http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50509
Bug #: 50509
Summary: incorrect code in std::seed_seq::generate
Classification: Unclassified
Product: gcc
Version: 4.6.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: john.sal...@deshaw.com
The implementation of std::seed_seq::generate contains two typos. The code
uses '<<' where the standard in rand.util.seed_seq 26.5.7.1 paragraph 8 says:
T(x) is defined as x xor (x rshift 27)
Here's a patch against the 4.6.1 tree:
salm...@drdlogin0039.en.desres$ diff -u
/proj/desres/root/Linux/x86_64/gcc/4.6.1-23A/include/c++/4.6.1/bits/random.tcc
myrandom/bits/random.tcc
---
/proj/desres/root/Linux/x86_64/gcc/4.6.1-23A/include/c++/4.6.1/bits/random.tcc
2011-06-27 15:29:53.000000000 -0400
+++ myrandom/bits/random.tcc 2011-09-19 10:04:46.836512000 -0400
@@ -2768,7 +2768,7 @@
_Type __arg = (__begin[__k % __n]
^ __begin[(__k + __p) % __n]
^ __begin[(__k - 1) % __n]);
- _Type __r1 = __arg ^ (__arg << 27);
+ _Type __r1 = __arg ^ (__arg >> 27);
__r1 = __detail::__mod<_Type, __detail::_Shift<_Type, 32>::__value,
1664525u, 0u>(__r1);
_Type __r2 = __r1;
@@ -2790,7 +2790,7 @@
_Type __arg = (__begin[__k % __n]
+ __begin[(__k + __p) % __n]
+ __begin[(__k - 1) % __n]);
- _Type __r3 = __arg ^ (__arg << 27);
+ _Type __r3 = __arg ^ (__arg >> 27);
__r3 = __detail::__mod<_Type, __detail::_Shift<_Type, 32>::__value,
1566083941u, 0u>(__r3);
_Type __r4 = __r3 - __k % __n;
salm...@drdlogin0039.en.desres$
