Integer Floating point library for arm4t?

[Jared Maddox]

> cchandel wrote:
> Hi,
>  I wrote guitartuner a while ago - and found that the large number of
> floating point operations were a major bottleneck.
>  Can anyone point me to an opensource implementation of int based floating
> point calculations that I could use without any licensing issues for
> development on the FR?
I don't have a floating point library, but the following fixed point
code should be (approximately) right:

enum unsigned_fixed_special_values
{
	underflow : 65533,
	overflow : 65534,
	invalid : 65535,
	
	low_mask : 255,
	high_mask : 65280,
	
	high_offset : 256
};

unsigned unsigned_fixed_add( unsigned a, unsigned b )
{
	unsigned r;
	
	r = a + b;
	
	if( r >= underflow )
	{
		r = overflow;
	}
	
	return( r );
}

unsigned unsigned_fixed_sub( unsigned a, unsigned b )
{
	if( b < a )
	{
		return( underflow );
	} else {
		return( a + b );
	}
}

int unsigned_fixed_mul( unsigned num, unsigned den )
{
	unsigned den_a, den_b, tmp;
	
	den_b = ( den & high_mask ) / high_offset;
	
	if( ( num & high_mask ) / high_offset * ( den_b ) > low_mask )
	{
		return( overflow );
	}
	
	den_a = den & low_mask;
	
	tmp = ( num * den_b ) + ( num / den_a );
	
	if( tmp >= high_mask | low_mask )
	{
		tmp = overflow;
	}
	
	return( tmp );
}

unsigned unsigned_fixed_div( unsigned num, unsigned den )
{
	unsigned den_a, den_b, tmp;
	
	if( den & ( low_mask & high_mask ) == 0 )
	{
		return( invalid );
	}
	
	den_a = den & low_mask;
	
	if( ( num & high_mask ) / high_offset * ( den_a ) > low_mask )
	{
		return( overflow );
	}
	
	den_b = ( den & high_mask ) / high_offset;
	
	tmp = ( num * den_a ) + ( num / den_b );
	
	if( tmp >= high_mask | low_mask )
	{
		tmp = overflow;
	}
	
	return( tmp );
}

Beware that it hasn't been tested. It only does unsigned, but it can
handle signed with some simple wrapper functions. Also, I write in
C++, so I don't know how long names are allowed to be in C. I don't
remember whether enums are allowed to be accessed like that (I deal
with those things when compiling, not coding).

This code is for 16-bit floating point. Adjust it as needed. I didn't
try for underflow checking on the multiply/divide functions.