pcg_rnd.c

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// code for temporal network SIR by Petter Holme (2018)

// this file contains the random number generator, derived from the PCG
// RNG v0.94 http://www.pcg-random.org under the Apache License 2.0
// http://www.apache.org/licenses/LICENSE-2.0

// 32-bit Output, 64-bit State, the PCG-XSH-RR version

#include "tsir.h"

extern GLOBALS g;

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uint32_t pcg_32 () {
	uint64_t state = g.state;
	uint32_t value, rot;

	g.state = g.state * 6364136223846793005ull + 1442695040888963407ull;
	value = ((state >> 18u) ^ state) >> 27u;
	rot = state >> 59u;
	return (value >> rot) | (value << ((- rot) & 31u));
}

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uint32_t pcg_32_bounded (uint32_t bound) {
	uint32_t threshold = -bound % bound, r;

	do r = pcg_32();
	while (r < threshold);
	
	return r % bound;
}

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uint16_t pcg_16 () {
	static uint32_t exist, rmem;

	if (exist) {
		exist = 0;
		return rmem >> 16;
	}
	exist = 1;
	rmem = pcg_32();
	return rmem;
}

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