ffx.cpp

#include "stdafx.h"

int f( int x )
{
	if( 0 == x )
		return 0;
	if( 0x80000000 == x )
		return 0x80000001;
	const int c = ( ( x >> 31 ) & 1 ) * -2 + 1;
	const int mul = ( x & 1 ) * 2 - 1;
	return c + x * mul;
}

int main()
{
	int tests[] =
	{
		-12, -11, 0, 7, 8
	};
	for( int i : tests )
	{
		printf( "%i\t%i\t%i\n", i, f( i ), f( f( i ) ) );
	}
	return 0;
}