Add random() and srandom()

Closes #123

libc/rand/rand.h

@@ -6,7 +6,7 @@ COSMOPOLITAN_C_START_
 │ cosmopolitan § random                                                    ─╬─│┼
 ╚────────────────────────────────────────────────────────────────────────────│*/
 
-#define RAND_MAX __INT_MAX__              /* only applies to rand() */
+#define RAND_MAX __INT_MAX__ /* only applies to rand() */
 void srand(uint64_t) nothrow nocallback;  /* seeds rand() only      */
 int rand(void) nothrow nocallback;        /* ≥0 unseeded lcg prng   */
 uint32_t rand32(void) nothrow nocallback; /* random as possible rng */
@@ -25,6 +25,9 @@ int64_t winrandish(void);
 uint64_t rdrand(void);
 uint64_t rdseed(void);
 float randf(void);
+char *initstate(unsigned, char *, size_t);
+char *setstate(char *);
+long random(void);
 
 COSMOPOLITAN_C_END_
 #endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */

libc/rand/random.c

@@ -0,0 +1,128 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╚──────────────────────────────────────────────────────────────────────────────╝
+│                                                                              │
+│  Musl Libc                                                                   │
+│  Copyright © 2005-2014 Rich Felker, et al.                                   │
+│                                                                              │
+│  Permission is hereby granted, free of charge, to any person obtaining       │
+│  a copy of this software and associated documentation files (the             │
+│  "Software"), to deal in the Software without restriction, including         │
+│  without limitation the rights to use, copy, modify, merge, publish,         │
+│  distribute, sublicense, and/or sell copies of the Software, and to          │
+│  permit persons to whom the Software is furnished to do so, subject to       │
+│  the following conditions:                                                   │
+│                                                                              │
+│  The above copyright notice and this permission notice shall be              │
+│  included in all copies or substantial portions of the Software.             │
+│                                                                              │
+│  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,             │
+│  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF          │
+│  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.      │
+│  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY        │
+│  CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,        │
+│  TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE           │
+│  SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                      │
+│                                                                              │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/rand/rand.h"
+
+asm(".ident\t\"\\n\\n\
+Musl libc (MIT License)\\n\
+Copyright 2005-2014 Rich Felker, et. al.\"");
+asm(".include \"libc/disclaimer.inc\"");
+
+/*
+ * this code uses the same lagged fibonacci generator as the
+ * original bsd random implementation except for the seeding
+ * which was broken in the original
+ */
+
+static uint32_t init[] = {
+    0x00000000, 0x5851f42d, 0xc0b18ccf, 0xcbb5f646, 0xc7033129, 0x30705b04,
+    0x20fd5db4, 0x9a8b7f78, 0x502959d8, 0xab894868, 0x6c0356a7, 0x88cdb7ff,
+    0xb477d43f, 0x70a3a52b, 0xa8e4baf1, 0xfd8341fc, 0x8ae16fd9, 0x742d2f7a,
+    0x0d1f0796, 0x76035e09, 0x40f7702c, 0x6fa72ca5, 0xaaa84157, 0x58a0df74,
+    0xc74a0364, 0xae533cc4, 0x04185faf, 0x6de3b115, 0x0cab8628, 0xf043bfa4,
+    0x398150e9, 0x37521657,
+};
+
+static int n = 31;
+static int i = 3;
+static int j = 0;
+static uint32_t *x = init + 1;
+
+static uint32_t lcg31(uint32_t x) {
+  return (1103515245 * x + 12345) & 0x7fffffff;
+}
+
+static uint64_t lcg64(uint64_t x) {
+  return 6364136223846793005ull * x + 1;
+}
+
+static void *savestate(void) {
+  x[-1] = (n << 16) | (i << 8) | j;
+  return x - 1;
+}
+
+static void loadstate(uint32_t *state) {
+  x = state + 1;
+  n = x[-1] >> 16;
+  i = (x[-1] >> 8) & 0xff;
+  j = x[-1] & 0xff;
+}
+
+void srandom(unsigned seed) {
+  int k;
+  uint64_t s = seed;
+  if (!n) {
+    x[0] = s;
+    return;
+  }
+  i = n == 31 || n == 7 ? 3 : 1;
+  j = 0;
+  for (k = 0; k < n; k++) {
+    s = lcg64(s);
+    x[k] = s >> 32;
+  }
+  /* make sure x contains at least one odd number */
+  x[0] |= 1;
+}
+
+char *initstate(unsigned seed, char *state, size_t size) {
+  void *old;
+  if (size < 8) return 0;
+  old = savestate();
+  if (size < 32) {
+    n = 0;
+  } else if (size < 64) {
+    n = 7;
+  } else if (size < 128) {
+    n = 15;
+  } else if (size < 256) {
+    n = 31;
+  } else {
+    n = 63;
+  }
+  x = (uint32_t *)state + 1;
+  srandom(seed);
+  savestate();
+  return old;
+}
+
+char *setstate(char *state) {
+  void *old;
+  old = savestate();
+  loadstate((uint32_t *)state);
+  return old;
+}
+
+long random(void) {
+  long k;
+  if (!n) return (x[0] = lcg31(x[0]));
+  x[i] += x[j];
+  k = x[i] >> 1;
+  if (++i == n) i = 0;
+  if (++j == n) j = 0;
+  return k;
+}