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Message-ID: <20160904025102.GN1280@port70.net>
Date: Sun, 4 Sep 2016 04:51:03 +0200
From: Szabolcs Nagy <nsz@...t70.net>
To: musl@...ts.openwall.com
Subject: [PATCH][RFC] fix strtod int optimization in non-nearest rounding mode
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
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