Branch-free FizzBuzz in Assembly

Post by [deleted] » Sat, Jan 03, 2015, 8:54 PM UTC

Post by rertrree » Sat, Jan 03, 2015, 9:04 PM UTC

  #include 
  #include 

  const char* table[] = { "%d\n" , "Fizz\n" , "Buzz\n" , "FizzBuzz\n" } ;

  void E( int i )
	{
	    exit( 0 ) ;
	}

  void F( int i )
	{
	        size_t c = !( i%3 ) + !( i%5 )*2 ;
		printf( table[c] , i ) ;
	}

  void ( *func[2] )( int ) = { F , E } ;

  int main( void )
	{
		int p = 1 ;
		while( 1 )
		{
			func[p/102]( p++ ) ;
		}

		return 0 ;
	}

Post by inglor » Sat, Jan 03, 2015, 9:06 PM UTC

Stratoscope wrote: post #3

int ret int ret ret call call call int jmp No conditional branches. As long as you ignore what happens on the other side of those int instructions! Especially that last one...

Post by mikeash » Sat, Jan 03, 2015, 9:08 PM UTC

inglor wrote: post #6

Stratoscope wrote: post #3

int ret int ret ret call call call int jmp No conditional branches. As long as you ignore what happens on the other side of those int instructions! Especially that last one...

Care to elaborate? Isn't `jmp` just a non-conditional jump? How is that branching?

Post by pepijndevos » Sat, Jan 03, 2015, 9:29 PM UTC

rertrree wrote: post #4

This is equivalent code in C if anyone is interested. #include #include const char* table[] = { "%d\n" , "Fizz\n" , "Buzz\n" , "FizzBuzz\n" } ; void E( int i ) { exit( 0 ) ; } void F( int i ) { size_t c = !( i%3 ) + !( i%5 )*2 ; printf( table[c] , i ) ; } void ( *func[2] )( int ) = { F , E } ; int main( void ) { int p = 1 ; while( 1 ) { func[p/102]( p++ ) ; } return 0 ; } This of course only avoids conditional branch…