35 lines
1.3 KiB
JavaScript
35 lines
1.3 KiB
JavaScript
import Decimal from 'decimal.js';
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import { ComputeExponentForMagnitude } from './ComputeExponentForMagnitude';
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import { FormatNumericToString } from './FormatNumericToString';
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/**
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* The abstract operation ComputeExponent computes an exponent (power of ten) by which to scale x
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* according to the number formatting settings. It handles cases such as 999 rounding up to 1000,
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* requiring a different exponent.
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*
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* NOT IN SPEC: it returns [exponent, magnitude].
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*/
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export function ComputeExponent(internalSlots, x) {
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if (x.isZero()) {
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return [0, 0];
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}
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if (x.isNegative()) {
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x = x.negated();
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}
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var magnitude = x.log(10).floor();
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var exponent = ComputeExponentForMagnitude(internalSlots, magnitude);
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// Preserve more precision by doing multiplication when exponent is negative.
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x = x.times(Decimal.pow(10, -exponent));
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var formatNumberResult = FormatNumericToString(internalSlots, x);
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if (formatNumberResult.roundedNumber.isZero()) {
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return [exponent, magnitude.toNumber()];
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}
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var newMagnitude = formatNumberResult.roundedNumber.log(10).floor();
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if (newMagnitude.eq(magnitude.minus(exponent))) {
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return [exponent, magnitude.toNumber()];
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}
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return [
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ComputeExponentForMagnitude(internalSlots, magnitude.plus(1)),
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magnitude.plus(1).toNumber(),
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];
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}
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