Add _stdlib_random for more platforms (#1)

* Remove refs to Countable ranges

* Add `_stdlib_random` for more platforms

* Use `getrandom` (if available) for Android, Cygwin

* Reorder the `_stdlib_random` functions

* Also include <features.h> on Linux

* Add `#error TODO` in `_stdlib_random` for Windows

* Colon after Fatal Error

Performance improvement for Random

gybify ranges

Fix typo in 'basic random numbers'
Add _stdlib_random as a testable method

Switch to generic constraints

Hopefully link against bcrypt

Fix some implementation details

1. Uniform distribution is now uniform
2. Apply Jens' method for uniform floats

Fix a lineable attribute

stdlib/public/core/Bool.swift

@@ -92,12 +92,24 @@ public struct Bool {
   /// - Parameter generator: The random number generator to use when getting a
   ///   random Boolean.
   /// - Returns: A random Boolean.
-  @_inlineable
-  public static func random(
-    using generator: RandomNumberGenerator = Random.default
+  @inlinable
+  public static func random<T: RandomNumberGenerator>(
+    using generator: T
   ) -> Bool {
     return generator.next() % 2 == 0
   }
+  
+  /// Returns a random Boolean
+  ///
+  /// - Parameter generator: The random number generator to use when getting a
+  ///   random Boolean.
+  /// - Returns: A random Boolean.
+  ///
+  /// This uses the standard library's default random number generator.
+  @inlinable
+  public static func random() -> Bool {
+    return Bool.random(using: Random.default)
+  }
 }
 
 extension Bool : _ExpressibleByBuiltinBooleanLiteral, ExpressibleByBooleanLiteral {

stdlib/public/core/CMakeLists.txt

@@ -229,6 +229,10 @@ if(CMAKE_SYSTEM_NAME STREQUAL "FreeBSD")
       ${EXECINFO_LIBRARY})
 endif()
 
+if(CMAKE_SYSTEM_NAME STREQUAL "Windows")
+  list(APPEND swift_core_link_flags "$ENV{SystemRoot}/system32/bcrypt.dll")
+endif()
+
 option(SWIFT_CHECK_ESSENTIAL_STDLIB
     "Check core standard library layering by linking its essential subset"
     FALSE)

stdlib/public/core/ClosedRange.swift

@@ -480,57 +480,6 @@ extension ClosedRange where Bound: Strideable, Bound.Stride : SignedInteger {
   }
 }
 
-extension ClosedRange
-where Bound : FixedWidthInteger,
-      Bound.Magnitude : UnsignedInteger {
-
-  /// Returns a random element from this collection.
-  ///
-  /// - Parameter generator: The random number generator to use when getting
-  ///   a random element.
-  /// - Returns: A random element from this collection.
-  ///
-  /// A good example of this is getting a random greeting from an array:
-  ///
-  ///     let greetings = ["hi", "hey", "hello", "hola"]
-  ///     let randomGreeting = greetings.random()
-  ///
-  /// If the collection is empty, the value of this function is `nil`.
-  ///
-  ///     let numbers = [10, 20, 30, 40, 50]
-  ///     if let randomNumber = numbers.random() {
-  ///         print(randomNumber)
-  ///     }
-  ///     // Could print "20", perhaps
-  @_inlineable
-  public func random(
-    using generator: RandomNumberGenerator = Random.default
-  ) -> Element? {
-    let isLowerNegative = Bound.isSigned && lowerBound < 0
-    let sameSign = !Bound.isSigned || isLowerNegative == (upperBound < 0)
-    var delta: Bound.Magnitude
-    if isLowerNegative {
-      delta = sameSign
-        ? lowerBound.magnitude - upperBound.magnitude
-        : lowerBound.magnitude + upperBound.magnitude
-    } else {
-      delta = upperBound.magnitude - lowerBound.magnitude
-    }
-    if delta == Bound.Magnitude.max {
-      return Bound(truncatingIfNeeded: generator.next() as Bound.Magnitude)
-    }
-    delta += 1
-    let randomMagnitude = generator.next(upperBound: delta)
-    if sameSign {
-      return lowerBound + Bound(randomMagnitude)
-    } else {
-      return Bound.isSigned && randomMagnitude <= upperBound.magnitude
-        ? Bound(randomMagnitude)
-        : 0 - Bound(randomMagnitude - upperBound.magnitude)
-    }
-  }
-}
-
 extension ClosedRange {
   @inlinable
   public func overlaps(_ other: ClosedRange<Bound>) -> Bool {

