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PRNG(9) FreeBSD Kernel Developer's Manual PRNG(9)
NAME
prng - Kernel pseudo-random number generators
SYNOPSIS
#include <sys/prng.h>
uint32_t
prng32(void);
uint32_t
prng32_bounded(uint32_t bound);
uint64_t
prng64(void);
uint64_t
prng64_bounded(uint64_t bound);
DESCRIPTION
GENERIC PRNG ROUTINES
prng is a family of fast, non-cryptographic pseudo-random number
generators. Unlike random(9), prng32(), prng32_bounded(), prng64(), and
prng64_bounded() avoid shared global state, removing unnecessary
contention on SMP systems. The routines are not explicitly tied to any
specific implementation, and may produce different specific sequences on
different hosts, reboots, or versions of FreeBSD. Different CPUs in SMP
systems are guaranteed to produce different sequences of integers.
For cryptographically secure random numbers generated by the random(4)
kernel cryptographically secure random number generator subsystem, see
arc4random(9).
prng32()
Generate a 32-bit integer uniformly distributed in [0, 2^32-1].
prng32_bounded(bound)
Generate an integer uniformly in the range [0, bound-1].
prng64()
Generate a 64-bit integer uniformly distributed in [0, 2^64-1].
prng64_bounded(bound)
Generate an integer uniformly in the range [0, bound-1].
These routines are not reentrant; they are not safe to use in interrupt
handlers ("interrupt filters" in bus_setup_intr(9) terminology). They
are safe to use in all other kernel contexts, including interrupt threads
("ithreads").
REPRODUCIBLE PRNG APIS
In addition to these per-CPU helpers, the <sys/prng.h> header also
exposes the entire API of the PCG family of PRNGs as inline functions.
The PCG-C API is described in full at
https://www.pcg-random.org/using-pcg-c.html.
HISTORY
prng was introduced in FreeBSD 13.