From 20a34ca17f0cc68c42952c0a2eb767942e39e2d9 Mon Sep 17 00:00:00 2001
From: Richard Brooksby <rb@ravenbrook.com>
Date: Sat, 19 Mar 2016 08:57:27 +0000
Subject: [PATCH] Importing good random number generator from testlib for use
 in quicksort and perhaps later in cuckoo hashing.

Copied from Perforce
 Change: 190191
 ServerID: perforce.ravenbrook.com
---
 mps/code/mpm.c | 36 +++++++++++++++++++++++++++++++++---
 mps/code/mpm.h |  3 +++
 2 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/mps/code/mpm.c b/mps/code/mpm.c
index d2c87d5038d..7d944ae57eb 100644
--- a/mps/code/mpm.c
+++ b/mps/code/mpm.c
@@ -645,6 +645,38 @@ Bool StringEqual(const char *s1, const char *s2)
 }
 
 
+/* Random -- a random number generator
+ *
+ * TODO: This is a copy of the generator from testlib.c, which has
+ * extensive notes and verification tests.  The notes need to go to a
+ * design document, and the tests to a test.
+ */
+
+static unsigned RandomSeed = 1;
+#define Random_m 2147483647UL
+#define Random_a 48271UL
+unsigned Random32(void)
+{
+  AVER(UINT_MAX >= 4294967295U);
+  /* requires m == 2^31-1, a < 2^16 */
+  unsigned bot = Random_a * (RandomSeed & 0x7FFF);
+  unsigned top = Random_a * (RandomSeed >> 15);
+  RandomSeed = bot + ((top & 0xFFFF) << 15) + (top >> 16);
+  if (RandomSeed > Random_m)
+    RandomSeed -= Random_m;
+  return RandomSeed;
+}
+
+Word RandomWord(void)
+{
+  Word word;
+  Index i;
+  for (i = 0; i < MPS_WORD_WIDTH; i += 31)
+    word = (word << 31) | Random32();
+  return word;
+}
+
+
 /* QuickSort -- non-recursive bounded sort
  *
  * We can't rely on the standard library's qsort, which might have
@@ -669,7 +701,6 @@ static Bool quickSorted(void *array[], Count length,
 void QuickSort(void *array[], Count length,
                QuickSortCompare compare, void *closure)
 {
-  static Index seed = 0x6A9D03;
   struct {
     Index left, right;
   } stack[MPS_WORD_WIDTH];
@@ -683,8 +714,7 @@ void QuickSort(void *array[], Count length,
   for (;;) {
     while (right - left > 1) { /* no need to sort */
       /* Pick a random pivot. */
-      pivot = array[left + seed % (right - left)];
-      seed = seed * 69069 + 1;
+      pivot = array[left + RandomWord() % (right - left)];
 
       /* Hoare partition: scan from lo to hi, dividing it into elements
          less than the pivot and elements greater or equal. */
diff --git a/mps/code/mpm.h b/mps/code/mpm.h
index 01158fb0779..96f28ffc840 100644
--- a/mps/code/mpm.h
+++ b/mps/code/mpm.h
@@ -171,6 +171,9 @@ extern Res WriteF_firstformat_v(mps_lib_FILE *stream, Count depth,
 extern size_t StringLength(const char *s);
 extern Bool StringEqual(const char *s1, const char *s2);
 
+extern unsigned Random32(void);
+extern Word RandomWord(void);
+
 typedef Compare QuickSortCompare(void *left, void *right,
                                  void *closure);
 extern void QuickSort(void *array[], Count length,