From 91a686d1f5fac8b0992eba17db94d3c8f76cdc65 Mon Sep 17 00:00:00 2001
From: Bill Currie <bill@taniwha.org>
Date: Wed, 22 Dec 2021 00:01:26 +0900
Subject: [PATCH] [util] Add mtwist float random number functions

mtwist_rand_0_1 produces numbers in the range [0, 1) and
mtwist_rand_m1_1 produces numbers in the range (-1, 1). The numbers will
not be denormal, so the distribution should be fairly uniform (as much
as Mersenne Twister itself is), but this needs proper testing.

0 is included for the mtwist_rand_0_1 as it seems useful, but -1 is not
included in mtwist_rand_m1_1 in order to keep the extremes of the
distribution balanced around 0.
---
 include/QF/mersenne.h | 40 ++++++++++++++++++++++++++++++++++++++++
 libs/util/mersenne.c  |  1 +
 2 files changed, 41 insertions(+)

diff --git a/include/QF/mersenne.h b/include/QF/mersenne.h
index 197ded28d..d80b53e43 100644
--- a/include/QF/mersenne.h
+++ b/include/QF/mersenne.h
@@ -42,5 +42,45 @@ typedef struct {
 
 void mtwist_seed (mtstate_t *state, uint32_t seed);
 uint32_t mtwist_rand (mtstate_t *state);
+GNU89INLINE inline float mtwist_rand_0_1 (mtstate_t *state);
+GNU89INLINE inline float mtwist_rand_m1_1 (mtstate_t *state);
+
+#ifndef IMPLEMENT_MTWIST_Funcs
+GNU89INLINE inline
+#else
+VISIBLE
+#endif
+float
+mtwist_rand_0_1 (mtstate_t *state)
+{
+	union {
+		uint32_t    u;
+		float       f;
+	}           uf;
+
+	uf.u = mtwist_rand (state) & 0x007fffff;
+	uf.u |= 0x3f800000;
+	return uf.f - 1.0;
+}
+
+#ifndef IMPLEMENT_MTWIST_Funcs
+GNU89INLINE inline
+#else
+VISIBLE
+#endif
+float
+mtwist_rand_m1_1 (mtstate_t *state)
+{
+	union {
+		uint32_t    u;
+		float       f;
+	}           uf;
+
+	do {
+		uf.u = mtwist_rand (state) & 0x007fffff;
+	} while (!uf.u);
+	uf.u |= 0x40000000;
+	return uf.f - 3.0;
+}
 
 #endif//__QF_mersenne_h
diff --git a/libs/util/mersenne.c b/libs/util/mersenne.c
index 35794932b..5c0cbacbc 100644
--- a/libs/util/mersenne.c
+++ b/libs/util/mersenne.c
@@ -48,6 +48,7 @@
 	There were no differences.
 */
 
+#define IMPLEMENT_MTWIST_Funcs
 #include "QF/mersenne.h"
 
 #define KNUTH_MULT		1812433253ul	// 0x6c078965