From fe18d8f4700438c2589978043f2fcaa45f651336 Mon Sep 17 00:00:00 2001
From: Troels Henriksen <athas@sigkill.dk>
Date: Fri, 10 Apr 2020 10:07:45 +0200
Subject: [PATCH] Add PCG32 implementation of the RANDOM signature.

---
 lib/github.com/diku-dk/sml-random/Pcg32.sml  | 64 ++++++++++++++++++++
 lib/github.com/diku-dk/sml-random/random.mlb |  1 +
 2 files changed, 65 insertions(+)
 create mode 100644 lib/github.com/diku-dk/sml-random/Pcg32.sml

diff --git a/lib/github.com/diku-dk/sml-random/Pcg32.sml b/lib/github.com/diku-dk/sml-random/Pcg32.sml
new file mode 100644
index 0000000..fcde67d
--- /dev/null
+++ b/lib/github.com/diku-dk/sml-random/Pcg32.sml
@@ -0,0 +1,64 @@
+(* Random numbers with PCG32 *)
+
+structure Pcg32 : RANDOM =
+  struct
+
+    val pcg32mult = 0wx5851f42d4c957f2d
+
+    type generator = {state: Word64.word ref, inc: Word64.word ref}
+
+    fun mask32 x = Word64.andb (x, 0wxFFFFFFFF)
+
+    fun nextWord32 {state, inc} =
+        let val oldstate = !state
+            val xorshifted =
+                mask32 (Word64.>>(Word64.xorb(Word64.>>(oldstate, 0w18),
+                                              oldstate),
+                                  0w27));
+            val rot = mask32(Word64.>>(oldstate, 0w59))
+            val x = Word64.orb(Word64.>>(xorshifted, Word.fromLarge rot),
+                               (Word64.<<(xorshifted,
+                                          Word.fromLarge(Word64.andb(Word64.+(Word64.notb rot, 0w1),
+                                                                     0w31)))))
+        in state := oldstate * pcg32mult + !inc;
+           Word32.fromLarge(mask32(x))
+        end
+
+    fun newgenseed (seed: real) =
+        let val initstate = Word64.fromInt (trunc seed)
+            val initseq = 0w1
+            val state = ref 0w0
+            val inc = ref (Word64.orb (Word64.* (initseq, 0w2), 0w1))
+            val rng = {state=state,
+                       inc= inc}
+        in nextWord32 rng;
+           state := (!state + initstate);
+           nextWord32 rng;
+           rng
+        end
+
+    fun newgen () =
+        newgenseed (Time.toReal(Time.now()))
+
+    fun random rng =
+        Real.fromLargeInt (Word32.toLargeInt (nextWord32 rng)) / 4294967295.0
+
+    fun randomlist (n, rng) =
+      let fun h 0 res = res
+	    | h i res = h (i-1) (random rng :: res)
+      in h n []
+      end
+
+    fun range (min, max) =
+      if min >= max then raise Fail "Pcg32.range: empty range"
+      else fn rng => floor (real min + random rng * real (max-min))
+
+    fun rangelist (min, max) =
+      if min >= max then raise Fail "Pcg32.rangelist: empty range"
+      else fn (n, rng) =>
+	   let fun h 0 res = res
+		 | h i res = h (i-1) (floor (real min + random rng * real (max-min)) :: res)
+	   in h n []
+	   end
+
+  end
diff --git a/lib/github.com/diku-dk/sml-random/random.mlb b/lib/github.com/diku-dk/sml-random/random.mlb
index 3876dac..82b40f9 100644
--- a/lib/github.com/diku-dk/sml-random/random.mlb
+++ b/lib/github.com/diku-dk/sml-random/random.mlb
@@ -1,4 +1,5 @@
 local $(SML_LIB)/basis/basis.mlb
 in RANDOM.sig
    Random.sml
+   Pcg32.sml
 end