From 0a809645da4141e026867f6e0d81c71f02f1bc4e Mon Sep 17 00:00:00 2001
From: KunoiSayami <i@leanhe.dev>
Date: Fri, 5 Nov 2021 17:08:00 +0800
Subject: test: Add arena_test

Signed-off-by: KunoiSayami <i@leanhe.dev>
---
 headers/random.h | 57 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)
 create mode 100644 headers/random.h

(limited to 'headers/random.h')

diff --git a/headers/random.h b/headers/random.h
new file mode 100644
index 0000000..2b04757
--- /dev/null
+++ b/headers/random.h
@@ -0,0 +1,57 @@
+#ifndef CLEVELDB_RANDOM_H
+#define CLEVELDB_RANDOM_H
+#include <cstdint>
+
+namespace cleveldb {
+
+// A very simple random number generator.  Not especially good at
+// generating truly random bits, but good enough for our needs in this
+// package.
+	class Random {
+	private:
+		uint32_t seed_;
+
+	public:
+		explicit Random(uint32_t s) : seed_(s & 0x7fffffffu) {
+			// Avoid bad seeds.
+			if (seed_ == 0 || seed_ == 2147483647L) {
+				seed_ = 1;
+			}
+		}
+		uint32_t Next() {
+			static const uint32_t M = 2147483647L;  // 2^31-1
+			static const uint64_t A = 16807;        // bits 14, 8, 7, 5, 2, 1, 0
+			// We are computing
+			//       seed_ = (seed_ * A) % M,    where M = 2^31-1
+			//
+			// seed_ must not be zero or M, or else all subsequent computed values
+			// will be zero or M respectively.  For all other values, seed_ will end
+			// up cycling through every number in [1,M-1]
+			uint64_t product = seed_ * A;
+
+			// Compute (product % M) using the fact that ((x << 31) % M) == x.
+			seed_ = static_cast<uint32_t>((product >> 31) + (product & M));
+			// The first reduction may overflow by 1 bit, so we may need to
+			// repeat.  mod == M is not possible; using > allows the faster
+			// sign-bit-based test.
+			if (seed_ > M) {
+				seed_ -= M;
+			}
+			return seed_;
+		}
+		// Returns a uniformly distributed value in the range [0..n-1]
+		// REQUIRES: n > 0
+		uint32_t Uniform(int n) { return Next() % n; }
+
+		// Randomly returns true ~"1/n" of the time, and false otherwise.
+		// REQUIRES: n > 0
+		bool OneIn(int n) { return (Next() % n) == 0; }
+
+		// Skewed: pick "base" uniformly from range [0,max_log] and then
+		// return "base" random bits.  The effect is to pick a number in the
+		// range [0,2^max_log-1] with exponential bias towards smaller numbers.
+		uint32_t Skewed(int max_log) { return Uniform(1 << Uniform(max_log + 1)); }
+	};
+
+}  // namespace cleveldb
+#endif //CLEVELDB_RANDOM_H
-- 
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