Avoid use of rand()

1 files changed, 59 insertions, 0 deletions

diff --git a/test/test_data.h b/test/test_data.h
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+/*
+  Copyright 2011-2021 David Robillard <d@drobilla.net>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THIS SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+#ifndef ZIX_TEST_DATA_H
+#define ZIX_TEST_DATA_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+/// Linear Congruential Generator for making random 32-bit integers
+static inline uint32_t
+lcg32(const uint32_t i)
+{
+  static const uint32_t a = 134775813u;
+  static const uint32_t c = 1u;
+
+  return (a * i) + c;
+}
+
+/// Linear Congruential Generator for making random 64-bit integers
+static inline uint64_t
+lcg64(const uint64_t i)
+{
+  static const uint64_t a = 6364136223846793005ull;
+  static const uint64_t c = 1ull;
+
+  return (a * i) + c;
+}
+
+/// Return a pseudo-pseudo-pseudo-random-ish integer with no duplicates
+static inline size_t
+unique_rand(size_t i)
+{
+  i ^= 0x5CA1AB1Eu; // Juggle bits to avoid linear clumps
+
+  // Largest prime < 2^32 which satisfies (2^32 = 3 mod 4)
+  static const size_t prime = 4294967291u;
+  if (i >= prime) {
+    return i; // Values >= prime are mapped to themselves
+  }
+
+  const size_t residue = ((uint64_t)i * i) % prime;
+  return (i <= prime / 2) ? residue : prime - residue;
+}
+
+#endif // ZIX_TEST_DATA_H