Re: [PATCH 2/7] lib/random32.c: Remove excess calls to prandom_u32_state in initialization

Daniel Borkmann
2014-06-08T12:11:16Z

On 06/07/2014 10:20 AM, George Spelvin wrote:
> Unrolling code in single-use code paths is just silly. There are two
> instances:
>
> 1) prandom_warmup() calls 10 times.
> 2) prandom_state_selftest() can avoid one call and simplify the
> loop logic by repeating an assignment to a local variable
> (that probably adds zero code anyway)
>
> Signed-off-by: George Spelvin <linux@horizon.com>

Fine by me although we simply resembled initialization code from
GSL here. I think that your subject line is a bit misleading though.

> ---
> lib/random32.c | 21 ++++++++-------------
> 1 file changed, 8 insertions(+), 13 deletions(-)
>
> diff --git a/lib/random32.c b/lib/random32.c
> index 4da5d281..2e7c15c0 100644
> --- a/lib/random32.c
> +++ b/lib/random32.c
> @@ -134,17 +134,11 @@ EXPORT_SYMBOL(prandom_bytes);
>
> static void prandom_warmup(struct rnd_state *state)
> {
> + int i;
> +
> /* Calling RNG ten times to satify recurrence condition */
> - prandom_u32_state(state);
> - prandom_u32_state(state);
> - prandom_u32_state(state);
> - prandom_u32_state(state);
> - prandom_u32_state(state);
> - prandom_u32_state(state);
> - prandom_u32_state(state);
> - prandom_u32_state(state);
> - prandom_u32_state(state);
> - prandom_u32_state(state);
> + for (i = 0; i < 10; i++)
> + prandom_u32_state(state);
> }
>
> static void prandom_seed_very_weak(struct rnd_state *state, u32 seed)
> @@ -433,14 +427,15 @@ static void __init prandom_state_selftest(void)
>
> for (i = 0; i < ARRAY_SIZE(test2); i++) {
> struct rnd_state state;
> + u32 result;
>
> prandom_seed_very_weak(&state, test2[i].seed);
> prandom_warmup(&state);
>
> - for (j = 0; j < test2[i].iteration - 1; j++)
> - prandom_u32_state(&state);
> + for (j = 0; j < test2[i].iteration; j++)
> + result = prandom_u32_state(&state);
>
> - if (test2[i].result != prandom_u32_state(&state))
> + if (test2[i].result != result)
> errors++;
>
> runs++;
>