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BNNSRandomGeneratorGetState(_:_:_:)

Returns the state of a random number generator.

Declaration

func BNNSRandomGeneratorGetState(_ generator: BNNSRandomGenerator?, _ state_size: Int, _ state: UnsafeMutableRawPointer) -> Int32

Parameters

  • generator:

    The random number generator.

  • state_size:

    The size of the state buffer, in bytes.

  • state:

    A pointer to the state.

Discussion

Use the BNNSRandomGeneratorGetState(_:_:_:) and BNNSRandomGeneratorSetState(_:_:_:) functions to capture and restore a random number generator’s state.

The following code creates a random number generator and captures its initial state. The code calls BNNSRandomFillUniformInt(_:_:_:_:) twice and copies the random values into the arrays a and b. The BNNSRandomGeneratorSetState(_:_:_:) function restores the generator to its initial state, and the final call to BNNSRandomFillUniformInt(_:_:_:_:) populates the descriptor so that the values in arrays a and c are equal.

let data = UnsafeMutableBufferPointer<Int16>.allocate(capacity: 8)
var descriptor = BNNSNDArrayDescriptor(flags: BNNSNDArrayFlags(0),
                                       layout: BNNSDataLayoutVector,
                                       size: (10, 0, 0, 0, 0, 0, 0, 0),
                                       stride: (0, 0, 0, 0, 0, 0, 0, 0),
                                       data: data.baseAddress!,
                                       data_type: BNNSDataType.int16,
                                       table_data: nil,
                                       table_data_type: BNNSDataType.int16,
                                       data_scale: 1, data_bias: 0)

guard let randomNumberGenerator = BNNSCreateRandomGenerator(BNNSRandomGeneratorMethodAES_CTR,
                                                            nil) else {
    return
}

// Allocate memory to store state.
let stateSize = BNNSRandomGeneratorStateSize(randomNumberGenerator)
let state = UnsafeMutableRawPointer.allocate(byteCount: stateSize,
                                             alignment: 0)

// Store the random number generator's state.
BNNSRandomGeneratorGetState(randomNumberGenerator,
                            stateSize,
                            state)

BNNSRandomFillUniformInt(randomNumberGenerator,
                         &descriptor,
                         -10,
                         10)

let a = Array(data)

BNNSRandomFillUniformInt(randomNumberGenerator,
                         &descriptor,
                         -10,
                         10)

let b = Array(data)

// Set the random number generator's state to its initial state.
BNNSRandomGeneratorSetState(randomNumberGenerator,
                            stateSize,
                            state)

BNNSRandomFillUniformInt(randomNumberGenerator,
                         &descriptor,
                         -10,
                         10)

let c = Array(data)

print(a.elementsEqual(c)) // prints "true"

data.deallocate()
state.deallocate()
BNNSDestroyRandomGenerator(randomNumberGenerator)

See Also

Random number generation