Return Negative Float? - GameCreators Forum

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Tv Xxx

16

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Joined: 23rd Sep 2007

Location: Behind You!

Posted: 5th Apr 2009 20:27

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I'm just messing around with making a dll, and I can't make it return a negative float...

its the quadratic equation...

+ Code Snippet

#include "stdafx.h"
#include "math.h"

BOOL APIENTRY DllMain( HANDLE hModule, 
                       DWORD  ul_reason_for_call, 
                       LPVOID lpReserved
					 )
{
    return TRUE;
}

#define MYCOMMAND __declspec ( dllexport )

MYCOMMAND DWORD Tv_Quad( int p , float a, float b, float c )
{
	float result;
	
	if (p = 1)
	{
		result = (( -b ) + sqrt(( b * b ) - ( 4.0f * a * c ))) / ( 2.0f * a );
	}
	else
	{
		result = (( -b ) - sqrt(( b * b ) - ( 4.0f * a * c ))) / ( 2.0f * a );
	}

	return *(DWORD*)&result;
}

it runs in DBpro, and returns the positive float fine, but the negative just returns 0...

any ideas?

Yours Tv.

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chunks chunks

16

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Joined: 2nd Jan 2007

Location: ackworth uk

Posted: 6th Apr 2009 21:03

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hasn`t it got to be signed to use negative values i`m not sure with floats but thats the case with ints .

chunks

nvidia geforce 8600gt + amd athlon 64
windows xp pro.

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Rudolpho

17

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Joined: 28th Dec 2005

Location: Sweden

Posted: 7th Apr 2009 22:58

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Yeah, well, first out you're using a DWORD, which is definitively not a float...
Furthermore, as chunks said, a DWORD is unsigned, so even if the cast actually succeeds it wouldn't be able to yield any negative values.

What's the deal with the DWORD part anyway, can't you just return the float?

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Tv Xxx

16

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Joined: 23rd Sep 2007

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Posted: 7th Apr 2009 23:20

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I dunno why it has to be a DWORD but thats what it said in the help files in dbpro...

yours Tv

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Diggsey

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Joined: 24th Apr 2006

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Posted: 8th Apr 2009 00:20

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The DWORD part is correct. (If you use float, C++ passes it through one of the floating point registers instead of pushing it onto the stack).

The reason it is always positive is simple, you are checking 'if (p = 1)'

What that does is assigns 1 to p, and then checks if p is non-zero. What you want is:
'if (p == 1)'

[b]Yuor signutare was aresed by a deslyxic mud...
BOX2D V2 HAS HELP FILES! AND A WIKI!

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DLL Talk / Return Negative Float?