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Commitab7755a

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adityahirantrekhleb
authored andcommitted
feat(bitwise): Function to check if a number is positive (trekhleb#204)
1 parent861e0e9 commitab7755a

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4 files changed

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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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importisPositivefrom'../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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});
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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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exportdefaultfunctionisPositive(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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returnfalse;
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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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importmultiplyByTwofrom'./multiplyByTwo';
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importdivideByTwofrom'./divideByTwo';
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importisEvenfrom'./isEven';
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importisPositivefrom'./isPositive';
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/**
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* Multiply two signed numbers using bitwise operations.
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constmultiplyByOddNegative=()=>multiply(multiplyByTwo(a),divideByTwo(b+1))-a;
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constmultiplyByEven=()=>multiply(multiplyByTwo(a),divideByTwo(b));
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constmultiplyByOdd=()=>(b>0 ?multiplyByOddPositive() :multiplyByOddNegative());
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constmultiplyByOdd=()=>(isPositive(b) ?multiplyByOddPositive() :multiplyByOddNegative());
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returnisEven(b) ?multiplyByEven() :multiplyByOdd();
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}

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