stdlib/public/core/Collection.swift

@@ -1034,12 +1034,12 @@ extension Collection {
   ///         print(randomNumber)
   ///     }
   ///     // Could print "20", perhaps
-  @_inlineable
-  public func random(
-    using generator: RandomNumberGenerator = Random.default
+  @inlinable
+  public func random<T: RandomNumberGenerator>(
+    using generator: T
   ) -> Element? {
     guard !isEmpty else { return nil }
-    let random = generator.next(upperBound: UInt(self.count))
+    let random = generator.next(upperBound: UInt(count))
     let index = self.index(
       self.startIndex,
       offsetBy: IndexDistance(random),
@@ -1048,6 +1048,31 @@ extension Collection {
     return self[index]
   }
 
+  /// Returns a random element from this collection.
+  ///
+  /// - Parameter generator: The random number generator to use when getting
+  ///   a random element.
+  /// - Returns: A random element from this collection.
+  ///
+  /// A good example of this is getting a random greeting from an array:
+  ///
+  ///     let greetings = ["hi", "hey", "hello", "hola"]
+  ///     let randomGreeting = greetings.random()
+  ///
+  /// If the collection is empty, the value of this function is `nil`.
+  ///
+  ///     let numbers = [10, 20, 30, 40, 50]
+  ///     if let randomNumber = numbers.random() {
+  ///         print(randomNumber)
+  ///     }
+  ///     // Could print "20", perhaps
+  ///
+  /// This uses the standard library's default random number generator.
+  @inlinable
+  public func random() -> Element? {
+    return random(using: Random.default)
+  }
+
   /// Do not use this method directly; call advanced(by: n) instead.
   @inlinable
   @inline(__always)

stdlib/public/core/CollectionAlgorithms.swift

@@ -368,7 +368,7 @@ extension MutableCollection where Self : BidirectionalCollection {
 }
 
 //===----------------------------------------------------------------------===//
-// shuffled()
+// shuffled()/shuffle()
 //===----------------------------------------------------------------------===//
 
 extension Sequence {
@@ -377,14 +377,26 @@ extension Sequence {
   /// - Parameter generator: The random number generator to use when shuffling
   ///   the sequence.
   /// - Returns: A shuffled array of this sequence's elements.
-  @_inlineable
-  public func shuffled(
-    using generator: RandomNumberGenerator = Random.default
+  @inlinable
+  public func shuffled<T: RandomNumberGenerator>(
+    using generator: T
   ) -> [Element] {
     var result = ContiguousArray(self)
     result.shuffle(using: generator)
     return Array(result)
   }
+  
+  /// Returns the elements of the sequence, shuffled.
+  ///
+  /// - Parameter generator: The random number generator to use when shuffling
+  ///   the sequence.
+  /// - Returns: A shuffled array of this sequence's elements.
+  ///
+  /// This uses the standard library's default random number generator.
+  @inlinable
+  public func shuffled() -> [Element] {
+    return shuffled(using: Random.default)
+  }
 }
 
 extension MutableCollection {
@@ -392,9 +404,9 @@ extension MutableCollection {
   ///
   /// - Parameter generator: The random number generator to use when shuffling
   ///   the collection.
-  @_inlineable
-  public mutating func shuffle(
-    using generator: RandomNumberGenerator = Random.default
+  @inlinable
+  public mutating func shuffle<T: RandomNumberGenerator>(
+    using generator: T
   ) {
     guard count > 1 else { return }
     var amount = count
@@ -409,6 +421,17 @@ extension MutableCollection {
       formIndex(after: &currentIndex)
     }
   }
+  
+  /// Shuffles the collection in place.
+  ///
+  /// - Parameter generator: The random number generator to use when shuffling
+  ///   the collection.
+  ///
+  /// This uses the standard library's default random number generator.
+  @inlinable
+  public mutating func shuffle() {
+    shuffle(using: Random.default)
+  }
 }
 
