Re: Question: Checking register value in buffer

[Joel Brobecker <brobecker@adacore.com>]

> > In terms of computing the mask, I'm thinking of using something
> > like this:
> > 
> >   sign_mask = 1 << (sizeof (rav) * TARGET_CHAR_BIT - 1);
> 
> This confuses host and target notions.  You would have wanted
> the *host* CHAR_BIT, since you're using the host sizeof.

Ah yes, of course.

> >   zero_mask = sign_mask ^ -1;
> 
> This fails if rav is *wider* than 64-bits.
> 
> > Are there better ways of computing these masks?
> 
> How about just 
> 
>   sign = (LONGEST)1 << 63
>   zero = sign - 1;

Isn't this assument that LONGEST is exactly 64 bits? I think
extract_signed_integer expands the value held in the given buffer
to fit the size of LONGEST. Here is the implementation:

    LONGEST
    extract_signed_integer (const void *addr, int len)
    {
      LONGEST retval;
      const unsigned char *p;
      const unsigned char *startaddr = addr;
      const unsigned char *endaddr = startaddr + len;
    
      if (len > (int) sizeof (LONGEST))
        error (_("\
    That operation is not available on integers of more than %d bytes."),
               (int) sizeof (LONGEST));
    
      /* Start at the most significant end of the integer, and work towards
         the least significant.  */
      if (TARGET_BYTE_ORDER == BFD_ENDIAN_BIG)
        {
          p = startaddr;
          /* Do the sign extension once at the start.  */
          retval = ((LONGEST) * p ^ 0x80) - 0x80;
          for (++p; p < endaddr; ++p)
            retval = (retval << 8) | *p;
        }
      else
        {
          p = endaddr - 1;
          /* Do the sign extension once at the start.  */
          retval = ((LONGEST) * p ^ 0x80) - 0x80;
          for (--p; p >= startaddr; --p)
            retval = (retval << 8) | *p;
        }
      return retval;
    }

Using an example where we have len = 1 and sizeof LONGEST = 2, then
the extract from "0xff" would lead to "0xffff", no?

That's why I thought the little dance with sizeof and xor was necessary.

-- 
Joel