I have recently been working on shifting a project over from compiling with the MinGW implementation of the GNU C++ compiler to the Microsoft Visual C++ (MSVC) compiler. The most glaring difference is the lack of the rint() function in MSVC. rint(x) takes a double, x, and returns the double value of the closest integer to x. Being a lazy bum I opened the math.h file for MinGW to copy the rint() function to a global win32 compatibility header. Unfortunately, it is written using an assembly instruction and a bunch of macros. Not wanting to copy the macros over, I did the next lazy thing and used Google.
More unfortunately for me, I copied a version of rint() that was not compatible with the implementation in MinGW. I had:
double rint(double x)
{
return floor(x < 0.0 ? x - 0.5 : x + 0.5);
}
It turns out, that this is wrong as -1.5 should be rounded to -1.0 and not -2.0. After wasting a few hours debugging, I finally realised it should be the much simpler:
double rint(double x)
{
return floor(x + 0.5);
}
So much for being a lazy bum...
2 comments:
i thought
-1.5 -> -2.0
-0.5 -> -0.0
0.5 -> 0.0
1.5 -> 2.0
etc, i.e. round to nearest integer and to nearest even for ties (though technically it depends on the GPU's current rounding mode)
sorry for answering a two-year old post, found this accidentally searching for MSVC rint
I am not sure about GPU. The code was for CPU and I doubt rint() had a rounding scheme as in your example.
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