn.ts
yaooqinn Jan 20, 2025
08b8150
Update js/src/util/bn.ts
yaooqinn Jan 20, 2025
2f42f3b
Update js/src/util/bn.ts
yaooqinn Jan 20, 2025
adc5c95
Update js/src/util/bn.ts
yaooqinn Jan 20, 2025
e48f2cc
Update js/src/util/bn.ts
yaooqinn Jan 20, 2025
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11 changes: 7 additions & 4 deletions js/src/util/bn.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -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);
}
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13 changes: 12 additions & 1 deletion js/test/unit/bn-tests.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -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`, () => {
Expand Down Expand Up @@ -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 */
});
});
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