switch to fastrand (not actually any faster)

combinators.nim

@@ -1,5 +1,5 @@
 import algorithm, random, sugar
-import fixedseq, game
+import fastrand, fixedseq, game
 
 
 proc nextPermutation(x: var FixedSeq): bool =
@@ -93,4 +93,4 @@ proc randomFuture*(dice: FixedSeq, r: var Rand): FixedSeq[5, Die, int8] =
   result.initFixedSeq
   let order = dice.dup(shuffle(r))
   for i, color in order:
-    result.add((color, r.rand(1..3)))
+    result.add((color, r.fastRand(1..3)))

fastrand.nim

@@ -0,0 +1,74 @@
+import random, math
+import times, std/monotimes, strformat, strutils
+
+
+proc formatNum(n: SomeNumber): string =
+  let s = $(n.round)
+  let t = s[0 .. s.len - 3]
+  var count = 1
+  for i in countdown(t.high, 0):
+    result.insert($t[i], 0)
+    if count mod 3 == 0 and i != 0:
+      result.insert(",", 0)
+    count += 1
+
+
+proc formatRate(n: Natural, d: Duration): string =
+  result = formatNum(1_000_000'f64 * n.float64 / d.inMicroseconds.float64)
+
+
+const upperBound = uint64(uint32.high)
+
+
+proc fastRand*[T: Natural](r: var Rand, x: T): T =
+  # Nim ranges are usually inclusive, but this algorithm is exclusive
+  let x = x.uint64 + 1
+  let num = if x <= upperBound:
+    ((r.next shr 32) * x.uint64) shr 32
+  else:
+    r.next mod x.uint64
+  result = T(num)
+
+
+proc fastRand*(r: var Rand; x, y: Natural): Natural =
+  let lim = (y - x)
+  result = fastRand(r, lim) + x
+
+
+proc fastRand*[T](r: var Rand, slice: HSlice[T, T]): T =
+  let n = fastRand(r, slice.a.Natural, slice.b.Natural)
+  result = T(n)
+
+
+proc testFastRand(num = 1_000_000_000): Duration =
+  var r = initRand(rand(int64))
+  let start = getMonoTime()
+  for i in 1 .. num:
+    discard r.fastRand(5)
+  result = getMonoTime() - start
+  # echo "fastrand execution rate: ",  1000 * num / dur.inMilliseconds.int, " generated per second."
+
+
+proc testStdRand(num = 1_000_000_000): Duration =
+  var r = initRand(rand(int64))
+  let start = getMonoTime()
+  for i in 1 .. num:
+    discard r.rand(4)
+  result = getMonoTime() - start
+  # echo "std rand execution rate: ", 1000 * num / dur.inMilliseconds.int, " generated per second."
+
+
+when isMainModule:
+  randomize()
+  var r = initRand(rand(int64))
+  let runs = 100_000_000
+  var totals: array[5..9, int]
+  for i in 1 .. runs:
+    let n = r.fastRand(5..9)
+    totals[n] += 1
+  echo totals
+
+  # let fr = testFastRand(runs)
+  # echo "fastrand execution rate: ", formatNum(1_000_000 * runs / fr.inMicroseconds.int)
+  # let sr = testStdRand(runs)
+  # echo "standard execution rate: ", formatNum(1_000_000 * runs / sr.inMicroseconds.int)