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Commit ab7755a

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adityahirantrekhleb
authored andcommitted
feat(bitwise): Function to check if a number is positive (trekhleb#204)
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‎src/algorithms/math/bits/README.md

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@@ -51,6 +51,29 @@ isEven: true
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> See [isEven.js](isEven.js) for further details.
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#### isPositive
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This method determines if the number provided is positive.
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It is based on the fact that all positive numbers have their last
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left bit to be set to 0. However, if the number provided is zero
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or negative zero, it should still return false.
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```text
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Number: 1 = 0b0001
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isPositive: true
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Number: -1 = -0b0001
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isPositive: false
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Number: 0 = 0b0000
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isPositive: false
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Number: -0 = 0b0000
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isPositive: false
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```
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> See [isPositive.js](isPositive.js) for further details.
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#### Multiply By Two
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This method shifts original number by one bit to the left.
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import isPositive from '../isPositive';
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describe('isPositive', () => {
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it('should detect if a number is positive', () => {
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expect(isPositive(0)).toBe(false);
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expect(isPositive(-0)).toBe(false);
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expect(isPositive(1)).toBe(true);
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expect(isPositive(-1)).toBe(false);
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});
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});

‎src/algorithms/math/bits/isPositive.js

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/**
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* @param {number} number
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* @return {boolean}
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*/
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export default function isPositive(number) {
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// Zero is neither a positive nor a negative number
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if (number === 0) {
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return false;
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}
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// The most signification bit can be used to determine whether .
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return ((number >> 31) & 1) === 0;
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}

‎src/algorithms/math/bits/multiply.js

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import multiplyByTwo from './multiplyByTwo';
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import divideByTwo from './divideByTwo';
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import isEven from './isEven';
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import isPositive from './isPositive';
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/**
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* Multiply two signed numbers using bitwise operations.
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const multiplyByOddNegative = () => multiply(multiplyByTwo(a), divideByTwo(b + 1)) - a;
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const multiplyByEven = () => multiply(multiplyByTwo(a), divideByTwo(b));
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const multiplyByOdd = () => (b>0 ? multiplyByOddPositive() : multiplyByOddNegative());
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const multiplyByOdd = () => (isPositive(b) ? multiplyByOddPositive() : multiplyByOddNegative());
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return isEven(b) ? multiplyByEven() : multiplyByOdd();
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}

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