1 files changed, 45 insertions, 5 deletions
diff --git a/lib/pure/random.nim b/lib/pure/random.nim
index c458d51eb..378ca6f87 100644
--- a/lib/pure/random.nim
+++ b/lib/pure/random.nim
@@ -14,6 +14,8 @@
 ##
 ## **Do not use this module for cryptographic purposes!**
 
+import algorithm                    #For upperBound
+
 include "system/inclrtl"
 {.push debugger:off.}
 
@@ -155,14 +157,48 @@ 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`.
+proc rand*[T](r: var Rand; a: openArray[T]): T {.deprecated.} =
+  ## Returns a random element from the openarray `a`.
+  ## **Deprecated since v0.20.0:** use ``sample`` instead.
   result = a[rand(r, a.low..a.high)]
 
-proc rand*[T](a: openArray[T]): T =
+proc rand*[T: SomeInteger](t: typedesc[T]): T =
+  ## Returns a random integer in the range `low(T)..high(T)`.
+  result = cast[T](state.next)
+
+proc rand*[T](a: openArray[T]): T {.deprecated.} =
   ## returns a random element from the openarray `a`.
+  ## **Deprecated since v0.20.0:** use ``sample`` instead.
+  result = a[rand(a.low..a.high)]
+
+proc sample*[T](r: var Rand; a: openArray[T]): T =
+  ## returns a random element from openArray ``a`` using state in ``r``.
+  result = a[r.rand(a.low..a.high)]
+
+proc sample*[T](a: openArray[T]): T =
+  ## returns a random element from openArray ``a`` using non-thread-safe state.
   result = a[rand(a.low..a.high)]
 
+proc sample*[T, U](r: var Rand; a: openArray[T], cdf: openArray[U]): T =
+  ## Sample one element from openArray ``a`` when it has cumulative distribution
+  ## function (CDF) ``cdf`` (not necessarily normalized, any type of elements
+  ## convertible to ``float``). Uses state in ``r``. E.g.:
+  ##
+  ## .. code-block:: nim
+  ##   let val = [ "a", "b", "c", "d" ]  # some values
+  ##   var cnt = [1, 2, 3, 4]            # histogram of counts
+  ##   echo r.sample(val, cnt.cumsummed) # echo a sample
+  assert(cdf.len == a.len)              # Two basic sanity checks.
+  assert(float(cdf[^1]) > 0.0)
+  #While we could check cdf[i-1] <= cdf[i] for i in 1..cdf.len, that could get
+  #awfully expensive even in debugging modes.
+  let u = r.rand(float(cdf[^1]))
+  a[cdf.upperBound(U(u))]
+
+proc sample*[T, U](a: openArray[T], cdf: openArray[U]): T =
+  ## Like ``sample(var Rand; openArray[T], openArray[U])``, but uses default
+  ## non-thread-safe state.
+  state.sample(a, cdf)
 
 proc initRand*(seed: int64): Rand =
   ## Creates a new ``Rand`` state from ``seed``.
@@ -191,8 +227,12 @@ when not defined(nimscript):
   proc randomize*() {.benign.} =
     ## Initializes the random number generator with a "random"
     ## number, i.e. a tickcount. Note: Does not work for NimScript.
-    let now = times.getTime()
-    randomize(convert(Seconds, Nanoseconds, now.toUnix) + now.nanosecond)
+    when defined(js):
+      let time = int64(times.epochTime() * 1_000_000_000)
+      randomize(time)
+    else:
+      let now = times.getTime()
+      randomize(convert(Seconds, Nanoseconds, now.toUnix) + now.nanosecond)
 
 {.pop.}