Dear Eike
I think I have fixed the bugs in my code. Remember is c-like and not c (I used
= instead of ==)
Since I am not a pro programmer I would like to explain to you the logic:
double pow (double number,int exponent)
{
int i=0;
double result=0;
// if the number is zero the result will be zero
if (number==0) return 0; // the bug you were talking about. remember that the
code is c-like not c. i replaced = with ==
// if the number is not zero and the exponent is zero the result will be 1
if (exponent==0) return 1; // another bug
// while the exponent is greater than zero
result=1;
while (exponent)
{
// if exponent modulo 2 is not zero (1) then multiply the result by the number
if (exponent%2) result=result*number;
// set number to it's square
number=number*number;
// divide the exponent with 2
exponent=exponent/2;
}
return result;
}
I will give you a sample of the code inside the loop number=2 and exponent=50
for the loop
0. result=1
1. 1000%2=0, Result=1, Number = Number^2
2. 500%2=0, Result=1, Number = Number^4
3. 250%2=0, Result=1, Number = Number^8
4. 125%2=1, Result=Number^8, Number = Number^16
5. 62%2=0, Result=Number^8, Number = Number^32
6. 31%2=1, Result=Number^40, Number = Number^64
7. 15%2=1, Result=Number^104, Number = Number^128
8. 7%2=1, Result=Number^232, Number = Number^256
9. 3%2=1, Result=Number^488, Number = Number^512
10. 1%2=0, Result=Number^1000, Number = Number^1024
As you can see it need's to run the loop 10 times instead of 1000 and as the
exponent get bigger it seems that it will have less overhead.It's logic
support's only integer exponent's.
Thanks for your time,
Nikos
----- Original Message ----
From: Eike Rathke <[EMAIL PROTECTED]>
To: [email protected]
Cc: Nikos Trivlis <[EMAIL PROTECTED]>
Sent: Tuesday, October 16, 2007 2:49:08 PM
Subject: Re: [dev] Sample code
Hi Nikos,
On Sunday, 2007-10-14 12:04:10 -0700, Nikos Trivlis wrote:
> I have a sample c-like code about how to improve the POW (power
> function) and you could maybe find it useful for calc.
I don't see in what aspect that would improve the POWER code. Au
contraire, the exponent is only integer and doesn't handle floating
point, the loop would introduce a runtime penalty for large exponent
values, but the code is buggy and the loop is never executed. If it was
it wouldn't work either. As is, the function returns 0 for every
combination of arguments.
Eike
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