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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 07:53:19 +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> <20141229030659 dot GB2123 at adacore dot com> <87d273w2gl dot fsf at codesourcery dot com>
> Yeah, that is better, or even we can left shift signbit by one.
Indeed!
> 2014-12-29 Yao Qi <yao@codesourcery.com>
>
> * utils.c (gdb_sign_extend): Clear bits from BIT in VALUE.
Looks good to me.
> diff --git a/gdb/utils.c b/gdb/utils.c
> index 47adb67..61873f7 100644
> --- a/gdb/utils.c
> +++ b/gdb/utils.c
> @@ -3032,6 +3032,9 @@ gdb_sign_extend (LONGEST value, int bit)
> {
> LONGEST signbit = ((LONGEST) 1) << (bit - 1);
>
> + /* Clear upper bits from bit BIT. */
> + value &= (signbit << 1) - 1;
> +
> value = (value ^ signbit) - signbit;
> }
--
Joel