 //===----------------------------------------------------------------------===//

stdlib/public/core/FloatingPoint.swift.gyb

@@ -2413,10 +2413,10 @@ where Self.RawSignificand : FixedWidthInteger,
   /// - Parameter generator: The random number generator to use when getting
   ///   the random floating point.
   /// - Returns: A random representation of this floating point.
-  @_inlineable
-  public static func random(
+  @inlinable
+  public static func random<T: RandomNumberGenerator>(
     in range: ${Range}<Self>,
-    using generator: RandomNumberGenerator = Random.default
+    using generator: T
   ) -> Self {
 %   if 'Closed' not in Range:
     _precondition(
@@ -2425,7 +2425,7 @@ where Self.RawSignificand : FixedWidthInteger,
     )
 %   end
     let delta = range.upperBound - range.lowerBound
-    let maxSignificand: Self.RawSignificand = 1 << Self.significandBitCount
+    let maxSignificand = Self.RawSignificand(1 << (Self.significandBitCount + 1))
 %   if 'Closed' not in Range:
     let rand: Self.RawSignificand = generator.next(upperBound: maxSignificand)
 %   else:
@@ -2434,14 +2434,23 @@ where Self.RawSignificand : FixedWidthInteger,
       return range.upperBound
     }
 %   end
-    let unitRandom = Self.init(
-      sign: .plus,
-      exponentBitPattern: (1 as Self).exponentBitPattern,
-      significandBitPattern: rand
-    ) - 1
+    let unitRandom = Self.init(rand) * Self.ulpOfOne / 2
     return delta * unitRandom + range.lowerBound
   }
 
+  /// Returns a random representation of this floating point within the range.
+  ///
+  /// - Parameter range: A ${Range} to determine the bounds to get a random value
+  ///   from.
+  /// - Parameter generator: The random number generator to use when getting
+  ///   the random floating point.
+  /// - Returns: A random representation of this floating point.
+  ///
+  /// This uses the standard library's default random number generator.
+  @inlinable
+  public static func random(in range: ${Range}<Self>) -> Self {
+    return Self.random(in: range, using: Random.default)
+  }
 }
 
 % end

stdlib/public/core/Integers.swift.gyb

@@ -2532,6 +2532,99 @@ ${assignmentOperatorComment(x.operator, False)}
 
 % for Range in ['Range', 'ClosedRange']:
 
+extension ${Range}
+where Bound: FixedWidthInteger,
+      Bound.Magnitude: UnsignedInteger {
+      
+  /// Returns a random element from this collection.
+  ///
+  /// - Parameter generator: The random number generator to use when getting
+  ///   a random element.
+  /// - Returns: A random element from this collection.
+  ///
+  /// A good example of this is getting a random greeting from an array:
+  ///
+  ///     let greetings = ["hi", "hey", "hello", "hola"]
+  ///     let randomGreeting = greetings.random()
+  ///
+  /// If the collection is empty, the value of this function is `nil`.
+  ///
+  ///     let numbers = [10, 20, 30, 40, 50]
+  ///     if let randomNumber = numbers.random() {
+  ///         print(randomNumber)
+  ///     }
+  ///     // Could print "20", perhaps
+  @inlinable
+  public func random<T: RandomNumberGenerator>(
+    using generator: T
+  ) -> Element? {
+%   if 'Closed' not in Range:
+    guard lowerBound != upperBound else {
+      return nil
+    }
+%   end
+    let isLowerNegative = Bound.isSigned && lowerBound < 0
+    let sameSign = !Bound.isSigned || isLowerNegative == (upperBound < 0)
+%   if 'Closed' not in Range:
+    let delta: Bound.Magnitude
+%   else:
+    var delta: Bound.Magnitude
+%   end
+    if isLowerNegative {
+      delta = sameSign
+        ? lowerBound.magnitude - upperBound.magnitude
+        : lowerBound.magnitude + upperBound.magnitude
+    } else {
+      delta = upperBound.magnitude - lowerBound.magnitude
+    }
+%   if 'Closed' in Range:
+    if delta == Bound.Magnitude.max {
+      return Bound(truncatingIfNeeded: generator.next() as Bound.Magnitude)
+    }
+    delta += 1
+%   end
+    let randomMagnitude = generator.next(upperBound: delta)
+    if sameSign {
+      return lowerBound + Bound(randomMagnitude)
+    } else {
+%     if 'Closed' not in Range:
+      return randomMagnitude < upperBound.magnitude
+        ? Bound(randomMagnitude)
+        : -1 - Bound(randomMagnitude - upperBound.magnitude)
+%     else:
+      return Bound.isSigned && randomMagnitude <= upperBound.magnitude
+        ? Bound(randomMagnitude)
+        : 0 - Bound(randomMagnitude - upperBound.magnitude)
+%     end
+    }
+  }
+  
+  /// Returns a random element from this collection.
+  ///
+  /// - Parameter generator: The random number generator to use when getting
+  ///   a random element.
+  /// - Returns: A random element from this collection.
+  ///
+  /// A good example of this is getting a random greeting from an array:
+  ///
+  ///     let greetings = ["hi", "hey", "hello", "hola"]
+  ///     let randomGreeting = greetings.random()
+  ///
+  /// If the collection is empty, the value of this function is `nil`.
+  ///
+  ///     let numbers = [10, 20, 30, 40, 50]
+  ///     if let randomNumber = numbers.random() {
+  ///         print(randomNumber)
+  ///     }
+  ///     // Could print "20", perhaps
+  ///
+  /// This uses the standard library's default random number generator.
+  @inlinable
+  public func random() -> Element? {
+    return self.random(using: Random.default)
+  }
+}
+
 extension FixedWidthInteger
 where Self.Stride : SignedInteger,
       Self.Magnitude : UnsignedInteger {
@@ -2543,10 +2636,10 @@ where Self.Stride : SignedInteger,
   /// - Parameter generator: The random number generator to use when getting
   ///   the random integer.
   /// - Returns: A random representation of this integer.
-  @_inlineable
-  public static func random(
+  @inlinable
+  public static func random<T: RandomNumberGenerator>(
     in range: ${Range}<Self>,
-    using generator: RandomNumberGenerator = Random.default
+    using generator: T
   ) -> Self {
 %   if 'Closed' not in Range:
     _precondition(
@@ -2556,6 +2649,20 @@ where Self.Stride : SignedInteger,
 %   end
     return range.random(using: generator)!
   }
+  
+  /// Returns a random representation of this integer within the range.
+  ///
+  /// - Parameter range: A ${Range} to determine the bounds to get a random value
+  ///   from.
+  /// - Parameter generator: The random number generator to use when getting
+  ///   the random integer.
+  /// - Returns: A random representation of this integer.
+  ///
+  /// This uses the standard library's default random number generator.
+  @inlinable
+  public static func random(in range: ${Range}<Self>) -> Self {
+    return Self.random(in: range, using: Random.default)
+  }
 }
 
 % end

stdlib/public/core/Random.swift

@@ -46,10 +46,10 @@ extension RandomNumberGenerator {
   ///
   /// This differs from next() as this function has the ability to transform the
   /// generated number to any unsigned integer.
-  @_inlineable
+  @inlinable
   public func next<T: FixedWidthInteger & UnsignedInteger>() -> T {
-    if T.bitWidth == UInt64.bitWidth {
-      return T(self.next())
+    if T.bitWidth <= UInt64.bitWidth {
+      return T(truncatingIfNeeded: self.next())
     }
 
     let (quotient, remainder) = T.bitWidth.quotientAndRemainder(
@@ -76,11 +76,12 @@ extension RandomNumberGenerator {
   /// - Parameter upperBound: The max number this can generate up to.
   /// - Returns: A number that was randomly generated from 0 to upperBound
   ///
-  /// This uses the uniform distribution to form a random number within the
-  /// upperBound.
-  @_inlineable
+  /// By default, this uses the uniform distribution to form a random number
+  /// that is less than the upperBound.
+  @inlinable
   public func next<T: FixedWidthInteger & UnsignedInteger>(upperBound: T) -> T {
-    let range = T.max % upperBound
+    let tmp = (T.max % upperBound) + 1
+    let range = tmp == upperBound ? 0 : tmp
     var random: T = 0
 
     repeat {
@@ -125,4 +126,23 @@ public struct Random : RandomNumberGenerator {
     _stdlib_random(&random, MemoryLayout<UInt64>.size)
     return random
   }
+  
+  /// Produces the next randomly generated number
+  ///
+  /// - Returns: A number that was randomly generated
+  ///
+  /// This differs from next() as this function has the ability to transform the
+  /// generated number to any unsigned integer.
+  public func next<T: FixedWidthInteger & UnsignedInteger>() -> T {
+    var random: T = 0
+    _stdlib_random(&random, MemoryLayout<T>.size)
+    return random
+  }
+}
+
+public // @testable
+func _stdlib_random(_ bytes: UnsafeMutableRawBufferPointer) {
+  if !bytes.isEmpty {
+    _stdlib_random(bytes.baseAddress!, bytes.count)
+  }
 }

stdlib/public/core/Range.swift

@@ -303,56 +303,6 @@ extension Range where Bound: Strideable, Bound.Stride : SignedInteger {
   }
 }
 
-extension Range
-where Bound : FixedWidthInteger,
-      Bound.Magnitude : UnsignedInteger {
-
-  /// Returns a random element from this collection.
-  ///
-  /// - Parameter generator: The random number generator to use when getting
-  ///   a random element.
-  /// - Returns: A random element from this collection.
-  ///
-  /// A good example of this is getting a random greeting from an array:
-  ///
-  ///     let greetings = ["hi", "hey", "hello", "hola"]
-  ///     let randomGreeting = greetings.random()
-  ///
-  /// If the collection is empty, the value of this function is `nil`.
-  ///
-  ///     let numbers = [10, 20, 30, 40, 50]
-  ///     if let randomNumber = numbers.random() {
-  ///         print(randomNumber)
-  ///     }
-  ///     // Could print "20", perhaps
-  @_inlineable
-  public func random(
-    using generator: RandomNumberGenerator = Random.default
-  ) -> Element? {
-    guard lowerBound != upperBound else {
-      return nil
-    }
-    let isLowerNegative = Bound.isSigned && lowerBound < 0
-    let sameSign = !Bound.isSigned || isLowerNegative == (upperBound < 0)
-    let delta: Bound.Magnitude
-    if isLowerNegative {
-      delta = sameSign
-        ? lowerBound.magnitude - upperBound.magnitude
-        : lowerBound.magnitude + upperBound.magnitude
-    } else {
-      delta = upperBound.magnitude - lowerBound.magnitude
-    }
-    let randomMagnitude = generator.next(upperBound: delta)
-    if sameSign {
-      return lowerBound + Bound(randomMagnitude)
-    } else {
-      return randomMagnitude < upperBound.magnitude
-        ? Bound(randomMagnitude)
-        : -1 - Bound(randomMagnitude - upperBound.magnitude)
-    }
-  }
-}
-
 extension Range: RangeExpression {
   /// Returns the range of indices described by this range expression within
   /// the given collection.

