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.Dd August 5, 2020 .Dt PRNG 9 .Os .Sh NAME .Nm prng .Nd "Kernel pseudo-random number generators" .Sh SYNOPSIS n sys/prng.h .Ft uint32_t .Fn prng32 void .Ft uint32_t .Fn prng32_bounded "uint32_t bound" .Ft uint64_t .Fn prng64 void .Ft uint64_t .Fn prng64_bounded "uint64_t bound" .Sh DESCRIPTION .Ss GENERIC PRNG ROUTINES .Nm is a family of fast, .Em non-cryptographic pseudo-random number generators. Unlike .Xr random 9 , .Fn prng32 , .Fn prng32_bounded , .Fn prng64 , and .Fn 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 .Fx . Different CPUs in SMP systems are guaranteed to produce different sequences of integers.
p For .Em cryptographically secure random numbers generated by the .Xr random 4 kernel cryptographically secure random number generator subsystem, see .Xr arc4random 9 .
p l -tag -width indent t Fn prng32 Generate a 32-bit integer uniformly distributed in [0, 2^32-1]. t Fn prng32_bounded bound Generate an integer uniformly in the range [0, bound-1]. t Fn prng64 Generate a 64-bit integer uniformly distributed in [0, 2^64-1]. t Fn prng64_bounded bound Generate an integer uniformly in the range [0, bound-1]. .El
p These routines are not reentrant; they are not safe to use in interrupt handlers ("interrupt filters" in .Xr bus_setup_intr 9 terminology). They are safe to use in all other kernel contexts, including interrupt threads ("ithreads"). .Ss REPRODUCIBLE PRNG APIS In addition to these per-CPU helpers, the n 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 .Lk https://www.pcg-random.org/using-pcg-c.html . .Sh HISTORY .Nm was introduced in .Fx 13 .