Multiplication vs. register shifting. Which is more efficient?

[japz87]

Hi there... I'm using C18 compiler and came up with this curiosity...

What would be more efficient for a shift operation, for example, if I want to shift a register 7 bits to the left...

register <<= 7;

OR

register *= 128;


thanks!

JAPZ

 

[sina.parsnejad]

shifting
but keep in mind that shifting would only multiply your data with powers of 2

 

[japz87]

Yes, I'm aware of that... my doubt was because I know that the PIC18 has hardware multiplying so if I wanted to do a shift operation I thought maybe it would be more efficient multiplying my variable by powers of 2, instead of using the shift operand (<<).

 

[sina.parsnejad]

yes it is
Unfortunately, most compilers are too stupid to understand that multiplying by a power of 2 is the same as shifting