Re: bit-extract seems broken.

[Jim Blandy]

Dirk Herrmann <address@hidden> writes:

> On 18 Dec 2000, Rob Browning wrote:
> 
> > 
> >   guile> (bit-extract #b111110100000 0 32)
> >   0
> >   guile>
> > 
> > or can it not return more than a limited range?
> 
> I just wanted to fix it, but realized that it is not really clear to me
> what bit-extract should do with negative numbers.  Opinions?  Should we
> for example only allow non-negative arguments?
> 
> Further, I stumbled across what I think is a gcc compiler error on sparc
> solaris:  x << y or x >> y appears to always give the same results if
> y = a + b*32, no matter what b is.  In other words, the shift operation
> only uses the last 5 bits of the operand.  I assume that this does not
> conform to the C standard?  If anyone can confirm this, I will send a bug
> report.  (Hopefully there's no Klingon programmer responsible for that
> part of the compiler :-)

According to ISO C: "[i]f the value of the right operand [of a shift
operator] is negative or is greater than or equal to the width of the
promoted left operand, the behavior is undefined."

Negative values for the