Slightly OT: speed of operation on a PC

On 04.08.2015 20:06, Lanarcam wrote:
> Le 04/08/2015 19:59, Tim Wescott a écrit :
>> Which do you think is quicker on a PC, with the latest gnu compiler:
>>
>> double a = something;
>> double b = something else;
>>
>> if (a >= 0.0 && b < 0.0)
>>
>>>> or <<
>>
>> if (a * b <= 0)
>>
>> Thank you for your time.
>>
> if (a + b < a) would be quicker, I believe.

Why would it? Depending on the architecture, comparing with 0 is often
more efficient than with other values. Also multiplication is a much
simpler operation than addition for floating-point values.

Philipp

On 04.08.2015 23:30, Hans-Bernhard Bröker wrote:
> Am 04.08.2015 um 19:59 schrieb Tim Wescott:
>> Which do you think is quicker on a PC, with the latest gnu compiler:
>>
>> double a = something;
>> double b = something else;
>>
>> if (a >= 0.0 && b < 0.0)
>>
>>>> or <<
>>
>> if (a * b <= 0)
> 
> That's rather beside the point, I'm afraid.  Those two expressions don't
> even compute the same condition, so who cares which of them might be
> quicker?

They might be equivalent for the OP. The OP might have additional
knowledge on the values of a and b.

Philipp