Ceil function: how can we implement it ourselves?

Question

I know that C++ provides us with a ceil function. For practice, I was wondering how can we implement the ceil function in C++. The signature of the method is public static

Answer 1

That is essentially what you have to do, but without converting to string.

A floating-point number is represented as (+/-) M * 2^E. The exponent, E, tells you how far away you are from the binary point^*. If E is big enough, there is no fractional part, so there's nothing to do. If E is small enough, there is no integer part, so the answer is 1 (assuming M is non-zero, and the number is positive). Otherwise, E tells you where the binary point appears within your mantissa, which you can use to do a check, and then perform rounding.

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_{* Not decimal point, because we're in base-2, not base-10.}