Simple square-route function if you don't want to use cmath

This is a discussion on Simple square-route function if you don't want to use cmath within the C++ Programming forums, part of the General Programming Boards category; Code: double My_sqrt(int ToSqrt){ /*If you want, make the prompt here. */ double answer=.0000001; while(answer*answer<ToSqrt){ answer+=.0000001;} return answer;} It relies ...

  1. #1
    fuh
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    Simple square-route function if you don't want to use cmath

    Code:
    double My_sqrt(int ToSqrt){
    /*If you want, make the prompt here.
    
    
    */
    double answer=.0000001;
    while(answer*answer<ToSqrt){
    answer+=.0000001;}
    return answer;}
    It relies on loops.You can understand it(duh!).I it doesn't work, I just made it up on a dime.
    Later.
    Stupid things pop singers say

    "I get to go to lots of overseas places, like Canada."
    - Britney Spears

    "I love what you've done with the place!"
    -Jessica Simpson upon meeting the Secretary of Interior during tour of the White House

  2. #2
    Registered User rmullen3's Avatar
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    ...

    Took about 4 seconds to find the square root of 64...
    I think I'll rely on sqrt() which found it in nanoseconds...

    -_-
    Last edited by rmullen3; 01-14-2003 at 04:47 PM.

  3. #3
    Cheesy Poofs! PJYelton's Avatar
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    Wow, it took your computer 40 seconds to do only 8 million calculations? Mine took 1 second. Maybe you should upgrade...

    sqrt() is still obviously faster though!

  4. #4
    fuh
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    Oh, the bad thing is it is slow. I can do some operations faster than it.
    Stupid things pop singers say

    "I get to go to lots of overseas places, like Canada."
    - Britney Spears

    "I love what you've done with the place!"
    -Jessica Simpson upon meeting the Secretary of Interior during tour of the White House

  5. #5
    Registered User rmullen3's Avatar
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    ...

    mistype, meant 4 seconds... *edited*
    Still slow.

    "I can do some operations faster than it."

    Sorry I don't get what you mean?

  6. #6
    Registered User abrege's Avatar
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    Things like that aren't meant to be questioned
    I am against the teaching of evolution in schools. I am also against widespread
    literacy and the refrigeration of food.

  7. #7
    Banned frenchfry164's Avatar
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    I hope you were exaggerating, because I timed it using time() and it reported 4 seconds. I'm using a AMD K6-2 500MHz and compiled it on MSVC++.

  8. #8
    Registered User rmullen3's Avatar
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    ~

    agh ... as I said, mistype... I'm running on 450 mhz, and it took about 4 seconds (4.24).

  9. #9
    Just a Member ammar's Avatar
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    Lightbulb

    Use the function pow()...
    it will do the job!
    none...

  10. #10
    fuh
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    Re: ...


    "I can do some operations faster than it."

    Sorry I don't get what you mean? [/B]
    I meant before it finishes, I'm done.
    Stupid things pop singers say

    "I get to go to lots of overseas places, like Canada."
    - Britney Spears

    "I love what you've done with the place!"
    -Jessica Simpson upon meeting the Secretary of Interior during tour of the White House

  11. #11
    &TH of undefined behavior Fordy's Avatar
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    Code:
    #include <iostream>
    
    int main( void ){
    
    	float	x = 64;
    	
    	__asm{					
    		FLD x			
    		FSQRT			
    		FST x			
    	}
    
    	std::cout << x << std::endl;
    
    	return 0;
    }

  12. #12
    _ Munkey01's Avatar
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    Why use ASM for this? Faster?

  13. #13
    &TH of undefined behavior Fordy's Avatar
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    Originally posted by Munkey01
    Why use ASM for this? Faster?
    Maybe....I was just "adding to the mix"

  14. #14
    moi
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    Re: Simple square-route function if you don't want to use cmath

    Originally posted by fuh
    Code:
    double My_sqrt(int ToSqrt){
    /*If you want, make the prompt here.
    
    
    */
    double answer=.0000001;
    while(answer*answer<ToSqrt){
    answer+=.0000001;}
    return answer;}
    It relies on loops.You can understand it(duh!).I it doesn't work, I just made it up on a dime.
    Later.
    ugggggggg. very slow, very useless, arbitrairly bad precision.
    hello, internet!

  15. #15
    I lurk
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    Code:
    __inline float RSqrt( float number ) {
        long i;
        float x2, y;
        const float threehalfs = 1.5f;
        x2 = number * 0.5f;
        y  = number;
        i  = * (long *) &y;
        i  = 0x5f3759df - (i >> 1);
        y  = * (float *) &i;
        y  = y * (threehalfs - (x2 * y * y));
        return y;
    }
    In all seriousness, I think i'm going to cry.

    If ANYONE can explain to me how that works, i'll make a shrine in your honour and pray at it every day.
    Last edited by Eibro; 01-14-2003 at 08:35 PM.

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