From 95a1066b09af815ebf878c185ce0fde6f41330f2 Mon Sep 17 00:00:00 2001
From: Mitya Selivanov <0x7fffff@guattari.ru>
Date: Tue, 30 Aug 2022 09:32:53 +0400
Subject: Refactor

---
 source/kit/mersenne_twister_64.c | 37 +++++++++++++++++++++++--------------
 1 file changed, 23 insertions(+), 14 deletions(-)

(limited to 'source')

diff --git a/source/kit/mersenne_twister_64.c b/source/kit/mersenne_twister_64.c
index c8bbbe2..06f8535 100644
--- a/source/kit/mersenne_twister_64.c
+++ b/source/kit/mersenne_twister_64.c
@@ -2,6 +2,13 @@
 
 #include "time.h"
 
+enum {
+  MM       = 156,
+  MATRIX_A = 0xb5026f5aa96619e9ull,
+  UM       = 0xffffffff80000000ull,
+  LM       = 0x7fffffffull
+};
+
 void kit_mt64_init_array(kit_mt64_state_t *const state,
                          ptrdiff_t const         size,
                          uint64_t const *const   seed) {
@@ -21,29 +28,26 @@ void kit_mt64_init(kit_mt64_state_t *const state,
 }
 
 uint64_t kit_mt64_generate(kit_mt64_state_t *const state) {
-  static uint64_t const mag01[2] = { 0ull, 0xB5026F5AA96619E9ull };
+  static uint64_t const mag01[2] = { 0ull, MATRIX_A };
 
   int      i;
   uint64_t x;
 
   if (state->index >= KIT_MT64_N) {
-    for (i = 0; i < KIT_MT64_N - 156; i++) {
-      x = (state->mt[i] & 0xFFFFFFFF80000000ull) |
-          (state->mt[i + 1] & 0x7FFFFFFFull);
-      state->mt[i] = state->mt[i + 156] ^ (x >> 1u) ^
+    for (i = 0; i < KIT_MT64_N - MM; i++) {
+      x            = (state->mt[i] & UM) | (state->mt[i + 1] & LM);
+      state->mt[i] = state->mt[i + MM] ^ (x >> 1u) ^
                      mag01[(int) (x & 1ull)];
     }
 
     for (; i < KIT_MT64_N - 1; i++) {
-      x = (state->mt[i] & 0xFFFFFFFF80000000ull) |
-          (state->mt[i + 1] & 0x7FFFFFFFull);
-      state->mt[i] = state->mt[i + (156 - KIT_MT64_N)] ^ (x >> 1u) ^
+      x            = (state->mt[i] & UM) | (state->mt[i + 1] & LM);
+      state->mt[i] = state->mt[i + (MM - KIT_MT64_N)] ^ (x >> 1u) ^
                      mag01[(int) (x & 1ull)];
     }
 
-    x = (state->mt[KIT_MT64_N - 1] & 0xFFFFFFFF80000000ull) |
-        (state->mt[0] & 0x7FFFFFFFull);
-    state->mt[KIT_MT64_N - 1] = state->mt[156 - 1] ^ (x >> 1u) ^
+    x = (state->mt[KIT_MT64_N - 1] & UM) | (state->mt[0] & LM);
+    state->mt[KIT_MT64_N - 1] = state->mt[MM - 1] ^ (x >> 1u) ^
                                 mag01[(int) (x & 1ull)];
 
     state->index = 0;
@@ -52,19 +56,24 @@ uint64_t kit_mt64_generate(kit_mt64_state_t *const state) {
   x = state->mt[state->index++];
 
   x ^= (x >> 29u) & 0x5555555555555555ull;
-  x ^= (x << 17u) & 0x71D67FFFEDA60000ull;
-  x ^= (x << 37u) & 0xFFF7EEE000000000ull;
+  x ^= (x << 17u) & 0x71d67fffeda60000ull;
+  x ^= (x << 37u) & 0xfff7eee000000000ull;
   x ^= (x >> 43u);
 
   return x;
 }
 
 uint64_t kit_mt64_seed() {
+  static uint64_t n = 0;
+
   struct timespec t;
   timespec_get(&t, TIME_UTC);
 
+  uint64_t seed[2] = { (n++) ^ (uint64_t) t.tv_sec,
+                       (uint64_t) t.tv_nsec };
+
   kit_mt64_state_t s;
-  kit_mt64_init(&s, (uint64_t) t.tv_nsec);
+  kit_mt64_init_array(&s, sizeof seed / sizeof *seed, seed);
 
   return kit_mt64_generate(&s);
 }
-- 
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