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[PATCH 08/10] string-output-visitor: Fix to use sufficient precision
From: |
Markus Armbruster |
Subject: |
[PATCH 08/10] string-output-visitor: Fix to use sufficient precision |
Date: |
Thu, 10 Dec 2020 17:14:50 +0100 |
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>
---
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
- [PATCH 00/10] Fix floating-point -> text conversion precision, Markus Armbruster, 2020/12/10
- [PATCH 09/10] test-visitor-serialization: Drop insufficient precision workaround, Markus Armbruster, 2020/12/10
- [PATCH 05/10] tests/check-qnum: Cover qnum_to_string() for "unround" argument, Markus Armbruster, 2020/12/10
- [PATCH 03/10] tests/check-qjson: Cover number 2^63, Markus Armbruster, 2020/12/10
- [PATCH 07/10] test-string-output-visitor: Cover "unround" number, Markus Armbruster, 2020/12/10
- [PATCH 02/10] tests/check-qjson: Examine QNum more thoroughly, Markus Armbruster, 2020/12/10
- [PATCH 01/10] tests/check-qjson: Don't skip funny QNumber to JSON conversions, Markus Armbruster, 2020/12/10
- [PATCH 04/10] tests/check-qjson: Replace redundant large_number(), Markus Armbruster, 2020/12/10
- [PATCH 10/10] test-visitor-serialization: Clean up test_primitives(), Markus Armbruster, 2020/12/10
- [PATCH 08/10] string-output-visitor: Fix to use sufficient precision,
Markus Armbruster <=
- [PATCH 06/10] qobject: Fix qnum_to_string() to use sufficient precision, Markus Armbruster, 2020/12/10
- Re: [PATCH 00/10] Fix floating-point -> text conversion precision, no-reply, 2020/12/10