The standard C library has 4 floating point rounding modes available through
cfenv.h. These are now available in C++11 through the header file
- The 4 floating point rounding modes are:
FE_TONEAREST FE_DOWNWARD FE_UPWARD FE_TOWARDZERO
FE_TONEARESTrounds to the nearest integer. If the floating point value is exactly midway between two integers, then it does round half to even. The rest of the rounding modes are self explanatory.
None of the 4 rounding modes is equivalent to the round half away from zero which the
Anything to do with floating point operations is dependent on the FPU of the processor. So, the availability of these rounding modes and their values are highly dependent on the FPU of your processor.
On my x86_64 computer, all the 4 rounding modes were available and the values of these rounding modes were found to be:
#define FE_TONEAREST 0x000 #define FE_DOWNWARD 0x400 #define FE_UPWARD 0x800 #define FE_TOWARDZERO 0xC00
The FPU of your processor may support many other rounding modes in addition to these 4 modes.
On my x86_64 computer, I found that
FE_TONEARESTwas the default rounding mode when I used methods like
nearbyintto perform rounding.