How to compare double or float in Cpp

From MetaSharp

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definition of the double type

The following code is the best way I could come up with to work correctly with doubles. The float version is not provided yet, but after reading a bit the code, you should manage to easily extend it to floats. The most important functions here are:

• GetExpoBase2() extracts the base2 exponent from the double (putting aside the sign bit and the mantissa)
• Equals() gets the exponents (e1,e2) of both doubles (d1,d2) and the exponent (e3) of their difference (d1-d2), then the 2 doubles (d1,d2) are considered being equal only if their difference is close enough to 0. This is done comparing the exponents. Example: e3=-50 (meaning 2^-50) e1=-1 e2=-1 then e3-e2=-49 and e3-e1=-49 both less than -48. It means that e1 and e2 are equal because their difference significant bits are located 2^48 lower... hard to tell if it's clear enough, I'll edit later if I come up with a clearer explaination ^^

Download Double comparison Sample for VC2005

compare.cpp

// compare.cpp
#include "compare.h"

namespace metasharp
{
	inline int GetExpoBase2(double d)
	{
		int i = 0;
		((short *)(&i))[0] = (((short *)(&d))[3] & (short)32752); // _123456789ab____ & 0111111111110000
		return (i >> 4) - 1023;
	}

	bool	Equals(double d1, double d2)
	{
		if (d1 == d2)
			return true;
		int e1 = GetExpoBase2(d1);
		int e2 = GetExpoBase2(d2);
		int e3 = GetExpoBase2(d1 - d2);
		if ((e3 - e2 < -48) && (e3 - e1 < -48))
			return true;
		return false;
	}

	int 	Compare(double d1, double d2)
	{
		if (Equals(d1, d2) == true)
			return 0;
		if (d1 > d2)
			return 1;
		return -1;
	}

	bool	Greater(double d1, double d2)
	{
		if (Equals(d1, d2) == true)
			return false;
		if (d1 > d2)
			return true;
		return false;
	}

	bool	GreaterOrEqual(double d1, double d2)
	{
		if (Equals(d1, d2) == true)
			return true;
		if (d1 > d2)
			return true;
		return false;
	}

	bool	Less(double d1, double d2)
	{
		if (Equals(d1, d2) == true)
			return false;
		if (d1 < d2)
			return true;
		return false;
	}

	bool	LessOrEqual(double d1, double d2)
	{
		if (Equals(d1, d2) == true)
			return true;
		if (d1 < d2)
			return true;
		return false;
	}
}

compare.h

// compare.h
#ifndef COMPARE_H
#define COMPARE_H

namespace metasharp
{
	int 	Compare(double d1, double d2);
	bool	Equals(double d1, double d2);
	bool	Greater(double d1, double d2);
	bool	GreaterOrEqual(double d1, double d2);
	bool	Less(double d1, double d2);
	bool	LessOrEqual(double d1, double d2);
}

#endif