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fix(maths): prevent float rounding error in numberOfDigitsUsingLog for large safe integers #2029

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fix(maths): prevent float rounding error in numberOfDigitsUsingLog for large safe integers #2029

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24 changes: 21 additions & 3 deletions Maths/NumberOfDigits.js
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Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,12 @@
*
*/

const numberOfDigit = (n) => Math.abs(n).toString().length
const numberOfDigit = (n) => {
if (typeof n !== 'number' || !Number.isFinite(n)) {
throw new TypeError('Input must be a finite number')
}
return Math.abs(Math.trunc(n)).toString().length
}

/**
* Returns the number of digits of a given integer.
Expand All @@ -17,7 +22,20 @@ const numberOfDigit = (n) => Math.abs(n).toString().length
* @see https://math.stackexchange.com/questions/2145480/how-does-the-logarithm-returns-the-number-of-digits-of-a-number
* @author dev-madhurendra
*/
const numberOfDigitsUsingLog = (n) =>
n === 0 ? 1 : Math.floor(Math.log10(Math.abs(n))) + 1
const numberOfDigitsUsingLog = (n) => {
if (typeof n !== 'number' || !Number.isFinite(n)) {
throw new TypeError('Input must be a finite number')
}
const intVal = Math.trunc(n)
if (intVal === 0) return 1
const abs = Math.abs(intVal)
let digits = Math.floor(Math.log10(abs)) + 1
if (Math.pow(10, digits - 1) > abs) {
digits--
} else if (Math.pow(10, digits) <= abs) {
digits++
}
return digits
}

export { numberOfDigit, numberOfDigitsUsingLog }
13 changes: 12 additions & 1 deletion Maths/test/NumberOfDigits.test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -13,11 +13,22 @@ describe('NumberOfDigits', () => {
[0, 1],
[123423232, 9],
[-123423232, 9],
[9999, 4]
[9999, 4],
[999999999999999, 15],
[1000000000000000, 16],
[1000000000000001, 16]
])(
'should return the correct number of digits in an integer',
(value, expected) => {
expect(numberOfDigitsUsingLog(value)).toBe(expected)
expect(numberOfDigit(value)).toBe(expected)
}
)

it('should throw TypeError for invalid inputs', () => {
expect(() => numberOfDigit('123')).toThrow(TypeError)
expect(() => numberOfDigit(NaN)).toThrow(TypeError)
expect(() => numberOfDigitsUsingLog('123')).toThrow(TypeError)
expect(() => numberOfDigitsUsingLog(NaN)).toThrow(TypeError)
})
})
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