From: Paul Eggert <eggert@cs.ucla.edu>
To: "Jan Djärv" <jan.h.d@swipnet.se>
Cc: 18303@debbugs.gnu.org
Subject: bug#18303: Drag and Drop fails when Emacs window/frame is above top
Date: Mon, 08 Sep 2014 06:10:31 -0700 [thread overview]
Message-ID: <540DAAC7.7040602@cs.ucla.edu> (raw)
In-Reply-To: <A25FEC68-12A3-4830-9F8E-FCBF8D3CB4CA@swipnet.se>
Jan Djärv wrote:
> Thanks, but it does not look right. We can assume v1 and v2 are 16 bit signed integers (X coordinates). In general, when data is a CONS, it must be two 16 bit numbers.
> So (v1 << 16) | v2 is just a way of stuffing two signed 16 bits into 32 bits.
> But when v2 is long, (v2 & 0xffff) looses the sign bit, as the code is now.
I don't see how the expression could keep the sign bit and still work.
Suppose v1 == 27 and v2 == -1. Then ((v1 << 16) | v2) == -1, and we've
lost all information about v1's value. In contrast, ((v1 << 16) | (v2 &
0xffff) == 1835007 == 0x1bffff, so we still can retrieve information
about v1's value by shifting this value right by 16 bits.
> I don't know why the range X_LONG_(MIN|MAX) >> 16 is relevant here, it is way too large.
> Remember, val can only be 32 bit, so X_LONG_MAX >> 16 can in it self be 48 bits.
X_LONG_MAX and X_LONG_MIN are always 32-bit values, even on platforms
where long is 64 bits. So the range X_LONG_MIN >> 16 .. X_LONG_MAX >>
16 is -32768 .. 32767 which should be the correct range for X.
next prev parent reply other threads:[~2014-09-08 13:10 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-20 12:50 bug#18303: Drag and Drop fails when Emacs window/frame is above top Paulie Pena IV
2014-09-07 17:32 ` Jan Djärv
2014-09-07 19:50 ` Paul Eggert
2014-09-08 5:04 ` Jan Djärv
2014-09-08 13:10 ` Paul Eggert [this message]
2014-09-08 15:18 ` Jan Djärv
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