xorshift

.gitignore

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+obj_dir

COPYING

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+Copyright 2024 Peter McGoron
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions
+are met:
+
+1. Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+
+2. Redistributions in binary form must reproduce the above copyright
+notice, this list of conditions and the following disclaimer in the
+documentation and/or other materials provided with the distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+“AS IS” AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
+TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

Makefile

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+VERILATOR_FLAGS = --cc --exe -x-assign fast -Wall
+VERILATOR_INPUT = xorshift.v xorshift.cpp
+
+obj_dir/Vxorshift: obj_dir/Vxorshift.mk obj_dir/Vxorshift.cpp \
+                   obj_dir/Vxorshift.h xorshift.cpp
+	cd obj_dir && make -f Vxorshift.mk && ./Vxorshift
+obj_dir/Vxorshift.mk: $(VERILATOR_INPUT)
+	verilator $(VERILATOR_FLAGS) $(VERILATOR_INPUT)
+clean:
+	rm -rf obj_dir

README.rst

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+------------
+verilog_rand
+------------
+
+Random number generators in verilog. BSD 2-clause.
+
+-----------
+XORShift-64
+-----------
+
+XORShift-64 is a pseudo-RNG with a period of ``2^64-1``.
+At 100 MHz it would take centuries before the RNG repeats.

xorshift.cpp

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+/*
+ * Copyright 2024 Peter McGoron
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * “AS IS” AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
+ * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
+#include <memory>
+#include <limits>
+#include <cstdint>
+#include <iostream>
+#include <verilated.h>
+#include "Vxorshift.h"
+
+Vxorshift *mod;
+
+static void run_clock() {
+	mod->clk = !mod->clk;
+	mod->eval();
+
+	mod->clk = !mod->clk;
+	mod->eval();
+}
+
+static uint64_t xorshift_64() {
+	static uint64_t state = 88172645463325252LL;
+	state ^= state << 13;
+	state ^= state >> 7;
+	return state ^= state << 17;
+}
+
+int main(int argc, char **argv) {
+	Verilated::commandArgs(argc, argv);
+	mod = new Vxorshift;
+
+	mod->clk = 0;
+	mod->eval();
+
+	for (int i = 0; i < 100000; i++) {
+		uint64_t correct = xorshift_64();
+		run_clock();
+		if (correct != mod->data) {
+			std::cout << i << " " << correct << "!=" << mod->data << std::endl;
+		}
+	}
+
+	mod->final();
+
+	delete mod;
+
+	return 0;
+}

xorshift.v

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+/*
+ * Copyright 2024 Peter McGoron
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * “AS IS” AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
+ * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
+module xorshift (
+	input clk,
+	output [64-1:0] data
+);
+
+reg [64-1:0] state = 64'd88172645463325252;
+assign data = state;
+
+always @ (posedge clk) begin
+`define X_1 (state ^ (state << 13))
+`define X_2 (`X_1 ^ (`X_1 >> 7))
+	state <= (`X_2 ^ (`X_2 << 17));
+end
+
+endmodule