On 2016-05-25 06:14, Qu Wenruo wrote:
> +void rand_seed(u64 seed)
> +{
> + int i;
> + /* only use the last 48 bits */
> + for (i = 0; i < 3; i++) {
> + seeds[i] = (unsigned short)(seed ^ (unsigned short)(-1));
> + seed >>= 16;
> + }
> + seed_initlized = 1;
> +}
> +
> +u32 rand_u32(void)
> +{
> + struct timeval tv;
> +
> + if (seed_initlized)
> + return nrand48(seeds);
> +
> + /*
> + * It's possible to use /dev/random, but we don't need that true
> + * random number nor want to wait for entropy,
> + * since we're only using random API to do corruption to test.
> + * Time and pid/ppid based seed would be good enough, and won't
> + * cause sleep for entropy pool.
> + */
> + gettimeofday(&tv, 0);
> + seeds[0] = getpid() ^ (tv.tv_sec & 0xFFFF);
> + seeds[1] = getppid() ^ (tv.tv_usec & 0xFFFF);
> + seeds[2] = (tv.tv_sec ^ tv.tv_usec) >> 16;
> + seed_initlized = 1;
> +
> + return (u32)nrand48(seeds);
> +}
Just for my curiosity, which is the advantage of rand48() respect to rand() if we utilize only the lower 32 bit ? It wouldn't be more simple to use:
#define rand_seed(x) srand((int)(x))
/*
* NOTE: not for cryptographic use
*/
u32 rand_u32(void)
{
static __thread int initialized = 0;
if (!initialized) {
struct timeval tv;
gettimeofday(&tv, 0);
rand_seed(tv.tv_usec | (tv.tv_sec ^ getpid() ^ getppid()) << 16);
initialized = 1;
}
return (u32)rand();
}
this in order to avoid the mess of the 48 bit ?
BR
G.Baroncelli
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