_nextafterf on Visual C++

I need to use the function _nextafterf on Visual C++ 32 bit to compute the distance in ULP of some results compare to reference func开发者_Python百科tions.

C99 provides nextafterf and nextafter for float and double but these functions are not supported by Visual C++. However, Visual C++ 2010 supports _nextafterf and nextafter from but only in 64 bits... With the 32 bits model only _nextafter is support and from ...

Is there a way to get _nextafterf working on Visual Studio maybe up to Visual C++ 2005?

Thanks, Christophe

There is a templatized equivalent nextafter in Boost.Math, see Finding the Next Representable Value in a Specific Direction (nextafter).

The C99 functions must use suffixes f and l to distinguish float and long double versions. C++ uses the template mechanism instead.

You can always implement it...

https://www.google.com/search?q=libm%2Fsrc%2Fs_nextafterf.c

found a code here:

/*
 *  nextafterf.c
 *  cLibm
 *
 *  Created by Ian Ollmann on 6/14/07.
 *  Copyright 2007 Apple Inc. All rights reserved.
 *
 */
...
float nextafterf( float x, float y )
{
union{ float f; uint32_t u;} ux = { x };
uint32_t    step = 1;

if( y != y || x != x)
    return x + y;

if( y <= x ) // a subtraction here would risk Inf-Inf
{
    if( y == x )
        return y;   //make sure sign of 0 is correct

    step = -1;
}

//correct for the sign
int32_t signMask = (int32_t) ux.u >> 31;
step = (step ^ signMask) - signMask;

uint32_t absux = ux.u & 0x7fffffffU;

if( absux == 0 )                // zero
{
    ux.f = y;
    ux.u = (ux.u & 0x80000000U) + 1U;
    return ux.f;
}

ux.u += step;
return ux.f;
}

http://www.opensource.apple.com/source/Libm/Libm-315/Source/ARM/nextafterf.c

work?