many improvements to random.nim; fixes #4726

changelog.md

@@ -128,3 +128,7 @@ This now needs to be written as:
   strings and chars.
 - Removed ``securehash`` stdlib module as it is not secure anymore. The module
   is still available via ``compiler/securehash``.
+- The ``random`` procs in ``random.nim`` have all been deprecated. Instead use
+  the new ``rand`` procs. The module now exports the state of the random
+  number generator as type ``Rand`` so multiple threads can easily use their
+  own random number generators that do not require locking.

lib/pure/random.nim

@@ -7,16 +7,16 @@
 #    distribution, for details about the copyright.
 #
 
-## Nim's standard random number generator. Based on the ``xoroshiro128+`` (xor/rotate/shift/rotate) library.
+## Nim's standard random number generator. Based on
+## the ``xoroshiro128+`` (xor/rotate/shift/rotate) library.
 ## * More information: http://xoroshiro.di.unimi.it/
 ## * C implementation: http://xoroshiro.di.unimi.it/xoroshiro128plus.c
 ##
-## Do not use this module for cryptographic use!
+## **Do not use this module for cryptographic purposes!**
 
 include "system/inclrtl"
 {.push debugger:off.}
 
-# XXX Expose RandomGenState
 when defined(JS):
   type ui = uint32
 
@@ -27,31 +27,34 @@ else:
   const randMax = 18_446_744_073_709_551_615u64
 
 type
-  RandomGenState = object
+  Rand* = object ## State of the random number generator.
+                 ## The procs that use the default state
+                 ## are **not** thread-safe!
     a0, a1: ui
 
 when defined(JS):
-  var state = RandomGenState(
+  var state = Rand(
     a0: 0x69B4C98Cu32,
     a1: 0xFED1DD30u32) # global for backwards compatibility
 else:
   # racy for multi-threading but good enough for now:
-  var state = RandomGenState(
+  var state = Rand(
     a0: 0x69B4C98CB8530805u64,
     a1: 0xFED1DD3004688D67CAu64) # global for backwards compatibility
 
 proc rotl(x, k: ui): ui =
   result = (x shl k) or (x shr (ui(64) - k))
 
-proc next(s: var RandomGenState): uint64 =
+proc next*(r: var Rand): uint64 =
-  let s0 = s.a0
+  ## Uses the state to compute a new ``uint64`` random number.
-  var s1 = s.a1
+  let s0 = r.a0
+  var s1 = r.a1
   result = s0 + s1
   s1 = s1 xor s0
-  s.a0 = rotl(s0, 55) xor s1 xor (s1 shl 14) # a, b
+  r.a0 = rotl(s0, 55) xor s1 xor (s1 shl 14) # a, b
-  s.a1 = rotl(s1, 36) # c
+  r.a1 = rotl(s1, 36) # c
 
-proc skipRandomNumbers(s: var RandomGenState) =
+proc skipRandomNumbers*(s: var Rand) =
   ## This is the jump function for the generator. It is equivalent
   ## to 2^64 calls to next(); it can be used to generate 2^64
   ## non-overlapping subsequences for parallel computations.
@@ -71,21 +74,23 @@ proc skipRandomNumbers(s: var RandomGenState) =
   s.a0 = s0
   s.a1 = s1
 
-proc random*(max: int): int {.benign.} =
+proc random*(max: int): int {.benign, deprecated.} =
   ## Returns a random number in the range 0..max-1. The sequence of
   ## random number is always the same, unless `randomize` is called
   ## which initializes the random number generator with a "random"
-  ## number, i.e. a tickcount.
+  ## number, i.e. a tickcount. **Deprecated since version 0.18.0**.
+  ## Use ``rand`` instead.
   while true:
     let x = next(state)
     if x < randMax - (randMax mod ui(max)):
       return int(x mod uint64(max))
 
-proc random*(max: float): float {.benign.} =
+proc random*(max: float): float {.benign, deprecated.} =
   ## Returns a random number in the range 0..<max. The sequence of
   ## random number is always the same, unless `randomize` is called
   ## which initializes the random number generator with a "random"
-  ## number, i.e. a tickcount.
+  ## number, i.e. a tickcount. **Deprecated since version 0.18.0**.
+  ## Use ``rand`` instead.
   let x = next(state)
   when defined(JS):
     result = (float(x) / float(high(uint32))) * max
@@ -93,25 +98,91 @@ proc random*(max: float): float {.benign.} =
     let u = (0x3FFu64 shl 52u64) or (x shr 12u64)
     result = (cast[float](u) - 1.0) * max
 
