llround.c   [plain text]

/*
 * llround.c
 *
 *		by Ian Ollmann
 *
 * Copyright (c) 2007, Apple Inc. All Rights Reserved.
 *
 * C99 implementation of llround.c
 */
 
#include <limits.h>
#include <math.h>
#include <stdint.h>
 
#warning *** untested -- we don't have tests for this

long long llround( double x )
{
	union{ double d; uint64_t u;}u = {x};
	uint64_t absx = u.u & 0x7fffffffffffffffULL;
	
	long long result = (long long) x;	//set invalid / inexact if necessary
	
	if( absx >= 0x4330000000000000ULL )	// 0, large or NaN
	{
		//Deal with overflow cases
		if( x <= (double) LONG_LONG_MIN )
			return LONG_LONG_MIN;

		if( x >= -((double) LONG_LONG_MIN) )
			return LONG_LONG_MAX;
	
		return x;
	}
 
	if( (float) result != x )
	{
		// copysign( 0.5f, x )
		union{ uint64_t u;	double d; } v = { (u.u & 0x8000000000000000ULL) | 0x3fe0000000000000ULL };
		
		if( absx == 0x3fdfffffffffffffULL )
			return result;

		x += v.d;
		
		result = (long long) x;
	}
 
	return result;
}