From: Markus Armbruster <armbru@redhat.com>
To: qemu-devel@nongnu.org
Cc: peter.maydell@linaro.org
Subject: [PULL 11/33] string-output-visitor: Fix to use sufficient precision
Date: Sat, 19 Dec 2020 11:55:10 +0100 [thread overview]
Message-ID: <20201219105532.1734134-12-armbru@redhat.com> (raw)
In-Reply-To: <20201219105532.1734134-1-armbru@redhat.com>
The string output visitor should serialize numbers so that the string
input visitor deserializes them back to the same number. It fails to
do so.
print_type_number() uses format %f. This is prone to nasty rounding
errors. For instance, numbers between 0 and 0.0000005 get flushed to
zero.
We currently use this visitor only for HMP info migrate, info network,
info qtree, and info memdev. No double values occur there as far as I
can tell.
Fix anyway by formatting with %.17g. 17 decimal digits always suffice
for IEEE double.
See also recent commit "qobject: Fix qnum_to_string() to use
sufficient precision".
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20201210161452.2813491-9-armbru@redhat.com>
---
qapi/string-output-visitor.c | 2 +-
tests/test-string-output-visitor.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/qapi/string-output-visitor.c b/qapi/string-output-visitor.c
index b74aa4d44c..5506c933de 100644
--- a/qapi/string-output-visitor.c
+++ b/qapi/string-output-visitor.c
@@ -258,7 +258,7 @@ static bool print_type_number(Visitor *v, const char *name, double *obj,
Error **errp)
{
StringOutputVisitor *sov = to_sov(v);
- string_output_set(sov, g_strdup_printf("%f", *obj));
+ string_output_set(sov, g_strdup_printf("%.17g", *obj));
return true;
}
diff --git a/tests/test-string-output-visitor.c b/tests/test-string-output-visitor.c
index cec20848ea..0dae04b960 100644
--- a/tests/test-string-output-visitor.c
+++ b/tests/test-string-output-visitor.c
@@ -136,7 +136,7 @@ static void test_visitor_out_number(TestOutputVisitorData *data,
visit_type_number(data->ov, NULL, &value, &error_abort);
str = visitor_get(data);
- g_assert_cmpstr(str, ==, "3.141593");
+ g_assert_cmpstr(str, ==, "3.1415926535897931");
}
static void test_visitor_out_string(TestOutputVisitorData *data,
--
2.26.2
next prev parent reply other threads:[~2020-12-19 11:01 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-19 10:54 [PULL 00/33] QAPI patches patches for 2020-12-19 Markus Armbruster
2020-12-19 10:55 ` [PULL 01/33] rocker: Revamp fp_port_get_info Markus Armbruster
2020-12-19 10:55 ` [PULL 02/33] migration: Refactor migrate_cap_add Markus Armbruster
2020-12-19 10:55 ` [PULL 03/33] qapi: Use QAPI_LIST_PREPEND() where possible Markus Armbruster
2020-12-19 10:55 ` [PULL 04/33] tests/check-qjson: Don't skip funny QNumber to JSON conversions Markus Armbruster
2020-12-19 10:55 ` [PULL 05/33] tests/check-qjson: Examine QNum more thoroughly Markus Armbruster
2020-12-19 10:55 ` [PULL 06/33] tests/check-qjson: Cover number 2^63 Markus Armbruster
2020-12-19 10:55 ` [PULL 07/33] tests/check-qjson: Replace redundant large_number() Markus Armbruster
2020-12-19 10:55 ` [PULL 08/33] tests/check-qnum: Cover qnum_to_string() for "unround" argument Markus Armbruster
2020-12-19 10:55 ` [PULL 09/33] qobject: Fix qnum_to_string() to use sufficient precision Markus Armbruster
2020-12-19 10:55 ` [PULL 10/33] test-string-output-visitor: Cover "unround" number Markus Armbruster
2020-12-19 10:55 ` Markus Armbruster [this message]
2020-12-19 10:55 ` [PULL 12/33] test-visitor-serialization: Drop insufficient precision workaround Markus Armbruster
2020-12-19 10:55 ` [PULL 13/33] test-visitor-serialization: Clean up test_primitives() Markus Armbruster
2020-12-19 10:55 ` [PULL 14/33] hmp: Simplify how qmp_human_monitor_command() gets output Markus Armbruster
2020-12-19 10:55 ` [PULL 15/33] monitor: Use GString instead of QString for output buffer Markus Armbruster
2020-12-19 10:55 ` [PULL 16/33] qobject: Make qobject_to_json_pretty() take a pretty argument Markus Armbruster
2020-12-19 10:55 ` [PULL 17/33] qobject: Use GString instead of QString to accumulate JSON Markus Armbruster
2020-12-19 10:55 ` [PULL 18/33] qobject: Change qobject_to_json()'s value to GString Markus Armbruster
2020-12-19 10:55 ` [PULL 19/33] Revert "qstring: add qstring_free()" Markus Armbruster
2020-12-19 10:55 ` [PULL 20/33] hw/rdma: Replace QList by GQueue Markus Armbruster
2020-12-19 10:55 ` [PULL 21/33] qobject: Move internals to qobject-internal.h Markus Armbruster
2020-12-19 10:55 ` [PULL 22/33] qmp: Fix tracing of non-string command IDs Markus Armbruster
2020-12-19 10:55 ` [PULL 23/33] block: Avoid qobject_get_try_str() Markus Armbruster
2020-12-19 10:55 ` [PULL 24/33] Revert "qobject: let object_property_get_str() use new API" Markus Armbruster
2020-12-19 10:55 ` [PULL 25/33] qobject: Drop qobject_get_try_str() Markus Armbruster
2020-12-19 10:55 ` [PULL 26/33] qobject: Drop qstring_get_try_str() Markus Armbruster
2020-12-19 10:55 ` [PULL 27/33] qobject: Factor quoted_str() out of to_json() Markus Armbruster
2020-12-19 10:55 ` [PULL 28/33] qobject: Factor JSON writer out of qobject_to_json() Markus Armbruster
2020-12-19 10:55 ` [PULL 29/33] migration: Replace migration's JSON writer by the general one Markus Armbruster
2020-12-19 10:55 ` [PULL 30/33] json: Use GString instead of QString to accumulate strings Markus Armbruster
2020-12-19 10:55 ` [PULL 31/33] keyval: Use GString to accumulate value strings Markus Armbruster
2020-12-19 10:55 ` [PULL 32/33] block: Use GString instead of QString to build filenames Markus Armbruster
2020-12-19 10:55 ` [PULL 33/33] qobject: Make QString immutable Markus Armbruster
2020-12-19 11:24 ` [PULL 00/33] QAPI patches patches for 2020-12-19 no-reply
2021-01-01 16:56 ` Peter Maydell
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