Re: [PATCH] Clear upper bits during sign extension

Joel Brobecker
2014-12-29T03:07:10Z

> 2014-12-29 Yao Qi <yao@codesourcery.com>
>
> * utils.c (gdb_sign_extend): Clear bits from BIT in VALUE.
> ---
> gdb/utils.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/gdb/utils.c b/gdb/utils.c
> index 47adb67..e029863 100644
> --- a/gdb/utils.c
> +++ b/gdb/utils.c
> @@ -3031,6 +3031,15 @@ gdb_sign_extend (LONGEST value, int bit)
> if (((value >> (bit - 1)) & 1) != 0)
> {
> LONGEST signbit = ((LONGEST) 1) << (bit - 1);
> + LONGEST mask = 1;
> + int i;
> +
> + /* Generate a mask in which bits [0, BIT - 1] are one. */
> + for (i = 0; i < bit; i++)
> + mask = mask << 1;
> + mask--;
> + /* Clear bits from bit BIT. */
> + value &= mask;

I think you can simplify the above with just:

value &= ((LONGEST) 1 << bit) - 1;

? I don't know if the cast to LONGEST is really necessary, but we use
it for signbit, so I did the same for the mask...

--
Joel