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random.tcc (uniform_int_distribution<>::operator()): Fix to work well for arbitrary urng.max() and urng.min().

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2010-06-20  Paolo Carlini  <paolo.carlini@oracle.com>
	    Kai-Uwe Bux  <bux@kubux.net>

	* include/bits/random.tcc (uniform_int_distribution<>::operator()):
	Fix to work well for arbitrary urng.max() and urng.min().

Co-Authored-By: Kai-Uwe Bux <bux@kubux.net>

From-SVN: r161054
This commit is contained in:
Paolo Carlini 2010-06-20 21:03:10 +00:00 • committed by Paolo Carlini
parent 6e2f19568a
commit b7d3d70f77
2 changed files with 57 additions and 17 deletions
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6
libstdc++-v3/ChangeLog
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@ -1,3 +1,9 @@
2010-06-20 Paolo Carlini <paolo.carlini@oracle.com>
Kai-Uwe Bux <bux@kubux.net>
* include/bits/random.tcc (uniform_int_distribution<>::operator()):
Fix to work well for arbitrary urng.max() and urng.min().
2010-06-18 Paolo Carlini <paolo.carlini@oracle.com>
PR libstdc++/32618

68
libstdc++-v3/include/bits/random.tcc
View file

@ -828,27 +828,61 @@ namespace std
operator()(_UniformRandomNumberGenerator& __urng,
const param_type& __param)
{
// XXX Must be fixed to work well for *arbitrary* __urng.max(),
// __urng.min(), __param.b(), __param.a(). Currently works fine only
// in the most common case __urng.max() - __urng.min() >=
// __param.b() - __param.a(), with __urng.max() > __urng.min() >= 0.
typedef typename std::make_unsigned<typename
_UniformRandomNumberGenerator::result_type>::type __urntype;
_UniformRandomNumberGenerator::result_type>::type __urngtype;
typedef typename std::make_unsigned<result_type>::type __utype;
typedef typename std::conditional<(sizeof(__urntype) > sizeof(__utype)),
__urntype, __utype>::type __uctype;
typedef typename std::conditional<(sizeof(__urngtype)
> sizeof(__utype)),
__urngtype, __utype>::type __uctype;
result_type __ret;
const __uctype __urngmin = __urng.min();
const __uctype __urngmax = __urng.max();
const __uctype __urngrange = __urngmax - __urngmin;
const __uctype __urange
= __uctype(__param.b()) - __uctype(__param.a());
const __urntype __urnmin = __urng.min();
const __urntype __urnmax = __urng.max();
const __urntype __urnrange = __urnmax - __urnmin;
const __uctype __urange = __param.b() - __param.a();
const __uctype __udenom = (__urnrange <= __urange
? 1 : __urnrange / (__urange + 1));
do
__ret = (__urntype(__urng()) - __urnmin) / __udenom;
while (__ret > __param.b() - __param.a());
__uctype __ret;
if (__urngrange > __urange)
{
// downscaling
const __uctype __uerange = __urange + 1; // __urange can be zero
const __uctype __scaling = __urngrange / __uerange;
const __uctype __past = __uerange * __scaling;
do
__ret = __uctype(__urng()) - __urngmin;
while (__ret >= __past);
__ret /= __scaling;
}
else if (__urngrange < __urange)
{
// upscaling
/*
Note that every value in [0, urange]
can be written uniquely as
(urngrange + 1) * high + low
where
high in [0, urange / (urngrange + 1)]
and
low in [0, urngrange].
*/
__uctype __tmp; // wraparound control
do
{
const __uctype __uerngrange = __urngrange + 1;
__tmp = (__uerngrange * operator()
(__urng, param_type(0, __urange / __uerngrange)));
__ret = __tmp + (__uctype(__urng()) - __urngmin);
}
while (__ret > __urange || __ret < __tmp);
}
else
__ret = __uctype(__urng()) - __urngmin;
return __ret + __param.a();
}