Created
October 15, 2017 13:49
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Операции вычитания, умножения и деления через операцию сложения
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function getNegative(x) { | |
let neg = 0; | |
let sign = x < 0 ? 1 : -1; | |
while (x !== 0) { | |
neg += sign; | |
x += sign; | |
} | |
return neg; | |
} | |
function subtract(first, second) { | |
return first + getNegative(second); | |
} | |
function multiply(first, second) { | |
if (first < second) { | |
return multiply(second, first); // алгоритм будет быстрее, если second < first | |
} | |
let sum = 0; | |
for (let i = Math.abs(second); i > 0; i--) { | |
sum += first; | |
} | |
if (second < 0) { | |
sum = getNegative(sum); | |
} | |
return sum; | |
} | |
function divide(first, second) { | |
if (second === 0) { | |
return null; // error: dividing by zero | |
} | |
let absFirst = Math.abs(first), absSecond = Math.abs(second); | |
let product = 0, result = 0; | |
while (product + absSecond <= absFirst) { | |
product += absSecond; | |
result++; | |
} | |
if ((first < 0 && second < 0) || (first > 0 && second > 0)) { | |
return result; | |
} else { | |
return getNegative(result); | |
} | |
} | |
console.info(subtract(2, 4)); | |
console.info(multiply(3, -4)); | |
console.info(divide(12, -4)); |
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