[RESOLVED] [newbie] What does 1 << VALUE do?

[littlebigman]

Hello

I need to understand what the following line does:

.end   = 0x20000000 + (1 << MAX(VAL1,VAL2)))

What does the syntax "1 << SOMEVALUE" do?

Thank you.

[Skizmo]

bitshifting

[littlebigman]

So, with MYVALUE1=1 and MYVALUE2=2...

#defined MYCONST1 (1<<MYVALUE1)
#defined MYCONST2 (1<<MYVALUE2)

MYCONST1 now contains 2, and MYCONST2 contains 4.

Thanks for the link.

[monarch_dodra]

Yes...

Although technically, there is no MYCONST1 or MYCONST2. What you did was define a macro named MYCONST1, which will be replaced by the text "(1<<MYVALUE1)" wherever it is encountered.

You should do this instead:

const int MYCONST1 (1<<MYVALUE1)
const int MYCONST2 (1<<MYVALUE2)

This has many advantages:
- Avoids errors due to collision: If someone else elsewhere has a "MYCONST1", you will receive a diagnostic
- Makes debugging easier: You'll have an actual symbol named MYCONST1.
- Tighter type safety: MYCONST1 has a pre-defined type. Any conversion that might lose information will give a diagnostic.

[S_M_A]

monarch_dodra was a bit quick there with the copy, paste & edit...

const int MYCONST1 = (1<<MYVALUE1);
const int MYCONST2 = (1<<MYVALUE2);