Can I compute pow(10,x) at compile-time in c?

c compile-time-constant
AShelly picture AShelly · Jun 30, 2009 · Viewed 20.2k times · Source

Is it possible to compute pow(10,x) at compile time?

I've got a processor without floating point support and slow integer division. I'm trying to perform as many calculations as possible at compile time. I can dramatically speed up one particular function if I pass both x and C/pow(10,x) as arguments (x and C are always constant integers, but they are different constants for each call). I'm wondering if I can make these function calls less error prone by introducing a macro which does the 1/pow(10,x) automatically, instead of forcing the programmer to calculate it?

Is there a pre-processor trick? Can I force the compiler optimize out the library call?

Answer

Bill K picture Bill K · Jun 30, 2009

There are very few values possible before you overflow int (or even long). For clarities sake, make it a table!

edit: If you are using floats (looks like you are), then no it's not going to be possible to call the pow() function at compile time without actually writing code that runs in the make process and outputs the values to a file (such as a header file) which is then compiled.

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