Struct std.random.XorshiftEngine
Xorshift generator. Implemented according to Xorshift RNGs (Marsaglia, 2003) when the size is small. For larger sizes the generator uses Sebastino Vigna's optimization of using an index to avoid needing to rotate the internal array.
struct XorshiftEngine(UIntType, uint nbits, int sa, int sb, int sc)
if (isUnsigned!UIntType && !(sa > 0 && (sb > 0) && (sc > 0)));
alias XorshiftEngine(UIntType, int bits, int a, int b, int c)
= XorshiftEngine!(UIntType,bits,a,-b,c);
Period is 2 ^^ nbits - 1 except for a legacy 192-bit uint version (see
note below).
Struct XorshiftEngine
Constructors
| Name | Description |
|---|---|
this
(x0)
|
Constructs a XorshiftEngine generator seeded with x0.
|
Properties
| Name | Type | Description |
|---|---|---|
front[get]
|
UIntType | Returns the current number in the random sequence. |
save[get]
|
typeof(this) | Captures a range state. |
Methods
| Name | Description |
|---|---|
popFront
()
|
Advances the random sequence. |
seed
(x0)
|
(Re)seeds the generator. |
Alias XorshiftEngine
Parameters
| Name | Description |
|---|---|
| UIntType | Word size of this xorshift generator and the return type
of opCall. |
| nbits | The number of bits of state of this generator. This must be a positive multiple of the size in bits of UIntType. If nbits is large this struct may occupy slightly more memory than this so it can use a circular counter instead of shifting the entire array. |
| sa | The direction and magnitude of the 1st shift. Positive means left, negative means right. |
| sb | The direction and magnitude of the 2nd shift. Positive means left, negative means right. |
| sc | The direction and magnitude of the 3rd shift. Positive means left, negative means right. |
Note
For historical compatibility when nbits == 192 and UIntType is uint
a legacy hybrid PRNG is used consisting of a 160-bit xorshift combined
with a 32-bit counter. This combined generator has period equal to the
least common multiple of 2^^160 - 1 and 2^^32.
Previous versions of XorshiftEngine did not provide any mechanism to specify
the directions of the shifts, taking each shift as an unsigned magnitude.
For backwards compatibility, because three shifts in the same direction
cannot result in a full-period XorshiftEngine, when all three of sa, sb,
sc, are positive XorshiftEngine` treats them as unsigned magnitudes and
uses shift directions to match the old behavior of XorshiftEngine.
Not every set of shifts results in a full-period xorshift generator. The template does not currently at compile-time perform a full check for maximum period but in a future version might reject parameters resulting in shorter periods.
Example
alias Xorshift96 = XorshiftEngine!(uint, 96, 10, 5, 26);
auto rnd = Xorshift96(42);
auto num = rndAuthors
Andrei Alexandrescu Masahiro Nakagawa (Xorshift random generator) Joseph Rushton Wakeling (Algorithm D for random sampling) Ilya Yaroshenko (Mersenne Twister implementation, adapted from mir-random)