An independent_bits_engine random number engine adaptor combines random numbers that are produced by some base engine e, so as to produce random numbers with a specified number of bits w. The state xi of an independent_bits_engine engine adaptor object x consists of the state ei of its base engine e; the size of the state is the size of e's state.
The transition and generation algorithms are described in terms of the following integral constants:
a)Let R=e.max() - e.min() + 1 and m=⌊log2R⌋.
b)With n as determined below, let w0=⌊w/n⌋, n0=n−wmodn, y0=2w0⌊R/2w0⌋, and y1=2w0+1⌊R/2w0+1⌋.
c)Let n=⌈w/m⌉ if and only if the relation R−y0≤⌊y0/n⌋ holds as a result. Otherwise let n=1+⌈w/m⌉.
[ Note: The relation w=n0w0+(n−n0)(w0+1) always holds. — end note ]
The transition algorithm is carried out by invoking e() as often as needed to obtain n0 values less than y0+e.min() and n−n0 values less than y1+e.min().
The generation algorithm uses the values produced while advancing the state as described above to yield a quantity S obtained as if by the following algorithm:
S = 0;
for (k = 0; k≠n0; k += 1) {
do u = e() - e.min(); while (u≥y0);
S = 2w0⋅S+umod2w0;
}
for (k = n0; k≠n; k += 1) {
do u = e() - e.min(); while (u≥y1);
S = 2w0+1⋅S+umod2w0+1;
}
template<class Engine, size_t w, class UIntType>
class independent_bits_engine {
public:
using result_type = UIntType;
static constexpr result_type min() { return 0; }
static constexpr result_type max() { return 2w−1; }
independent_bits_engine();
explicit independent_bits_engine(const Engine& e);
explicit independent_bits_engine(Engine&& e);
explicit independent_bits_engine(result_type s);
template<class Sseq> explicit independent_bits_engine(Sseq& q);
void seed();
void seed(result_type s);
template<class Sseq> void seed(Sseq& q);
result_type operator()();
void discard(unsigned long long z);
const Engine& base() const noexcept { return e; };
private:
Engine e; };
The following relations shall hold: 0 < w and w <= numeric_limits<result_type>::digits.
The textual representation consists of the textual representation of e.
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