Should I use bit manipulation on float point numbers
bit-manipulation, c++, floating-point
Solution
If your compiler guarantees that you are using IEEE 754 floating-point, I would recommend that you round according to the method delineated in this blog post: add, and then immediately subtract a large constant so as to send the value in the binade of floating-point numbers where the ULP is 0.5. You won't find any faster method, and it does not involve any bit manipulation.
The appropriate constant to round a number between 0 and 32 to the nearest halt-unit for IEEE 754 double-precision is `2251799813685248.0`.
Summary: use `x = x + 2251799813685248.0 - 2251799813685248.0;`.
Problem
I'm writing an algorithm, to round a floating number. The input will be a 64bit IEEE754 double type number, very close to X.5, where X is a integer less than 32. The first solution came into my mind is to use a bit mask, to mask off those least significant bits as they represent very small fractions of 2^-n.(Given the exponent is not large). But the problem is should I do that? Is there any other ways to accomplish the same thing? I feel using bit operation on float point is very controversy. Thanks! The langugage I'm using is C++ by the way. Edit: Thanks guys, for your comments. I appreciate! Let's say I have a float number, can be 1.4999999... or 21.50000012.... I want to round it to 1.5 or 21.5. My goal is to round any number to its nearest to X.5 form, since it can be stored in a IEEE754 float point number.