From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34217) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aT6cW-0007rq-JB for qemu-devel@nongnu.org; Tue, 09 Feb 2016 06:38:13 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aT6cS-0002yW-AV for qemu-devel@nongnu.org; Tue, 09 Feb 2016 06:38:12 -0500 Received: from mx1.redhat.com ([209.132.183.28]:37515) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aT6cS-0002yE-52 for qemu-devel@nongnu.org; Tue, 09 Feb 2016 06:38:08 -0500 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) by mx1.redhat.com (Postfix) with ESMTPS id C6F348F4F5 for ; Tue, 9 Feb 2016 11:38:07 +0000 (UTC) From: Markus Armbruster Date: Tue, 9 Feb 2016 12:37:37 +0100 Message-Id: <1455017883-25867-6-git-send-email-armbru@redhat.com> In-Reply-To: <1455017883-25867-1-git-send-email-armbru@redhat.com> References: <1455017883-25867-1-git-send-email-armbru@redhat.com> Subject: [Qemu-devel] [PULL 05/31] qobject: Document more shortcomings in our number handling List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org From: Eric Blake We've already documented that our JSON parsing is locale dependent; but we should also document that our JSON output has the same problem. Additionally, JSON requires finite values (you have to upgrade to JSON5 to get support for Inf or NaN), and our output truncates floating point numbers to the point of losing significant precision that could cause the receiver to read a different value. Sadly, this series is not going to be the one that addresses these problems. Fix some trailing whitespace I noticed in the vicinity. Signed-off-by: Eric Blake Message-Id: <1454075341-13658-2-git-send-email-eblake@redhat.com> Signed-off-by: Markus Armbruster --- qobject/json-parser.c | 6 ++++-- qobject/qjson.c | 11 ++++++++++- 2 files changed, 14 insertions(+), 3 deletions(-) diff --git a/qobject/json-parser.c b/qobject/json-parser.c index 77c9382..6c05f6c 100644 --- a/qobject/json-parser.c +++ b/qobject/json-parser.c @@ -1,5 +1,5 @@ /* - * JSON Parser + * JSON Parser * * Copyright IBM, Corp. 2009 * @@ -518,7 +518,9 @@ static QObject *parse_literal(JSONParserContext *ctxt) /* fall through to JSON_FLOAT */ } case JSON_FLOAT: - /* FIXME dependent on locale */ + /* FIXME dependent on locale; a pervasive issue in QEMU */ + /* FIXME our lexer matches RFC 7159 in forbidding Inf or NaN, + * but those might be useful extensions beyond JSON */ return QOBJECT(qfloat_from_double(strtod(token->str, NULL))); default: abort(); diff --git a/qobject/qjson.c b/qobject/qjson.c index b8cc4ca..06dc210 100644 --- a/qobject/qjson.c +++ b/qobject/qjson.c @@ -238,6 +238,15 @@ static void to_json(const QObject *obj, QString *str, int pretty, int indent) char buffer[1024]; int len; + /* FIXME: snprintf() is locale dependent; but JSON requires + * numbers to be formatted as if in the C locale. Dependence + * on C locale is a pervasive issue in QEMU. */ + /* FIXME: This risks printing Inf or NaN, which are not valid + * JSON values. */ + /* FIXME: the default precision of 6 for %f often causes + * rounding errors; we should be using DBL_DECIMAL_DIG (17), + * and only rounding to a shorter number if the result would + * still produce the same floating point value. */ len = snprintf(buffer, sizeof(buffer), "%f", qfloat_get_double(val)); while (len > 0 && buffer[len - 1] == '0') { len--; @@ -248,7 +257,7 @@ static void to_json(const QObject *obj, QString *str, int pretty, int indent) } else { buffer[len] = 0; } - + qstring_append(str, buffer); break; } -- 2.4.3