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import SwiftShims // For swift_stdlib_random
/// A type that provides random bytes.
///
/// This type is similar to `RandomNumberGenerator` in Swift standard library,
/// but it provides a way to fill a buffer with random bytes instead of a single
/// random number.
public protocol RandomBufferGenerator {
/// Fills the buffer with random bytes.
///
/// - Parameter buffer: The destination buffer to fill with random bytes.
mutating func fill(buffer: UnsafeMutableBufferPointer<UInt8>)
}
extension RandomBufferGenerator where Self: RandomNumberGenerator {
public mutating func fill(buffer: UnsafeMutableBufferPointer<UInt8>) {
// The buffer is filled with 8 bytes at once.
let count = buffer.count / 8
for i in 0..<count {
let random = self.next()
withUnsafeBytes(of: random) { randomBytes in
let startOffset = i * 8
let destination = UnsafeMutableBufferPointer(rebasing: buffer[startOffset..<(startOffset + 8)])
UnsafeMutableRawBufferPointer(destination).copyMemory(from: randomBytes)
}
}
// If the buffer size is not a multiple of 8, fill the remaining bytes.
let remaining = buffer.count % 8
if remaining > 0 {
let random = self.next()
withUnsafeBytes(of: random) { randomBytes in
let startOffset = count * 8
let destination = UnsafeMutableBufferPointer(rebasing: buffer[startOffset..<(startOffset + remaining)])
UnsafeMutableRawBufferPointer(destination).copyMemory(
from: UnsafeRawBufferPointer(start: randomBytes.baseAddress, count: remaining)
)
}
}
}
}
extension SystemRandomNumberGenerator: RandomBufferGenerator {
public mutating func fill(buffer: UnsafeMutableBufferPointer<UInt8>) {
guard let baseAddress = buffer.baseAddress else { return }
// Directly call underlying C function of SystemRandomNumberGenerator
swift_stdlib_random(baseAddress, Int(buffer.count))
}
}
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