Re: [kvm-unit-tests PATCH 1/5] lib: Add pseudo random functions

[Andrew Jones <andrew.jones@linux.dev>]

On Wed, Dec 13, 2023 at 01:49:38PM +0100, Nina Schoetterl-Glausch wrote:
> Add functions for generating pseudo random 32 and 64 bit values.
> The implementation is very simple and the randomness likely not
> of high quality.
> 
> Signed-off-by: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
> ---
>  Makefile       |  1 +
>  lib/libcflat.h |  7 +++++++
>  lib/rand.c     | 19 +++++++++++++++++++
>  3 files changed, 27 insertions(+)
>  create mode 100644 lib/rand.c
> 
> diff --git a/Makefile b/Makefile
> index 602910dd..7997e035 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -28,6 +28,7 @@ cflatobjs := \
>  	lib/printf.o \
>  	lib/string.o \
>  	lib/abort.o \
> +	lib/rand.o \
>  	lib/report.o \
>  	lib/stack.o
>  
> diff --git a/lib/libcflat.h b/lib/libcflat.h
> index 700f4352..ed947f98 100644
> --- a/lib/libcflat.h
> +++ b/lib/libcflat.h
> @@ -83,6 +83,13 @@ extern void abort(void) __attribute__((noreturn));
>  extern long atol(const char *ptr);
>  extern char *getenv(const char *name);
>  
> +typedef struct {
> +	uint32_t val;
> +} rand_state;
> +#define RAND_STATE_INIT(x) ((rand_state){ .val = (x) })
> +uint32_t rand32(rand_state *state);
> +uint64_t rand64(rand_state *state);
> +
>  extern int printf(const char *fmt, ...)
>  					__attribute__((format(printf, 1, 2)));
>  extern int snprintf(char *buf, int size, const char *fmt, ...)
> diff --git a/lib/rand.c b/lib/rand.c
> new file mode 100644
> index 00000000..658c4cbf
> --- /dev/null
> +++ b/lib/rand.c
> @@ -0,0 +1,19 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * pseudo random functions
> + *
> + * Copyright IBM Corp. 2023
> + */
> +
> +#include "libcflat.h"
> +
> +uint32_t rand32(rand_state *state)
> +{
> +	state->val = 0x915f77f5 * state->val + 1;
> +	return state->val ^ (state->val >> 16);
> +}
> +
> +uint64_t rand64(rand_state *state)
> +{
> +	return (uint64_t)rand32(state) << 32 | rand32(state);
> +}
> -- 
> 2.41.0
>

Alex Bennée posted a prng patch a long time ago that never got merged.

https://www.spinics.net/lists/kvm-arm/msg50921.html

would it be better to merge that?

Thanks,
drew