ccompilationconstantfolding

How effective is constant folding in a C compiler?

My question may be too easy, but I have not found the answer, sorry for that.

if I have some code like this:

...
#define N 6
...
float a, b;
...
a = 2.0 * 3 * N * b;
...

then, after compilation, will this code become something like this?

...
a = 36.0 * b;
...

In other words, the constant part will be calculated at compile time, right?

Thank you in advance.

Solution

  • Most likely, but not guaranteed.

    You can try and look at the disassembly of your program (either in a debugger, or in a disassembler or use a compiler switch (if available) to produce assembly code from your C code).