From: Szabolcs Nagy <nsz@port70.net>
To: musl@lists.openwall.com
Subject: [PATCH][RFC] fix strtod int optimization in non-nearest rounding mode
Date: Sun, 4 Sep 2016 04:51:03 +0200 [thread overview]
Message-ID: <20160904025102.GN1280@port70.net> (raw)
the mid-sized integer optimization relies on lnz set up properly
to mark the last non-zero decimal digit, but this was not done
if the non-zero digit lied outside the KMAX digits of the base
10^9 number representation.
so if the fractional part was a very long list of zeros (>2048*9 on
x86) followed by non-zero digits then the integer optimization could
kick in discarding the tiny non-zero fraction which can mean wrong
result on non-nearest rounding mode.
strtof, strtod and strtold were all affected.
---
the dc counter is long long, but lnz is int, so this is
not correct on 64bit targets where dc can be >INT_MAX,
probably lnz should be just set to KMAX*9 or similar in
this case.
src/internal/floatscan.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/src/internal/floatscan.c b/src/internal/floatscan.c
index 66d01ef..682b80a 100644
--- a/src/internal/floatscan.c
+++ b/src/internal/floatscan.c
@@ -110,7 +110,10 @@ static long double decfloat(FILE *f, int c, int bits, int emin, int sign, int po
gotdig=1;
} else {
dc++;
- if (c!='0') x[KMAX-4] |= 1;
+ if (c!='0') {
+ lnz = dc;
+ x[KMAX-4] |= 1;
+ }
}
}
if (!gotrad) lrp=dc;
--
2.9.3
next reply other threads:[~2016-09-04 2:51 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-04 2:51 Szabolcs Nagy [this message]
2016-09-09 23:55 ` Rich Felker
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20160904025102.GN1280@port70.net \
--to=nsz@port70.net \
--cc=musl@lists.openwall.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://git.vuxu.org/mirror/musl/
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).