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Re: [PATCH] Clear upper bits during sign extension
- From: Joel Brobecker <brobecker at adacore dot com>
- To: Yao Qi <yao at codesourcery dot com>
- Cc: gdb-patches at sourceware dot org
- Date: Mon, 29 Dec 2014 07:06:59 +0400
- Subject: Re: [PATCH] Clear upper bits during sign extension
- Authentication-results: sourceware.org; auth=none
- References: <1419815569-21854-1-git-send-email-yao at codesourcery dot 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