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From: Daniel Colascione <dancol@dancol.org>
To: Andreas Schwab <schwab@linux-m68k.org>
Cc: Emacs development discussions <emacs-devel@gnu.org>
Subject: Re: Set operations on bool-vectors
Date: Sat, 21 Sep 2013 00:38:43 -0700	[thread overview]
Message-ID: <523D4D03.7010200@dancol.org> (raw)
In-Reply-To: <87a9j6bp90.fsf@igel.home>

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On 9/21/13 12:36 AM, Andreas Schwab wrote:
> Daniel Colascione <dancol@dancol.org> writes:
> 
>> +static
>> +ptrdiff_t
>> +bool_vector_payload_bytes (EMACS_INT length)
>> +{
>> +  EMACS_INT exact_needed_bytes;
>> +  EMACS_INT needed_bytes;
>> +
>> +  exact_needed_bytes = (length + CHAR_BIT - 1) / CHAR_BIT;
>> +  needed_bytes =  (exact_needed_bytes + sizeof (size_t) - 1)
>> +    / sizeof (size_t);
>> +
>> +  needed_bytes *= sizeof (size_t);
> 
> Please check for overflow. 

It can't overflow.  The initial number of bits comes from a Lisp
integer, which has a bit less range than an int.  What exactly is the
routine supposed to do if the value overflows?

> Also, the return type should be EMACS_INT,
> not ptrdiff_t.

Well, vector_nbytes works with ptrdiff_t, and the allocation code works
in EMACS_INT.  I'm not sure the distinction actually matters in this case.


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  reply	other threads:[~2013-09-21  7:38 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-09-20 22:59 Set operations on bool-vectors Daniel Colascione
2013-09-21  1:57 ` Stefan Monnier
2013-09-21  2:44   ` Daniel Colascione
2013-09-21 15:51     ` Stefan Monnier
2013-09-21  2:26 ` Dmitry Antipov
2013-09-21  2:49   ` Daniel Colascione
2013-09-21  7:16     ` Eli Zaretskii
2013-09-21  7:43       ` Daniel Colascione
2013-09-21  7:36 ` Andreas Schwab
2013-09-21  7:38   ` Daniel Colascione [this message]
2013-09-21  8:35     ` Andreas Schwab
2013-09-21  8:49       ` Daniel Colascione

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