[PATCH] PR libstdc++/80506 fix constant used in condition

[Jonathan Wakely]

We use the wrong constant for the Marsaglia Tsang algorithm.

        PR libstdc++/80506
        * include/bits/random.tcc (gamma_distribution::operator()): Fix magic
        number used in loop condition.

Tested powerpc64le-linux, committed to trunk.



commit aa4da6523b7bfab7ba92c2e9e505155e1ce432a7
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Mon Apr 24 13:10:49 2017 +0100

    PR libstdc++/80506 fix constant used in condition
    
        PR libstdc++/80506
        * include/bits/random.tcc (gamma_distribution::operator()): Fix magic
        number used in loop condition.

diff --git a/libstdc++-v3/include/bits/random.tcc 
b/libstdc++-v3/include/bits/random.tcc
index df05ebe..63d1c02 100644
--- a/libstdc++-v3/include/bits/random.tcc
+++ b/libstdc++-v3/include/bits/random.tcc
@@ -2356,7 +2356,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
            __v = __v * __v * __v;
            __u = __aurng();
          }
-       while (__u > result_type(1.0) - 0.331 * __n * __n * __n * __n
+       while (__u > result_type(1.0) - 0.0331 * __n * __n * __n * __n
               && (std::log(__u) > (0.5 * __n * __n + __a1
                                    * (1.0 - __v + std::log(__v)))));