[Libre-soc-bugs] [Bug 784] Implement cl* instructions for carry-less operations

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=784

--- Comment #19 from Jacob Lifshay <programmerjake at gmail.com> ---
(In reply to Luke Kenneth Casson Leighton from comment #18)
> 
> that could be achieved with a comment (not too big! the code's really
> elegant and small without the case statement.  something like:
> 
> """
> for i in range(self.width):
>    for each bit a[i] b[i] set addend1[i], addend2[i]
>       case 1,1     both have no leading zeros so far, so set carry 1,1
>       case 0/1 1/0  different number of leading zeros, so clear carry 0,0
>       case 0,0      propagate results from lower bits, so set 1,0
> 
> this is basically equivalent to: addend1 = a^b and addend2 = a|b
> """
> 
> does that look reasonably obvious?

yes, except that the correct ops are XNOR and AND, not XOR and OR

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