On 03/12/2017 05:23 PM, Gerald Pfeifer wrote:
Hi Martin,
On Mon, 27 Feb 2017, Martin Sebor wrote:
Sorry to be jumping in so late. I only noticed this bit now.
I would suggest to say that these new built-ins evaluate to integer
constant expressions when their arguments do. Not all C programmers
are familiar with C++ constexpr so they may not understand the use
use case. The request for these built-ins also came from a C user
and was specifically motivated by avoiding -Woverflow warnings so
adding an example demonstrating that might be helpful as well.
Something like this:
... Calls to these built-ins with integer constant arguments
evaluate to integer constants expressions.</p>
<p>For example, in the following, <code>c</code> is assigned
the result of <code>a * b</code> only if the multiplication
does not overflow, otherwise it is assigned the value zero.
The multiplication is performed at compile-time and without
triggering a <code>-Woverflow</code> warning.
</p>
<blockquote>
<pre>enum {
a = 12345678,
b = 87654321,
c = __builtin_mul_overflow_p (a, b, a) ? 0 : a * b
};</pre>
</blockquote></li>
this works for me, modulo the closing </p> which I believe will be
necessary. Were you seeing approval for this from someone? (If so,
that may not have been me. ;-)
Thanks. I just committed it.
Martin
