sim_seed.h File Reference

Seed derivation helpers for deterministic RNG streams. More...

#include <stdint.h>

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Macros
#define	SIM_SEED_DEFAULT   0xA5A5A5A5A5A5A5A5ULL

Functions
uint64_t	sim_seed_normalize (uint64_t seed)
	Normalize a seed (zero maps to SIM_SEED_DEFAULT).
uint64_t	sim_seed_mix64 (uint64_t value)
	Mix a 64-bit value into a high-quality hash.
uint64_t	sim_seed_tag (const char *tag)
	Hash a domain tag into a 64-bit value.
uint64_t	sim_seed_derive (uint64_t base_seed, uint64_t tag_hash, uint64_t index)
	Derive a deterministic seed from a base seed, tag hash, and index.
void	sim_seed_stream (uint64_t base_seed, const char *tag, uint64_t index, uint64_t *out_state, uint64_t *out_inc)
	Derive a PCG32 stream (state + increment) from a base seed and domain tag.

Detailed Description

Seed derivation helpers for deterministic RNG streams.

Macro Definition Documentation

SIM_SEED_DEFAULT

#define SIM_SEED_DEFAULT   0xA5A5A5A5A5A5A5A5ULL

Default base seed used when a caller provides zero.

Function Documentation

sim_seed_derive()

uint64_t sim_seed_derive	(	uint64_t	base_seed,
		uint64_t	tag_hash,
		uint64_t	index
	)

Derive a deterministic seed from a base seed, tag hash, and index.

Parameters

base_seed	Base seed; zero is normalized to SIM_SEED_DEFAULT.
tag_hash	Domain tag hash, often from sim_seed_tag().
index	Numeric substream index.

Returns

Derived child seed.

sim_seed_mix64()

uint64_t sim_seed_mix64

(

uint64_t

value

)

Mix a 64-bit value into a high-quality hash.

Parameters

value

Input value.

Returns

Mixed 64-bit value suitable for stream derivation.

sim_seed_normalize()

uint64_t sim_seed_normalize

(

uint64_t

seed

)

Normalize a seed (zero maps to SIM_SEED_DEFAULT).

Parameters

seed	Caller-provided seed.

Returns

seed when nonzero, otherwise SIM_SEED_DEFAULT.

sim_seed_stream()

void sim_seed_stream	(	uint64_t	base_seed,
		const char *	tag,
		uint64_t	index,
		uint64_t *	out_state,
		uint64_t *	out_inc
	)

Derive a PCG32 stream (state + increment) from a base seed and domain tag.

Parameters

	base_seed	Base seed; zero is normalized to SIM_SEED_DEFAULT.
	tag	Null-terminated domain tag for stream separation.
	index	Numeric substream index.
[out]	out_state	Receives the PCG state when non-NULL.
[out]	out_inc	Receives the PCG increment when non-NULL.

sim_seed_tag()

uint64_t sim_seed_tag

(

const char *

tag

)

Hash a domain tag into a 64-bit value.

Parameters

tag	Null-terminated tag; NULL hashes as an empty tag.

Returns

Deterministic 64-bit tag hash.