Re: [PATCH] Clear upper bits during sign extension

[Joel Brobecker <brobecker@adacore.com>]

> 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