-proc random*[T](x: HSlice[T, T]): T =
+proc random*[T](x: HSlice[T, T]): T {.deprecated.} =
   ## For a slice `a .. b` returns a value in the range `a .. b-1`.
+  ## **Deprecated since version 0.18.0**.
+  ## Use ``rand`` instead.
   result = T(random(x.b - x.a)) + x.a
 
-proc random*[T](a: openArray[T]): T =
+proc random*[T](a: openArray[T]): T {.deprecated.} =
   ## returns a random element from the openarray `a`.
+  ## **Deprecated since version 0.18.0**.
+  ## Use ``rand`` instead.
   result = a[random(a.low..a.len)]
 
+proc rand*(r: var Rand; max: int): int {.benign.} =
+  ## Returns a random number in the range 0..max. The sequence of
+  ## random number is always the same, unless `randomize` is called
+  ## which initializes the random number generator with a "random"
+  ## number, i.e. a tickcount.
+  while true:
+    let x = next(r)
+    if x <= randMax - (randMax mod ui(max)):
+      return int(x mod (uint64(max)+1u64))
+
+proc rand*(max: int): int {.benign.} =
+  ## Returns a random number in the range 0..max. The sequence of
+  ## random number is always the same, unless `randomize` is called
+  ## which initializes the random number generator with a "random"
+  ## number, i.e. a tickcount.
+  rand(state, max)
+
+proc rand*(r: var Rand; max: float): float {.benign.} =
+  ## Returns a random number in the range 0..max. The sequence of
+  ## random number is always the same, unless `randomize` is called
+  ## which initializes the random number generator with a "random"
+  ## number, i.e. a tickcount.
+  let x = next(r)
+  when defined(JS):
+    result = (float(x) / float(high(uint32))) * max
+  else:
+    let u = (0x3FFu64 shl 52u64) or (x shr 12u64)
+    result = (cast[float](u) - 1.0) * max
+
+proc rand*(max: float): float {.benign.} =
+  ## Returns a random number in the range 0..max. The sequence of
+  ## random number is always the same, unless `randomize` is called
+  ## which initializes the random number generator with a "random"
+  ## number, i.e. a tickcount.
+  rand(state, max)
+
+proc rand*[T](r: var Rand; x: HSlice[T, T]): T =
+  ## For a slice `a .. b` returns a value in the range `a .. b`.
+  result = T(rand(r, x.b - x.a)) + x.a
+
+proc rand*[T](x: HSlice[T, T]): T =
+  ## For a slice `a .. b` returns a value in the range `a .. b`.
+  result = rand(state, x)
+
+proc rand*[T](r: var Rand; a: openArray[T]): T =
+  ## returns a random element from the openarray `a`.
+  result = a[rand(r, a.low..a.high)]
+
+proc rand*[T](a: openArray[T]): T =
+  ## returns a random element from the openarray `a`.
+  result = a[rand(a.low..a.high)]
+
+
+proc initRand*(seed: int64): Rand =
+  ## Creates a new ``Rand`` state from ``seed``.
+  result.a0 = ui(seed shr 16)
+  result.a1 = ui(seed and 0xffff)
+  discard next(result)
+
 proc randomize*(seed: int64) {.benign.} =
-  ## Initializes the random number generator with a specific seed.
+  ## Initializes the default random number generator
-  state.a0 = ui(seed shr 16)
+  ## with a specific seed.
-  state.a1 = ui(seed and 0xffff)
+  state = initRand(seed)
-  discard next(state)
+
+proc shuffle*[T](r: var Rand; x: var openArray[T]) =
+  ## Swaps the positions of elements in a sequence randomly.
+  for i in countdown(x.high, 1):
+    let j = r.rand(i)
+    swap(x[i], x[j])
 
 proc shuffle*[T](x: var openArray[T]) =
-  ## Will randomly swap the positions of elements in a sequence.
+  ## Swaps the positions of elements in a sequence randomly.
-  for i in countdown(x.high, 1):
+  shuffle(state, x)
-    let j = random(i + 1)
-    swap(x[i], x[j])
 
 when not defined(nimscript):
   import times
@@ -134,7 +205,7 @@ when isMainModule:
 
     var x = 8234
     for i in 0..100_000:
-      x = random(len(occur)) # myrand(x)
+      x = rand(high(occur))
       inc occur[x]
     for i, oc in occur:
       if oc < 69: