From 116e478a7d945f2012408c4d76fc9badbb257cd4 Mon Sep 17 00:00:00 2001
From: siddharth <s@ricketyspace.net>
Date: Tue, 17 Aug 2021 20:15:17 -0400
Subject: lib: add MTRand type and methods
This is going to replace MTSeed and MTExtract functions.
---
lib/rng.go | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 50 insertions(+)
(limited to 'lib')
diff --git a/lib/rng.go b/lib/rng.go
index 7e7611e..6f57324 100644
--- a/lib/rng.go
+++ b/lib/rng.go
@@ -19,6 +19,13 @@ var mtCoefL uint32 = 18
var mtF uint32 = 1812433253
+// MT19937 instance struct
+type MTRand struct {
+ genSt [624]uint32
+ index uint32
+ initialized bool
+}
+
// Stores state of MT19937 generator.
var mtGenSt []uint32 = make([]uint32, mtCoefN)
var mtIndex uint32 = mtCoefN + 1
@@ -26,6 +33,16 @@ var mtIndex uint32 = mtCoefN + 1
var mtLowerMask uint32 = (1 << mtCoefR) - 1
var mtUpperMask uint32 = 0xFFFFFFFF & (^mtLowerMask)
+func (r *MTRand) Seed(s uint32) {
+ r.index = mtCoefN
+ r.genSt[0] = s
+ for i := uint32(1); i < mtCoefN; i++ {
+ r.genSt[i] = (0xFFFFFFFF &
+ (mtF*(r.genSt[i-1]^(r.genSt[i-1]>>(mtCoefW-2))) + i))
+ }
+ r.initialized = true
+}
+
func MTSeed(seed uint32) {
mtIndex = mtCoefN
mtGenSt[0] = seed
@@ -35,6 +52,26 @@ func MTSeed(seed uint32) {
}
}
+func (r *MTRand) Extract() uint32 {
+ if !r.initialized || r.index >= mtCoefN {
+ if !r.initialized {
+ r.Seed(5489)
+ }
+ r.twist()
+ }
+
+ y := r.genSt[r.index]
+ y = y ^ ((y >> mtCoefU) & mtCoefD)
+ y = y ^ ((y << mtCoefS) & mtCoefB)
+ y = y ^ ((y << mtCoefT) & mtCoefC)
+ y = y ^ (y >> mtCoefL)
+
+ r.index = r.index + 1
+
+ y = 0xFFFFFFFF & y
+ return y
+}
+
func MTExtract() uint32 {
if mtIndex >= mtCoefN {
if mtIndex > mtCoefN {
@@ -55,6 +92,19 @@ func MTExtract() uint32 {
return r
}
+func (r *MTRand) twist() {
+ for i := uint32(0); i < mtCoefN-1; i++ {
+ x := (r.genSt[i] & mtUpperMask) +
+ (r.genSt[(i+1)%mtCoefN] & mtLowerMask)
+ xA := x >> 1
+ if x%2 != 0 { // lowest bit of x is 1
+ xA = xA ^ mtCoefA
+ }
+ r.genSt[i] = r.genSt[(i+mtCoefM)%mtCoefN] ^ xA
+ }
+ r.index = 0
+}
+
func mtTwist() {
for i := uint32(0); i < mtCoefN-1; i++ {
x := (mtGenSt[i] & mtUpperMask) +
--
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