2 Oct
2006
2 Oct
'06
8:24 p.m.
No.
On PDP 11 assembler the left and right shifts were a single < and >.
You made a typo when transcribing the source statement: you typed
0636: mov $USIZE-1/<8|6, (r1)+
but the actual code from m40.s reads
0636: mov $usize-1\<8|6,(r1)+
However, since < and > where also used to delimit strings, there was a
need to escape them so as to distinguish their usage as shifts from the
string delimiters. The escaping was achieved by \ which is what you see
in the code.
See the assembler section of vol 2b of the Unix V7 manuals for details at
http://plan9.bell-labs.com/7thEdMan/v7vol2b.pdf
or
http://web.cuzuco.com/%7Ecuzuco/v7/v7vol2b.pdf
namely:
6.1 Expression operators
The operators are:
(blank) when there is no operand between operands, the effect is
exactly the same as if a + had appeared.
+ addition
subtraction
* multiplication
\/ division (note that plain / starts a comment)
& bitwise and
| bitwise or
\> logical right shift
\< logical left shift
... ... ...
j
On Mon, 2 Oct 2006 09:44:58 +0300
jigsaw <jigsaw(a)gmail.com> wrote:
> hi all,
>
> I just started to read the source code of V6 with Lion's book.
>
> But before I went far I was stopped by m40.s
>
0636: mov $USIZE-1/<8|6, (r1)+
>
> What does the slash "/" stand for?
>
> I guess this line should be
>
> mov $USIZE-1<<8|6, (r1)+
>
> Is "/<" the same as "<<"?
>
> I checked in Unix PDP11 Assemble Refrence Manual but didn't find a clue.
>
> Is it the right place to ask such question?
>
> Thanks in advance
>
> Regards,
>
> Qinglai
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