static_for.hpp File Reference

A compile time unrolled loop. More...

#include <stdint.h>
#include <utility>
#include <initializer_list>

Go to the source code of this file.

Functions
template<uint8_t N, typename F >
static void	static_for (F &&f)
	Generate a fixed number of calls to a given free function at compile time.

Detailed Description

A compile time unrolled loop.

GCC is surprisingly conservative at unrolling loops with -funroll-loops (and even -funroll-all-loops):

• no nested loops (for, while), which works against inlining.
• if it will increase code size by small margins
• other factors I don't quite understand yet

In summary, it's designed for very simple cases where loop overhead is obviously high

See also

https://godbolt.org/z/6KGWajPaY

Function Documentation

static_for()

template<uint8_t N, typename F >

static void static_for ( F &&  f )

inlinestatic

Generate a fixed number of calls to a given free function at compile time.

Usage:

static inline void foo(uint8_t index, time_t *currTime, const char *message) {
  // Do something
}
 
time_t currTime = time(NULL);
char message[] = "Unrolled!";
// Equivalent of
// foo(3, &currTime, message);
// foo(4, &currTime, message);
// foo(5, &currTime, message);
// foo(6, &currTime, message);
static_for<3, 7>::repeat_n(foo, &currTime, message);

Template Parameters

N	The upper bound (exclusive)
F	Callable type

Parameters

f	Callable instance