Re: [PATCH] Clear upper bits during sign extension

[Yao Qi <yao@codesourcery.com>]

Joel Brobecker <brobecker@adacore.com> writes:

> 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...

Yeah, that is better, or even we can left shift signbit by one.

-- 
Yao (齐尧)

gdb:

2014-12-29  Yao Qi  <yao@codesourcery.com>

        * utils.c (gdb_sign_extend): Clear bits from BIT in VALUE.

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;
     }