From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 30868 invoked by alias); 20 Sep 2016 16:57:10 -0000 Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org Received: (qmail 30777 invoked by uid 89); 20 Sep 2016 16:57:09 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-4.0 required=5.0 tests=BAYES_00,KAM_LAZY_DOMAIN_SECURITY,RP_MATCHES_RCVD,SPF_HELO_PASS autolearn=ham version=3.3.2 spammy=ooc, OOC X-HELO: mx1.redhat.com Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Tue, 20 Sep 2016 16:57:07 +0000 Received: from int-mx11.intmail.prod.int.phx2.redhat.com (int-mx11.intmail.prod.int.phx2.redhat.com [10.5.11.24]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 74D4C8AE72 for ; Tue, 20 Sep 2016 16:57:06 +0000 (UTC) Received: from [127.0.0.1] (ovpn01.gateway.prod.ext.ams2.redhat.com [10.39.146.11]) by int-mx11.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id u8KGv58t002007; Tue, 20 Sep 2016 12:57:05 -0400 Subject: Re: [PATCH] Implement floordiv operator for gdb.Value To: Jonathan Wakely References: <20160920132633.GA897@redhat.com> <883c76d5-54e9-e8fe-5713-eec2c4010498@redhat.com> <20160920163556.GB5736@redhat.com> Cc: gdb-patches@sourceware.org From: Pedro Alves Message-ID: Date: Tue, 20 Sep 2016 17:01:00 -0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 MIME-Version: 1.0 In-Reply-To: <20160920163556.GB5736@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-SW-Source: 2016-09/txt/msg00232.txt.bz2 On 09/20/2016 05:35 PM, Jonathan Wakely wrote: > On 20/09/16 16:33 +0100, Pedro Alves wrote: >> Hi there, >> >> Thanks! >> >> On 09/20/2016 02:26 PM, Jonathan Wakely wrote: >>> This is my attempt to implement the // operator on gdb.Value objects. >>> There is already BINOP_INTDIV which works fine for integral types, but >>> for floats I use BINOP_DIV and then call floor() on the result. This >>> doesn't support decimal floats though. >>> >>> Is this a reasonable solution? Is the test sufficient? >>> >> >> See below. >> >>> @@ -1142,7 +1160,15 @@ valpy_binop_throw (enum valpy_opcode opcode, >>> PyObject *self, PyObject *other) >>> } >>> >>> if (res_val) >>> - result = value_to_value_object (res_val); >>> + { >>> + if (floor_it) >>> + { >>> + double d = value_as_double (res_val); >> >> Should be s/double/DOUBLEST, I suppose? > > OK - if I do that then floor(d) will convert it back to double, > unless you #include and using std::floor, so that the overload > for long double is visible (in C++ names like floor are > overloaded so you don't need to use floorf/floor/floorl according to > the type). OK. I remember reading your blog about this mess a while ago. If easy to do, sounds like we should just do it. OOC, would calling std::floor directly instead of using "using" work just as well? (This kind of raises the question of which float type / format / representation to use for arithmetic here -- host's or target's. gdb currently always uses host's, but that's a much larger issue that we can just continue to ignore.) >> Is the "two double values" test returning an integer somehow? >> >> I ask because IIUC, regardless of Python version, a floor-divide >> involving a float should result in a float, while a floor-divide of >> integers should result in an integer. And that's what the patch looks >> like should end up with. So I was expecting to see "0.0" in >> the "two double values" case: >> >> (gdb) python print (5.0//6.0) >> 0.0 >> (gdb) python print (5//6) >> 0 > > This seems to be an existing property of gdb.Value, as even using the > normal division operator (and without my patch) I see floats printed > without a decimal part when they are an integer value: > > (gdb) python print (gdb.Value(5.0)/5.0) > 1 > (gdb) python print (5.0/5.0) > 1.0 Curious. Off hand looks like a bug to me. But since it's orthogonal to your patch, let's leave it. >> I think it'd be good to test with negative numbers too, to make >> sure that we round (and keep rounding) toward the same >> direction Python rounds: >> >> (gdb) python print (8.0//-3) >> -3.0 >> (gdb) python print (8//-3) >> -3 >> (gdb) print 8/-3 >> $1 = -2 > > Good point, I'll do that. Thanks, Pedro Alves