[−][src]Struct rand_core::block::BlockRng

A wrapper type implementing RngCore for some type implementing BlockRngCore with u32 array buffer; i.e. this can be used to implement a full RNG from just a generate function.

The core field may be accessed directly but the results buffer may not. PRNG implementations can simply use a type alias (pub type MyRng = BlockRng<MyRngCore>;) but might prefer to use a wrapper type (pub struct MyRng(BlockRng<MyRngCore>);); the latter must re-implement RngCore but hides the implementation details and allows extra functionality to be defined on the RNG (e.g. impl MyRng { fn set_stream(...){...} }).

BlockRng has heavily optimized implementations of the RngCore methods reading values from the results buffer, as well as calling BlockRngCore::generate directly on the output array when fill_bytes / try_fill_bytes is called on a large array. These methods also handle the bookkeeping of when to generate a new batch of values.

No whole generated u32 values are thown away and all values are consumed in-order. next_u32 simply takes the next available u32 value. next_u64 is implemented by combining two u32 values, least significant first. fill_bytes and try_fill_bytes consume a whole number of u32 values, converting each u32 to a byte slice in little-endian order. If the requested byte length is not a multiple of 4, some bytes will be discarded.

See also BlockRng64 which uses u64 array buffers. Currently there is no direct support for other buffer types.

For easy initialization BlockRng also implements SeedableRng.

The core part of the RNG, implementing the generate function.