===================================================================
@@ -828,28 +828,62 @@
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();
}