Handling Floating-Point exceptions in C++

Question

I\'m finding the floating-point model/error issues quite confusing. It\'s an area I\'m not familiar with and I\'m not a low level C/asm programmer, so I would appreciate a b

Answer 1

Most of the the following information comes from Bruce Dawson's blog post on the subject (link).

Since you're working with C++, you can create a RAII class that enables or disables floating point exceptions in a scoped manner. This lets you have greater control so that you're only exposing the exception state to your code, rather than manually managing calling _controlfp_s() yourself. In addition, floating point exception state that is set this way is system wide, so it's really advisable to remember the previous state of the control word and restore it when needed. RAII can take care of this for you and is a good solution for the issues with GDI+ that you're describing.

The exception flags _EM_OVERFLOW, _EM_ZERODIVIDE, and _EM_INVALID are the most important to account for. _EM_OVERFLOW is raised when positive or negative infinity is the result of a calculation, whereas _EM_INVALID is raised when a result is a signaling NaN. _EM_UNDERFLOW is safe to ignore; it signals when your computation result is non-zero and between -FLT_MIN and FLT_MIN (in other words, when you generate a denormal). _EM_INEXACT is raised too frequently to be of any practical use due to the nature of floating point arithmetic, although it can be informative if trying to track down imprecise results in some situations.

SIMD code adds more wrinkles to the mix; since you don't indicate using SIMD explicitly I'll leave out a discussion of that except to note that specifying anything other than /fp:fast can disable automatic vectorization of your code in VS 2012; see this answer for details on this.