Left shift question

GhostofK · Guest

Hi, I'm working on a school project and I have another question about some code. I'm trying to do a left shift on a variable named 'mask'. If I write:
int16 mask = 1;
mask = mask << 1;
then will the result be mask = 10 or mask = 11?

The code that I'm using is right below as well.

void drive_led(int16 code){
int16 code_bit = 0x0000;
int16 mask = 0x0001;

delay_ms(20);
output_high(PIN_C1);
delay_ms(2400);
output_low(PIN_C1);
delay_ms(600);

while(mask != 0x1000){
code_bit = code && mask;
if(code_bit != mask){
output_high(PIN_C1);
delay_us(600);
output_low(PIN_C1);
delay_us(600);
}
else{
output_high(PIN_C1);
delay_us(1200);
output_low(PIN_C1);
delay_us(600);
}
mask = mask << 1;
}
}

Thanks for any help!

newguy · Joined: 24 Jun 2004 Posts: 1911

After the shift operation mask will be 0x02 (binary 10). Shifts always shift in zeroes.

Ttelmah · Guest

<<, is equivalent to multiplying by two. So binary 001, becomes '010'.
If you want to shift a value in, then look at the 'shift left' command. This allows a value to be shifted in to fill the bottom bit. So:

GhostofK · Guest

Thanks for the help!

GhostofK · Joined: 04 Jun 2006 Posts: 6

Hi, I'm having some trouble with my code that I posted above originally. For some reason, pin C1 is not going all the way high. The timing is perfect, but pin_C1 is only going up to about 600mV instead of the full 5v as it should. Does anyone know what could be the problem here?