Question

unsigned int    error_bits =       

                 ( X && Y )
                 | ( A == TRUE)                         << 1
                 | ( B == TRUE)                         << 2
                 | ( C == TRUE && 
                     D == TRUE)                         << 4;

I believe the general concept here is to set each of the 32 bits to true or false based on certain conditions – with each bit representing an error of something.

With the syntax above, I’m a little confused as to what is being set, shifted and where/why.

Any clarification is helpful.

Thank You.

Answer 1

You are right. The layout of the bits after the line are:

Bits X-5: 0
Bit 4: (C == TRUE && D == TRUE)
Bit 3: 0
Bit 2: B == TRUE
Bit 1: A == TRUE
Bit 0: (X && Y)

From most significant to least significant bit.
Propably something like this would be more readable (a matter of taste):

unsigned int error_bits = 0;

if( X && Y )     
    error_bits |= 1;

if( A == TRUE )     
    error_bits |= 2;

if( B == TRUE )     
    error_bits |= 4;

if( C == TRUE && D == TRUE )     
    error_bits |= 16;