OpenEuphoria

Re: POWER()

• Posted by Robert Craig <rds at EMAIL.MSN.COM> Sep 20, 1998
• 597 views

Hawke writes:
> when x*x returns the same value (int,atom,sequence) as
> power(x,2) between 3 and 30 times faster...
> ummmm sumfin wrong dontcha think?

The Euphoria power() function normally
calls the C pow() function which is very general
but very slow. It can handle x to the power of y
for just about any x and y, e.g. 7.88 to the power -2.341

To speed things up, Euphoria detects at execution-time
a couple of special cases such as powers of 2 (which
becomes right-shifts), and small integers raised to small
powers (which become integer multiplies).

Currently, power(x,2) is not optimized when x
is a floating-point number, or a fairly large integer.
x*x is much faster as you have noticed.

For the next release, I'll look into automatically
converting all occurrences of power(x,2) into x*x.
I'll detect this case at compile-time, so no
extra overhead will be added to power().
x could be a simple variable or a complicated
expression. It will be evaluated once, and then
the result will be multiplied by itself.

Usually 2 will be hard-coded into the power()
call. People rarely make the power, i.e. 2,  a
variable or expression when they want to square
something.

Declaring a constant with the value 2 will also
work. e.g.
     constant MYPOWER = 2

This is an example of where declaring
things as "constant" can make your program run faster,
since Euphoria always knows at compile-time what the
value of a constant is.

Regards,
     Rob Craig
     Rapid Deployment Software
     http://members.aol.com/FilesEu/