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Fix decimal string to fraction conversion #38

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merged 1 commit into from
Jun 16, 2024
Merged

Fix decimal string to fraction conversion #38

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11 changes: 11 additions & 0 deletions src/__tests__/fraction.spec.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -847,4 +847,15 @@ describe('JSON serialization', () => {

expect(data[6]).toBeNull();
});

it('either parses or rejects increasingly accurate decimals', () => {
for (let i = 1; i < 20; ++i) {
try {
const f = new Fraction('0.' + '9'.repeat(i));
expect(f.toFraction()).toBe('9'.repeat(i) + '/' + '1' + '0'.repeat(i));
} catch (e) {
expect(e.message).toBe('Decimal string too complex');
}
}
});
});
45 changes: 29 additions & 16 deletions src/fraction.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -159,19 +159,13 @@ export class Fraction {
this.defloat();
} else if (typeof numerator === 'string') {
numerator = numerator.toLowerCase();
this.n = 1;
this.d = 1;
let exponent: undefined | string;
if (numerator.includes('e')) {
const [mantissa, exponent] = numerator.split('e', 2);
numerator = mantissa;
const e = parseInt(exponent, 10);
if (e > 0) {
this.n = 10 ** e;
} else if (e < 0) {
this.d = 10 ** -e;
}
[numerator, exponent] = numerator.split('e', 2);
}
if (numerator.includes('/')) {
this.n = 1;
if (numerator.includes('.')) {
throw new Error('Parameters must be integer');
}
Expand All @@ -195,15 +189,23 @@ export class Fraction {
} else {
this.s = 1;
}
let m = n ? parseInt(n, 10) : 0;
if (this.n < 0) {
if (n.startsWith('-')) {
throw new Error('Double sign');
}
for (const c of f) {
m = 10 * m + parseInt(c, 10);
this.n = 0;
for (const c of f.split('').reverse()) {
this.n += this.d * parseInt(c, 10);
this.d *= 10;
if (this.d > Number.MAX_SAFE_INTEGER) {
throw new Error('Decimal string too complex');
}
const factor = gcd(this.n, this.d);
this.n /= factor;
this.d /= factor;
}
if (n) {
this.n += parseInt(n, 10) * this.d;
}
this.n *= m;
if (r) {
r = r.replace(/'/g, '');
if (r.length) {
Expand All @@ -212,7 +214,9 @@ export class Fraction {
throw new Error('Cycle too long');
}
const cycleD = (10 ** r.length - 1) * 10 ** f.length;
this.n = this.n * cycleD + this.d * cycleN;
const factor = gcd(cycleD, this.d);
this.d /= factor;
this.n = this.n * (cycleD / factor) + this.d * cycleN;
this.d *= cycleD;
}
}
Expand All @@ -227,6 +231,15 @@ export class Fraction {
if (this.d === 0) {
throw new Error('Division by Zero');
}
if (exponent) {
const e = parseInt(exponent, 10);
if (e > 0) {
this.n *= 10 ** e;
} else if (e < 0) {
this.d *= 10 ** -e;
}
}
this.validate();
this.reduce();
} else {
if (numerator.d === 0) {
Expand All @@ -248,9 +261,9 @@ export class Fraction {
this.n = Math.abs(numerator.n);
this.d = Math.abs(numerator.d);
this.screenInfinity();
this.validate();
this.reduce();
}
this.validate();
}

/**
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