OSDev.org

Posted: **Sat Jul 14, 2007 4:31 am**

Anyone implemented %f (float) for printf??

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Thomas

Posted: **Sat Jul 14, 2007 4:55 am**

%d is for integers.

Posted: **Sat Jul 14, 2007 5:01 am**

Anyway...

Im interessted in decimal numbers from fpu and how you show them with printf..

-
Thomas

Posted: **Sat Jul 14, 2007 5:31 am**

thomasnilsen wrote:Anyway... Im interessted in decimal numbers from fpu and how you show them with printf..

-
Thomas

Print it as an integer, the add a '.' then subtract the integer from the float, and multiply the float until all digits are left of the decimal point, and print that as an integer. It's easier with C++ since you can just add an "operator<<(float data)" to your console class.

Posted: **Sat Jul 14, 2007 9:05 am**

Hmm but a float is not stored like that??

or is a 32 bit float 10.00000256 stored like [0x0a][0x0000FF] in memory??

If its stored like that then its easy.. but thought it was different.. :-/

cheers
Thomas

Posted: **Sat Jul 14, 2007 9:15 am**

No floats have a special format IEEE 754 that they use to store the number.

Posted: **Sat Jul 14, 2007 9:25 am**

Yes that's what it thougt.. So how do i convert this exponent part to an integer? Cant to any exp maths without floats??

Do i need lookup tables or what?

Im a little bit confused here..

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Thomas

Posted: **Sat Jul 14, 2007 10:29 am**

I think this is more of what they were saying. Note print is just a function that will take a integer and print it.

Code: Select all

void Print_Float( float value )
{
    // print the integral part
    print( (int)value );
    
    // now get rid of the integral part
    value -= ((int)value);
    
    // print the decimal point
    printchar( '.' );
    
    // now the decimal part, make sure everything is to the left
    // of the decimal point.
    // NOTE: You may want to make a cut off after so many tries since this
    // would lock up on numbers like 1/3
    while( value != (int)value )
    {
        value *= 10;
        
    } // end while
    
    // now print it
    print( (int)value );
    
} // end Print_Float

Something like that should work.

Posted: **Sat Jul 14, 2007 10:34 am**

But that wont work.. It wont show the correct value...?

Posted: **Sat Jul 14, 2007 10:39 am**

Yes it will be off a little bit. I just testing it and 1/3 printed 0.33333338. But that is good enough for now don't you think.

Posted: **Sat Jul 14, 2007 10:46 am**

Hmm.. i was thinking the difference would be mouch greater.. This is good enough for me. I will implement right away

Thanks alot.

-
Thomas

Posted: **Sat Jul 14, 2007 4:27 pm**

Its not from my kernel but check this from Tornado OS
http://www.koders.com/info.aspx?c=Proje ... PT8XHKR43D

check ftoa() & sprintf() :
http://www.koders.com/c/fid9E7E7B85C9A3 ... FBAA8.aspx
http://www.koders.com/c/fid88201E3F09A1 ... D2F85.aspx

OSDev.org

prinft implementation for %f

prinft implementation for %f