lib/44741: strtod convert 0.010000000000000000057612911342378542997169 incorrectly

[alnsn%yandex.ru@localhost]

>Number:         44741
>Category:       lib
>Synopsis:       strtod convert 0.010000000000000000057612911342378542997169 
>incorrectly
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    lib-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Mar 19 00:25:01 +0000 2011
>Originator:     Alexander Nasonov
>Release:        NetBSD 5.99.48 amd64
>Organization:
home sweet home
>Environment:
NetBSD nebeda.localdomain 5.99.48 NetBSD 5.99.48 (GENERIC) #0: Wed Mar 16 
22:33:54 GMT 2011  
root@nebeda.localdomain:/home/alnsn/src/netbsd-current/src/sys/arch/amd64/compile/obj/GENERIC
 amd64

>Description:
See the entry "Fri Nov  5 13:02:41 MDT 2010" from
http://www.netlib.org/fp/changes

Fri Nov  5 13:02:41 MDT 2010
  dtoa.c:  fix a bug related to bigcomp:  decimal strings with all
zeros before the decimal point more than 40 significant digits that
required use of bigcomp might be converted very incorrectly.
Example: .010000000000000000057612911342378542997169 .
Thanks to Rick Regan <exploringbinary%gmail.com@localhost> for reporting the
symptoms and providing an example.
>How-To-Repeat:
Apply the patch to tests/lib/libc/stdlib/t_strtox.c abd run the test.

$ ./t_strtox bug20101105
*** Check failed: 
/home/alnsn/src/netbsd-current/src/tests/lib/libc/stdlib/t_strtox.c:82: buf != 
str (0.010000000000000000208166817117216851329431 != 
0.010000000000000000057612911342378542997169)
failed: 1 checks failed; see output for more details

I don't know whether netbsd guarantees that string->double->string
conversion returns original value so feel free to change
ATF_CHECK_STREQ check to a more correct check.

$ cvs diff -u tests/lib/libc/stdlib/t_strtox.c
Index: tests/lib/libc/stdlib/t_strtox.c
===================================================================
RCS file: /cvsroot/src/tests/lib/libc/stdlib/t_strtox.c,v
retrieving revision 1.2
diff -u -u -r1.2 t_strtox.c
--- tests/lib/libc/stdlib/t_strtox.c    6 Dec 2010 17:30:07 -0000       1.2
+++ tests/lib/libc/stdlib/t_strtox.c    19 Mar 2011 00:01:51 -0000
@@ -32,7 +32,9 @@
 __RCSID("$NetBSD: t_strtox.c,v 1.2 2010/12/06 17:30:07 pooka Exp $");

 #include <atf-c.h>
+#include <stdio.h>
 #include <stdlib.h>
+#include <string.h>

 ATF_TC(hexadecimal);

@@ -56,9 +58,34 @@
        atf_tc_expect_pass();
 }

+ATF_TC(bug20101105);
+
+ATF_TC_HEAD(bug20101105, tc)
+{
+       atf_tc_set_md_var(tc, "descr",
+           "Test strtod(\"0.010000000000000000057612911342378542997169\", 
NULL)");
+}
+
+ATF_TC_BODY(bug20101105, tc)
+{
+       const char str[] = "0.010000000000000000057612911342378542997169";
+       const int digits = sizeof(str) - sizeof("0."); /* precision for %.*f */
+
+       int n;
+       char buf[sizeof(str)];
+
+       double val = strtod(str, NULL);
+
+       n = snprintf(buf, sizeof(buf), "%.*f", digits, val);
+       ATF_REQUIRE(n + 1 == sizeof(buf));
+
+       ATF_CHECK_STREQ(buf, str);
+}
+
 ATF_TP_ADD_TCS(tp)
 {
        ATF_TP_ADD_TC(tp, hexadecimal);
+       ATF_TP_ADD_TC(tp, bug20101105);

        return atf_no_error();
 }
>Fix: