7.40. How do I round floating point numbers efficiently?

There are two primary methods for rounding numbers:

Convert.ToInt32
Cast or Fix (C# or VB)
Convert.ToInt32 automatically handles rounding, where remainders of .5 and greater cause the number to be rounded up. Casting or using Fix requires adding .5 to the number to ensure that it will round properly, as these methods simply remove the remainder.

Profiling on the emulator and a Compaq iPAQ H3600 series device yielded the following results for 1 million operations of each method, where num is a float set to 3.6F:

 Emulator
 

 iPAQ
 

 
Operation
 Debug (ms)
 Release (ms)
 Debug (ms)
 Release (ms)
 
C#: Convert.ToInt32(num)
 1321
 1109
 6264
 6283
 
C#: (int)(num + .5F)
 170
 49
 1479
 59
 
VB: Convert.ToInt32(num)
 1218
 1232
 6531
 6517
 
VB: Fix(num + .5F)
 3873
 3677
 18144
 17955
 

Thus, by examining the release build results for the device, it can be concluded that on the current generation of devices it is most efficient to use casting in C# and Convert.ToInt32 in