stdlib/public/stubs/LibcShims.cpp

@@ -11,35 +11,67 @@
 //===----------------------------------------------------------------------===//
 
 #if defined(__APPLE__)
-#define _REENTRANT
-#include <math.h>
-#endif
-#include <random>
-#include <type_traits>
-#include <cmath>
-#if defined(_WIN32)
-#include <io.h>
-#define WIN32_LEAN_AND_MEAN
-#include <Windows.h>
-#else
-#include <unistd.h>
-#include <pthread.h>
-#include <semaphore.h>
-#include <sys/ioctl.h>
+#  define _REENTRANT
+#  include <math.h>
+#  include <Security/Security.h>
 #endif
 
-#include <stdlib.h>
-#include <stdio.h>
-#include <string.h>
-#include <fcntl.h>
+#if defined(__CYGWIN__)
+#  include <cygwin/version.h>
+#  if (CYGWIN_VERSION_API_MAJOR > 0) || (CYGWIN_VERSION_API_MINOR >= 306)
+#    include <sys/random.h>
+#    define SWIFT_STDLIB_USING_GETRANDOM
+#  endif
+#endif
+
+#if defined(__Fuchsia__)
+#  include <sys/random.h>
+#  define SWIFT_STDLIB_USING_GETENTROPY
+#endif
+
+#if defined(__linux__)
+#  include <linux/version.h>
+#  if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0))
+#    include <features.h>
+#    if defined(__BIONIC__) || (defined(__GLIBC_PREREQ) && __GLIBC_PREREQ(2,25))
+#      include <sys/random.h>
+#      define SWIFT_STDLIB_USING_GETRANDOM
+#    endif
+#  endif
+#endif
+
+#if defined(_WIN32) && !defined(__CYGWIN__)
+#  include <io.h>
+#  define WIN32_LEAN_AND_MEAN
+#  define WIN32_NO_STATUS
+#    include <Windows.h>
+#  undef WIN32_NO_STATUS
+#  include <Ntstatus.h>
+#  include <Ntdef.h>
+#  include <Bcrypt.h>
+#else
+#  include <pthread.h>
+#  include <semaphore.h>
+#  include <sys/ioctl.h>
+#  include <unistd.h>
+#endif
+
+#include <cmath>
 #include <errno.h>
-#include <sys/types.h>
+#include <fcntl.h>
+#include <random>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
 #include <sys/stat.h>
+#include <sys/types.h>
+#include <type_traits>
+
+#include "llvm/Support/DataTypes.h"
 #include "swift/Basic/Lazy.h"
 #include "swift/Runtime/Config.h"
 #include "swift/Runtime/Debug.h"
 #include "../SwiftShims/LibcShims.h"
-#include "llvm/Support/DataTypes.h"
 
 using namespace swift;
 
@@ -311,44 +343,72 @@ swift::_stdlib_cxx11_mt19937_uniform(__swift_uint32_t upper_bound) {
 }
 
