A set of functions for doing financial arithmetic. This is a library you could use to build a friendlier money-math library, like the financial-number library.

1. Takes bigints only: value + decimal places (d.p.)
2. Does all math with the native BigInt implementation
3. Multiplication results have d.p. that is twice the d.p. of their inputs. 9.55 * 1.50 = 14.3250
4. Addition and subtraction results have a d.p. as great as the highest d.p. of the two inputs. 1.5 + 1.00 = 2.50

import * as math from 'financial-arithmetic-functions'

Representation of a number

type FinancialNumberValue = {
	value: bigint
	decimal_places: bigint // >=0
}

functions

validate(input)

Can you pass it in to any of the other functions? (i.e. are value and decimal_places both bigints, and is decimal_places >=0)

math.validate({ value: 123n, decimal_places: 0n }) // => true
math.validate({ value: 123444n, decimal_places: 3n }) // => true
math.validate({ value: 123n, decimal_places: -1n }) // => false
math.validate({ value: 123, decimal_places: 0n }) // => false

add(a, b)

math.add({ value: 123n, decimal_places: 0n }, { value: 9999n, decimal_places: 3n }) // => { value: 132999n, decimal_places: 3n }
math.add({ value: 11n, decimal_places: 1n }, { value: 1234n, decimal_places: 3n }) // => { value: 2334n, decimal_places: 3n }
math.add({ value: 5n, decimal_places: 0n }, { value: 987876765654543432321n, decimal_places: 0n }) // => { value: 987876765654543432326n, decimal_places: 0n }

subtract(a, b)

math.subtract({ value: 123n, decimal_places: 0n }, { value: 100n, decimal_places: 0n }) // => { value: 23n, decimal_places: 0n }
math.subtract({ value: 44n, decimal_places: 0n }, { value: -11n, decimal_places: 0n }) // => { value: 55n, decimal_places: 0n }
math.subtract({ value: 10000n, decimal_places: 4n }, { value: 4n, decimal_places: 3n }) // => { value: 9960n, decimal_places: 4n }

multiply(a, b)

math.multiply({ value: 123n, decimal_places: 0n }, { value: 1n, decimal_places: 4n }) // => { value: 123n, decimal_places: 4n }
math.multiply({ value: 9999n, decimal_places: 2n }, { value: 14n, decimal_places: 0n }) // => { value: 139986n, decimal_places: 2n }

modulo(dividend, divisor)

math.modulo({ value: 10n, decimal_places: 0n }, { value: 2n, decimal_places: 0n }) // => { value: 0n, decimal_places: 0n }
math.modulo({ value: 100n, decimal_places: 1n }, { value: 2n, decimal_places: 0n }) // => { value: 0n, decimal_places: 1n }
math.modulo({ value: 1233n, decimal_places: 2n }, { value: 1n, decimal_places: 0n }) // => { value: 33n, decimal_places: 2n }
math.modulo({ value: 1233n, decimal_places: 2n }, { value: 100n, decimal_places: 2n }) // => { value: 33n, decimal_places: 2n }

pow(base, exponent)

math.pow({ value: 2n, decimal_places: 0n }, 3n) // => { value: 8n, decimal_places: 0n }
math.pow({ value: 25n, decimal_places: 1n }, 2n) // => { value: 625n, decimal_places: 2n }
math.pow({ value: 11n, decimal_places: 1n }, 3n) // => { value: 1331n, decimal_places: 3n }

normalizeToSameDecimalPlaces(a, b)

Takes two values and returns their values scaled to the same number of decimal places.

Returns { a: bigint, b: bigint, decimal_places: bigint }.

math.normalizeToSameDecimalPlaces({ value: 12n, decimal_places: 1n }, { value: 3456n, decimal_places: 4n }) // => { a: 12000n, b: 3456n, decimal_places: 4n }
math.normalizeToSameDecimalPlaces({ value: 1234n, decimal_places: 3n }, { value: 56n, decimal_places: 1n }) // => { a: 1234n, b: 5600n, decimal_places: 3n }
math.normalizeToSameDecimalPlaces({ value: 100n, decimal_places: 0n }, { value: 200n, decimal_places: 0n }) // => { a: 100n, b: 200n, decimal_places: 0n }