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June 27, 2019 00:06
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Multiplication with no multiplication, using range reduce
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const isInt = n => parseInt(n) === n; | |
const toPrecisionN = precision => value => | |
Number(value.toPrecision(precision)); | |
function multiplyInt(a, b) { | |
const iterable = [...Array(Math.abs(Math.floor(a)))]; | |
return iterable.reduce( | |
acc => a < 0 | |
? acc - b | |
: acc + b, | |
0 | |
); | |
} | |
function multiply(a, b) { | |
if (isInt(b) && !isInt(a)) { | |
// invert operands for algorhythmic short-circuit | |
return multiplyInt(b, a); | |
} | |
const maxpPrecision = 5; | |
const toPrecision = toPrecisionN(maxpPrecision); | |
const intProduct = multiplyInt(a, b); | |
if (!isInt(a)) { | |
const a$ = parseInt(a) - a; | |
const precisionFactor = Math.pow(10, maxpPrecision); | |
const restProduct = multiplyInt(multiply(precisionFactor, a$), b); | |
const absRestProduct = Math.abs(restProduct / precisionFactor); | |
return toPrecision(intProduct + absRestProduct); | |
} else { | |
return toPrecision(intProduct); | |
} | |
} |
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