 #if defined(__APPLE__)
-#include <Security/Security.h>
+
 SWIFT_RUNTIME_STDLIB_INTERNAL
 void swift::_stdlib_random(void *buf, __swift_size_t nbytes) {
   if (__builtin_available(macOS 10.12, iOS 10, tvOS 10, watchOS 3, *)) {
     arc4random_buf(buf, nbytes);
-  }else {
+  } else {
     OSStatus status = SecRandomCopyBytes(kSecRandomDefault, nbytes, buf);
     if (status != errSecSuccess) {
-      fatalError(0, "Fatal error: SecRandomCopyBytes failed with error %d\n", status);
+      fatalError(0, "Fatal error: %d in '%s'\n", status, __func__);
     }
   }
 }
-#elif defined(__linux__)
-#include <linux/version.h>
-#include <sys/syscall.h>
+
+#elif defined(_WIN32) && !defined(__CYGWIN__)
+// TODO: Test on Windows
+
 SWIFT_RUNTIME_STDLIB_INTERNAL
 void swift::_stdlib_random(void *buf, __swift_size_t nbytes) {
-#if LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)
-  auto _read = [&]() -> __swift_ssize_t {
-    return syscall(SYS_getrandom, buf, bytes, 0);
-  };
-#else
-  auto _read = [&]() -> __swift_ssize_t {
-    static const int fd = _stdlib_open("/dev/urandom", O_RDONLY);
-    if (fd < 0) {
-      fatalError(0, "Unable to open '/dev/urandom'\n");
-    }
-    return _stdlib_read(fd, buf, bytes);
-  };
-#endif
-  while (nbytes > 0) {
-    auto result = _read();
-    if (result < 1) {
-      if (errno == EINTR) { continue; }
-      fatalError(0, "Unable to read '/dev/urandom'\n");
-    }
-    buf = static_cast<uint8_t *>(buf) + result;
-    nbytes -= result;
+  NTSTATUS status = BCryptGenRandom(nullptr,
+                                    static_cast<PUCHAR>(buf),
+                                    static_cast<ULONG>(nbytes),
+                                    BCRYPT_USE_SYSTEM_PREFERRED_RNG);
+  if (!NT_SUCCESS(status)) {
+    fatalError(0, "Fatal error: %#.8x in '%s'\n", status, __func__);
   }
 }
+
+#elif defined(SWIFT_STDLIB_USING_GETENTROPY)
+
+SWIFT_RUNTIME_STDLIB_INTERNAL
+void swift::_stdlib_random(void *buf, __swift_size_t nbytes) {
+  while (nbytes > 0) {
+    constexpr __swift_size_t max_nbytes = 256;
+    __swift_size_t actual_nbytes = (nbytes < max_nbytes ?
+                                    nbytes : max_nbytes);
+    if (0 != getentropy(buf, actual_nbytes)) {
+      fatalError(0, "Fatal error: %d in '%s'\n", errno, __func__);
+    }
+    buf = static_cast<uint8_t *>(buf) + actual_nbytes;
+    nbytes -= actual_nbytes;
+  }
+}
+
+#else
+
+SWIFT_RUNTIME_STDLIB_INTERNAL
+void swift::_stdlib_random(void *buf, __swift_size_t nbytes) {
+#if !defined(SWIFT_STDLIB_USING_GETRANDOM)
+  static const int fd = _stdlib_open("/dev/urandom", O_RDONLY, 0);
+  if (fd < 0) {
+    fatalError(0, "Fatal error: %d in '%s'\n", errno, __func__);
+  }
+#endif
+  while (nbytes > 0) {
+#if !defined(SWIFT_STDLIB_USING_GETRANDOM)
+    __swift_ssize_t actual_nbytes = _stdlib_read(fd, buf, nbytes);
+#else
+    __swift_ssize_t actual_nbytes = getrandom(buf, nbytes, 0);
+#endif
+    if (actual_nbytes < 1) {
+      if (errno == EINTR) { continue; }
+      fatalError(0, "Fatal error: %d in '%s'\n", errno, __func__);
+    }
+    buf = static_cast<uint8_t *>(buf) + actual_nbytes;
+    nbytes -= actual_nbytes;
+  }
+}
+
 #endif

test/stdlib/Random.swift

@@ -15,7 +15,7 @@ RandomTests.test("basic random numbers") {
   let randomDouble1 = Double.random(in: 0 ..< 1)
   expectTrue(randomDouble1 < 1 && randomDouble1 >= 0)
   let randomDouble2 = Double.random(in: 0 ..< 1)
-  expectTrue(randomDouble1 < 1 && randomDouble2 >= 0)
+  expectTrue(randomDouble2 < 1 && randomDouble2 >= 0)
   expectTrue(randomDouble1 != randomDouble2)
 }