rotate bits.... easy for the pro's

[dave200]

Guys,

I have the value 0x94 (10010100) but want to shift the bits to make 0x29 (00101001)

would the statement below be correct?
If not how would i go about doing so?

[Ttelmah]

First key thing, is that you need a rotation, not a shift. The 'C' >> operator, is a shift. With a shift, when bits get to the 'end' of the byte/word, they are lost off the end.
CCS, has a 'shift_right', and 'shift_left' instruction.
Second thing is though, that if you are dealing with a single byte, if the shift/rotation goes for more than four bits, it is quicker to go the other way round. So in your case, shift left by one, rather than right by seven.
Third thing though, is I presume the value is in a variable, not a constant as you show. Otherwise much quicker for everyone just to just do the shift yourself...

So (for instance):

[dave200]

Thanks Ttelmah!

One thing i did notice in your reply is that you state i require a rotate not shift, but your example shows "shift_left".

Is that correct or do i want the rotate_left?

Thanks and regards

[Wayne_]

Ttelmah is assuming that the MSb of value will always be 1.

To rotate 1 bit to the left

int carry;
int value;

value = 0x94;
carry = (value >> 7);
value = (value << 1) + carry;

OR

rotate_left(&value, 1);

[Ttelmah]

Yes, I meant to use 'rotate'. Shows how easy it is to make mistakes....

Best Wishes

[Humberto]

dave200 wrote: