domoritz commented on code in PR #40729:
URL: https://github.com/apache/arrow/pull/40729#discussion_r1536556864
##########
js/src/util/bn.ts:
##########
@@ -68,24 +68,36 @@ Object.assign(SignedBigNum.prototype, BigNum.prototype, {
'constructor': SignedB
Object.assign(UnsignedBigNum.prototype, BigNum.prototype, { 'constructor':
UnsignedBigNum, 'signed': false, 'TypedArray': Uint32Array, 'BigIntArray':
BigUint64Array });
Object.assign(DecimalBigNum.prototype, BigNum.prototype, { 'constructor':
DecimalBigNum, 'signed': true, 'TypedArray': Uint32Array, 'BigIntArray':
BigUint64Array });
+//FOR ES2020 COMPATIBILITY
+const TWO_TO_THE_64 = BigInt(4294967296) * BigInt(4294967296); // 2^64 =
0x10000000000000000n
+const TWO_TO_THE_64_MINUS_1 = TWO_TO_THE_64 - BigInt(1); // (2^32 * 2^32) - 1
= 0xFFFFFFFFFFFFFFFFn
+
/** @ignore */
-function bigNumToNumber<T extends BN<BigNumArray>>(bn: T) {
- const { buffer, byteOffset, length, 'signed': signed } = bn;
- const words = new BigUint64Array(buffer, byteOffset, length);
+export function bigNumToNumber<T extends BN<BigNumArray>>(bn: T, scale?:
number) {
+ const { buffer, byteOffset, byteLength, 'signed': signed } = bn;
+ const words = new BigUint64Array(buffer, byteOffset, byteLength / 8);
const negative = signed && words.at(-1)! & (BigInt(1) << BigInt(63));
- let number = negative ? BigInt(1) : BigInt(0);
- let i = BigInt(0);
+ let number = BigInt(0);
+ let i = 0;
if (!negative) {
for (const word of words) {
- number += word * (BigInt(1) << (BigInt(32) * i++));
+ number |= word * (BigInt(1) << BigInt(64 * i++));
}
} else {
for (const word of words) {
- number += ~word * (BigInt(1) << (BigInt(32) * i++));
+ number |= (word ^ TWO_TO_THE_64_MINUS_1) * (BigInt(1) << BigInt(64
* i++));
}
number *= BigInt(-1);
+ number -= BigInt(1);
+ }
+ if (scale) {
+ const denominator = BigInt(Math.pow(10, scale));
+ const quotient = number / denominator;
+ const remainder = number % denominator;
+ const n = Number(quotient) + (Number(remainder) / Number(denominator));
+ return n;
}
- return number;
+ return Number(number);
Review Comment:
Isn't this incorrect when we have larger numbers?
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