>> c0 = input_carry;
>> for(i=LENGTH;i>0;--i) {
>>   *p++ = ((c1 = (*p & 0x80)) << 1) + c0;
>>   c0 = c1;
>> }
>
>this doesn't. It looks like this'll only write one bit to each byte.

I think that it works ;-), excepting for the oops with c1 inside the
assignment. Ought to be:

c0 = input_carry;
for(i=LENGTH;i>0;--i) {
  c1 = *p & 0x80;
  *p++ = (*p << 1) + c0;
  c0 = c1;
}

It rotates the shift register stored in the vector up by 1 bit (left).

I gave 2 solutions because 'rotating' is ambiguous in meaning. It could be
rotating bits, a matrix, or some other usual target (like serial data).

Peter

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