[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Qemu-devel] [PATCH v10 01/25] qobject: Document more shortcomings in ou
From: |
Eric Blake |
Subject: |
[Qemu-devel] [PATCH v10 01/25] qobject: Document more shortcomings in our number handling |
Date: |
Fri, 29 Jan 2016 06:48:37 -0700 |
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 <address@hidden>
---
v10: comment improvements, drop Marc-Andre's R-b.
v9: no change
v8: no change
v7: new patch
---
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 3c5d35d..95bb054 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 a3e6a7c..8bc7f20 100644
--- a/qobject/qjson.c
+++ b/qobject/qjson.c
@@ -237,6 +237,15 @@ 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--;
@@ -247,7 +256,7 @@ static void to_json(const QObject *obj, QString *str, int
pretty, int indent)
} else {
buffer[len] = 0;
}
-
+
qstring_append(str, buffer);
break;
}
--
2.5.0
- [Qemu-devel] [PATCH v10 00/25] qapi visitor cleanups part 1 (post-introspection cleanups subset E), Eric Blake, 2016/01/29
- [Qemu-devel] [PATCH v10 04/25] qapi: Dealloc visitor does not need a type_size(), Eric Blake, 2016/01/29
- [Qemu-devel] [PATCH v10 07/25] hmp: Cache use of qapi visitor, Eric Blake, 2016/01/29
- [Qemu-devel] [PATCH v10 01/25] qobject: Document more shortcomings in our number handling,
Eric Blake <=
- [Qemu-devel] [PATCH v10 05/25] qapi: Drop dead parameter in gen_params(), Eric Blake, 2016/01/29
- [Qemu-devel] [PATCH v10 08/25] vl: Ensure qapi visitor properly ends struct visit, Eric Blake, 2016/01/29
- [Qemu-devel] [PATCH v10 11/25] qapi: Track all failures between visit_start/stop, Eric Blake, 2016/01/29
- [Qemu-devel] [PATCH v10 03/25] qapi: Drop dead dealloc visitor variable, Eric Blake, 2016/01/29
- [Qemu-devel] [PATCH v10 13/25] qapi: Prefer type_int64 over type_int in visitors, Eric Blake, 2016/01/29
- [Qemu-devel] [PATCH v10 14/25] qapi: Make all visitors supply uint64 callbacks, Eric Blake, 2016/01/29
- [Qemu-devel] [PATCH v10 06/25] hmp: Drop pointless allocation during qapi visit, Eric Blake, 2016/01/29
- [Qemu-devel] [PATCH v10 09/25] balloon: Improve use of qapi visitor, Eric Blake, 2016/01/29
- [Qemu-devel] [PATCH v10 16/25] qapi: Don't cast Enum* to int*, Eric Blake, 2016/01/29
- [Qemu-devel] [PATCH v10 02/25] qapi: Avoid use of misnamed DO_UPCAST(), Eric Blake, 2016/01/29