A negative number (-A5) is the twos compliment of the positive number. A ones compliment is all the bits flipped. A twos compliment is a ones compliment plus one. So a ones compliment of (A5) is (-A5 - 1), which is -A6.
So presumably, the twos compliment operator is (-). And I suppose for consistency, +-A5 gives you -A5, which makes +- the twos compliment bitwise operator.. On Tue, Jan 14, 2020 at 7:45 AM Paul Procacci <pproca...@gmail.com> wrote: > >> What is the syntax for a twos complement anyway? > > I'm not sure I understand the question. > Two's compliment is +^ ... the routine you've been using. > > On Tue, Jan 14, 2020 at 12:33 AM ToddAndMargo via perl6-users < > perl6-us...@perl.org> wrote: > >> >> On Mon, Jan 13, 2020 at 11:30 PM ToddAndMargo via perl6-users >> >> <perl6-us...@perl.org <mailto:perl6-us...@perl.org>> wrote: >> >> >> >> Hi All, >> >> >> >> This works, >> >> >> >> $ p6 'my uint8 $c = 0xA5; my uint8 $d = +^$c; say >> $d.base(16);' >> >> 5A >> >> >> >> But this does not: >> >> >> >> $ p6 'my uint8 $c = 0xA5; say (+^$c).base(16);' >> >> -A6 >> >> >> >> 1) who turned it into an negative integer? >> >> >> >> 2) how do I turn it back? >> >> >> >> Many thanks, >> >> -T >> >> On 2020-01-13 21:18, Paul Procacci wrote: >> > If you read the signature for +^, you'll notice it returns an Int. >> > >> > In your first working example, you're taking a uint8 with binary value >> > 10100101, zero extending it to 64 bits via +^, applying a two's >> > compliment, and then assigning bits [0:7] to another uint8 which at >> that >> > point contains the binary value of 01011010 (or hex value 0x5A). >> > In your second example that isn't working, you're taking uint8 with >> > binary value 10100101, zero extending it to 64 bits via +^, applying a >> > two's compliment, and then displaying this *Int* (64 bits) as hex.[1] >> > To turn it back you need to mask off bits [8:63] with: say ((+^$e) +& >> > 0x0FF).base(16);" [2] >> > >> > [1] I'd show you the 64 bit value but it's a bunch of 1's followed by >> > the value -0xA6. >> > [2] Note, since the type has been promoted to an Int there' no going >> > back to uint8 without an explicit assignment (afaik) >> > >> >> That explains it. Thank you. >> >> I used uint8 to keep the ones to a mild torrent! >> >> If I am remembering correctly, 0xA5 going to 0x5A is >> a ones compliment. >> >> What is the syntax for a twos complement anyway? > > >> > > -- > __________________ > > :(){ :|:& };: >
