@formatjs/ecma402-abstract/NumberFormat/ComputeExponent.js

A collection of implementation for ECMAScript abstract operations

import { Decimal } from "@formatjs/bigdecimal";
import "../types/number.js";
import { ComputeExponentForMagnitude } from "./ComputeExponentForMagnitude.js";
import { FormatNumericToString } from "./FormatNumericToString.js";
import { getPowerOf10 } from "./decimal-cache.js";
/**
* The abstract operation ComputeExponent computes an exponent (power of ten) by which to scale x
* according to the number formatting settings. It handles cases such as 999 rounding up to 1000,
* requiring a different exponent.
*
* NOT IN SPEC: it returns [exponent, magnitude].
*/
export function ComputeExponent(internalSlots, x) {
	if (x.isZero()) {
		return [0, 0];
	}
	if (x.isNegative()) {
		x = x.negated();
	}
	// Fast path for simple numbers
	// If x can be represented as a safe integer, use native Math.log10
	const xNum = x.toNumber();
	let magnitude;
	if (Number.isFinite(xNum) && Number.isSafeInteger(xNum) && xNum > 0 && xNum <= 999999) {
		// Use fast native logarithm for simple positive integers
		const magNum = Math.floor(Math.log10(xNum));
		magnitude = new Decimal(magNum);
	} else {
		magnitude = x.log(10).floor();
	}
	const exponent = ComputeExponentForMagnitude(internalSlots, magnitude);
	// Preserve more precision by doing multiplication when exponent is negative.
	x = x.times(getPowerOf10(-exponent));
	const formatNumberResult = FormatNumericToString(internalSlots, x);
	if (formatNumberResult.roundedNumber.isZero()) {
		return [exponent, magnitude.toNumber()];
	}
	// Fast path for simple rounded numbers
	const roundedNum = formatNumberResult.roundedNumber.toNumber();
	let newMagnitude;
	if (Number.isFinite(roundedNum) && Number.isSafeInteger(roundedNum) && roundedNum > 0 && roundedNum <= 999999) {
		const newMagNum = Math.floor(Math.log10(roundedNum));
		newMagnitude = new Decimal(newMagNum);
	} else {
		newMagnitude = formatNumberResult.roundedNumber.log(10).floor();
	}
	if (newMagnitude.eq(magnitude.minus(exponent))) {
		return [exponent, magnitude.toNumber()];
	}
	return [ComputeExponentForMagnitude(internalSlots, magnitude.plus(1)), magnitude.plus(1).toNumber()];
}