57 lines
1.6 KiB
JavaScript
57 lines
1.6 KiB
JavaScript
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import { factory } from '../../utils/factory.js';
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var name = 'invmod';
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var dependencies = ['typed', 'config', 'BigNumber', 'xgcd', 'equal', 'smaller', 'mod', 'add', 'isInteger'];
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export var createInvmod = /* #__PURE__ */factory(name, dependencies, _ref => {
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var {
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typed,
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config,
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BigNumber,
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xgcd,
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equal,
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smaller,
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mod,
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add,
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isInteger
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} = _ref;
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/**
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* Calculate the (modular) multiplicative inverse of a modulo b. Solution to the equation `ax ≣ 1 (mod b)`
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* See https://en.wikipedia.org/wiki/Modular_multiplicative_inverse.
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*
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* Syntax:
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*
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* math.invmod(a, b)
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*
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* Examples:
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*
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* math.invmod(8, 12) // returns NaN
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* math.invmod(7, 13) // return 2
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* math.invmod(15151, 15122) // returns 10429
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*
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* See also:
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*
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* gcd, xgcd
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*
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* @param {number | BigNumber} a An integer number
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* @param {number | BigNumber} b An integer number
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* @return {number | BigNumber } Returns an integer number
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* where `invmod(a,b)*a ≣ 1 (mod b)`
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*/
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return typed(name, {
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'number, number': invmod,
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'BigNumber, BigNumber': invmod
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});
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function invmod(a, b) {
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if (!isInteger(a) || !isInteger(b)) throw new Error('Parameters in function invmod must be integer numbers');
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a = mod(a, b);
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if (equal(b, 0)) throw new Error('Divisor must be non zero');
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var res = xgcd(a, b);
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res = res.valueOf();
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var [gcd, inv] = res;
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if (!equal(gcd, BigNumber(1))) return NaN;
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inv = mod(inv, b);
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if (smaller(inv, BigNumber(0))) inv = add(inv, b);
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return inv;
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}
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});
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