Fix denominator precision loss and remove unnecessary safe integer ch…

…eck for fractional part
apache · Jan 14, 2025 · 6ab280a · 6ab280a
1 parent b1bb480
commit 6ab280a
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Showing 2 changed files with 14 additions and 3 deletions.
diff --git a/js/src/util/bn.ts b/js/src/util/bn.ts
@@ -92,10 +92,10 @@ export function bigNumToNumber<T extends BN<BigNumArray>>(bn: T, scale?: number)
         }
     }
     if (typeof scale === 'number') {
-        const denominator = BigInt(Math.pow(10, scale));
+        const denominator = BigInt(10) ** BigInt(scale);
         const quotient = number / denominator;
         const remainder = number % denominator;
-        return bigIntToNumber(quotient) + (bigIntToNumber(remainder) / bigIntToNumber(denominator));
+        return bigIntToNumber(quotient) + Number('0.' + `${remainder}`.padStart(scale, '0'));
     }
     return bigIntToNumber(number);
 }

diff --git 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 = BN.decimal(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 */
+    });
 });