CODEWITHSUNDEEP
javascriptfloating-pointcompare
dotty
dotty

Reputation: 41483

comparing two floats to see if they're both negative, or both positive

Hay guys, i have 2 floats, which both comes from input boxes.

I need to compare these 2 floats, if one is negative and one is positive thrown an error. If they're both positive, or both negative, thats fine.

Any ideas?

Thanks

Upvotes: 2

Views: 2869

Answers (4)

marcgg
marcgg

Reputation: 66485

function isSameSign(a,b){
  var r = a*b; 
  return (r >= 0)
}

Upvotes: 0

ChrisF
ChrisF

Reputation: 137178

Multiply them together.

If the answer is positive then they are both the same sign.

If the answer is negative then they are of opposite sign.

If the answer is zero (within some value to take care of rounding error) then one or both are zero and you'll have to check them individually. You'll then have to decide whether 0 to be treated as positive or negative in your scenario.

Upvotes: 12

xtofl
xtofl

Reputation: 41519

Although detection of the sign of the product can be done, it's not what you are interested in. Especially if you're going to use it on large volumes of floats (eg to detect a zero crossing in a time stream).

The simplest way is to exactly express what you ask for: is the sign of a equal to the sign of b?

function samesign( a, b ) {
  var aPositive = a >= 0;
  var bPositive = b >= 0;
  return aPositive == bPositive;
}

Or shorter:

function samesign( a, b ) { return (a>=0) == (b>=0); }

Upvotes: 8

Seth Moore
Seth Moore

Reputation: 3545

Just do something like:

if float1*float2<0
    Error

Upvotes: 2

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