[Simh] A few more possible bugs found

[J. David Bryan]

On Tuesday, March 20, 2012 at 18:02, Michael Bloom wrote:

> 5) In pif_io(), in HP2100/hp2100_pif.c
> At the line
>         setIRQ (select_code, !pif_control & pif_flag & pif_flagbuf);
> Is it really intended to use a boolean value with a bitwise operator?

To which boolean value are you referring?  The three "pif" variables are 
enums (compatible with int) with values of 0 or 1, the logical negation 
produces an int, and ANDing produces an int, which is what is desired.

(The hardware modeled is a three-input AND gate with one input inverted.)


> (should ~ have been used instead of !

! produces 0 or 1, which matches one of the enum values.  ~ produces a 
value that is not one of the enum values.

In practice, though, only the LSB matters for setIRQ(), so they'd be 
effectively equivalent.


>  or perhaps parenthesis added to make it clearer?) 

I'm not sure I see where you'd add the parentheses.  Around !pif_control?

                                      -- Dave