Common location operations in C Language

From: http://blog.ednchina.com/jimmy_qiu/78829/message.aspx

 

How to Set 0 or 1 for a certain position?
Method 1: Write a macro to facilitate migration
# Define setbit (x, y) x | = (1 <Y) // set position y of X to 1.
# Define clrbit (x, y) X & =! (1 <Y) // clears the Y position of X to 0. Method 2: In addition to improving the operation efficiency, the C language bit operation is another typical application in embedded system programming, in addition, it is widely used in scenarios such as bitwise AND (&), or (|), non (~) Operation, which is closely related to the programming features of embedded systems. We usually need to set the bit of the hardware register, for example, by setting the Lower 6 bits of the interrupt Shield Control Register of the am186er 80186 processor to 0 (on interrupt 2 ), the most common practice is:

# Define int_i2_mask 0x0040
Wtemp = inword (int_mask );
Outword (int_mask, wtemp &~ Int_i2_mask );

The method to set this bit to 1 is:

# Define int_i2_mask 0x0040
Wtemp = inword (int_mask );
Outword (int_mask, wtemp | int_i2_mask );

To determine whether the bit is 1 is:

# Define int_i2_mask 0x0040
Wtemp = inword (int_mask );
If (wtemp & int_i2_mask)
{
... /* This bit is 1 */
}

Method 3: int A | = (1 <X) // X indicates the number to be set to 1. For example, the fourth position is a | = (1 <4)
Int B & = ~ (1 <X) // set a position 0x = x | 0x0100 // set the third position 1
X = x & 0x1011 // set the third position to 0 # define bitget (number, POS) (number)> (POS) & 1 )) // use a macro to obtain a certain number
# Define bitget (number, POS) (number) | = 1 <(POS) // set a location of 1
# Define bitget (number, POS) (number) & = ~ (1 <(POS) // set a position to 0
# Define bitget (number, POS) (number) ^ = 1 <(POS) // a typical anti-pos operation for Number:
Wtcon | = (1 <5) // The fifth-digit clearance of wtcon 1
Wtcon & = ~ (1 <5) // The fifth digit of wtcon is 0.