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85 lines
3.3 KiB
TypeScript
85 lines
3.3 KiB
TypeScript
export const DECIMAL_RADIX = 10n;
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const SIGN_LENGTH = 1;
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const NEGATIVE_SIGN = -1n;
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const POSITIVE_SIGN = 1n;
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const ZERO_UNITS = 0n;
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const EQUAL = 0;
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const GREATER_THAN = 1;
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const LESS_THAN = -1;
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const INTEGER_SCALE = 0;
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const MIN_WHOLE_DIGITS = 1;
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const DIGITS_START = 0;
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const PREVIOUS_DIGIT_OFFSET = 1;
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const DIGIT_STEP = 1;
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const ROUNDING_DIVISOR = 2n;
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export type Decimal = { scale: number; value: bigint };
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export function decimalFromString(value: string): Decimal {
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// eslint-disable-next-line security/detect-unsafe-regex -- Anchored decimal grammar: the literal decimal point separates disjoint digit runs; backtracking is linear.
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if (!/^-?(?:0|[1-9]\d*)(?:\.\d+)?$/.test(value)) {
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throw new Error('Invalid decimal string');
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}
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const negative = value.startsWith('-');
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const [whole, fraction = ''] = (negative ? value.slice(SIGN_LENGTH) : value).split('.');
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return {
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value: (negative ? NEGATIVE_SIGN : POSITIVE_SIGN) * BigInt(`${whole}${fraction}`),
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scale: fraction.length,
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};
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}
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export function add(left: Decimal, right: Decimal): Decimal {
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const scale = Math.max(left.scale, right.scale);
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return {
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value:
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left.value * DECIMAL_RADIX ** BigInt(scale - left.scale) +
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right.value * DECIMAL_RADIX ** BigInt(scale - right.scale),
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scale,
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};
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}
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export function subtract(left: Decimal, right: Decimal): Decimal {
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return add(left, { value: -right.value, scale: right.scale });
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}
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export function multiply(left: Decimal, right: Decimal): Decimal {
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return { value: left.value * right.value, scale: left.scale + right.scale };
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}
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export function isZero(value: Decimal): boolean {
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return value.value === ZERO_UNITS;
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}
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export function compare(left: Decimal, right: Decimal): number {
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const difference = subtract(left, right).value;
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return difference === ZERO_UNITS ? EQUAL : difference > ZERO_UNITS ? GREATER_THAN : LESS_THAN;
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}
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export function formatDecimal({ value, scale }: Decimal): string {
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if (value === ZERO_UNITS) return '0';
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const sign = value < ZERO_UNITS ? '-' : '';
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if (scale === INTEGER_SCALE) return `${sign}${value < ZERO_UNITS ? -value : value}`;
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const digits = (value < ZERO_UNITS ? -value : value)
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.toString()
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.padStart(scale + MIN_WHOLE_DIGITS, '0');
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const whole = digits.slice(DIGITS_START, -scale) || '0';
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const rawFraction = digits.slice(-scale);
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let fractionEnd = rawFraction.length;
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while (rawFraction.charAt(fractionEnd - PREVIOUS_DIGIT_OFFSET) === '0') fractionEnd -= DIGIT_STEP;
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const fraction = rawFraction.slice(DIGITS_START, fractionEnd);
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const fractionalPart = fraction ? '.' + fraction : '';
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return `${sign}${whole}${fractionalPart}`;
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}
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// Round half away from zero; callers choose presentation precision explicitly.
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export function divide(left: Decimal, right: Decimal, scale: number): Decimal {
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if (right.value === ZERO_UNITS) throw new Error('Division by zero');
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const numerator = left.value * DECIMAL_RADIX ** BigInt(right.scale + scale);
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const denominator = right.value * DECIMAL_RADIX ** BigInt(left.scale);
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const sign = (numerator < ZERO_UNITS) !== (denominator < ZERO_UNITS) ? NEGATIVE_SIGN : POSITIVE_SIGN;
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const n = numerator < ZERO_UNITS ? -numerator : numerator;
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const d = denominator < ZERO_UNITS ? -denominator : denominator;
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return { value: sign * ((n + d / ROUNDING_DIVISOR) / d), scale };
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}
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