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Merge pull request #15239 from benpicco/sys/luid-tweak

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sys/luid: improve luid_base() algorithm
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benpicco 2020-10-19 09:55:33 +02:00 committed by GitHub
commit fdc201a299
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1 changed files with 13 additions and 27 deletions
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40
sys/luid/luid.c
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@ -26,8 +26,17 @@
#include "luid.h"
#ifndef MAX
#define MAX(a, b) (((a) > (b)) ? (a) : (b))
#if CPUID_LEN
/* based on DJB2 Hash */
static void _luid_round(const uint8_t *in, size_t in_len, uint8_t *out, size_t out_len)
{
uint32_t hash = 5381;
for (size_t i = 0; i < in_len; i++) {
hash = hash * 33 + in[i];
out[i % out_len] ^= hash;
}
}
#endif
void __attribute__((weak)) luid_base(void *buf, size_t len)
@ -35,34 +44,11 @@ void __attribute__((weak)) luid_base(void *buf, size_t len)
memset(buf, LUID_BACKUP_SEED, len);
#if CPUID_LEN
uint8_t *out = buf;
uint8_t cid[CPUID_LEN];
uint8_t sum = 0;
cpuid_get(cid);
/* CPU ID is XORed with LUID_BACKUP_SEED.
* Then Fisher–Yates shuffle is performed to mix
* the bytes, as often large continuous chunks of
* CPU ID are equal on machines with the same CPU.
*/
for (size_t i = 0; i < MAX(len, CPUID_LEN); i++) {
uint8_t tmp, j, k;
j = i % len;
k = i % CPUID_LEN;
/* xor with CPU ID */
out[j] ^= cid[k];
/* get 'random' position */
sum += out[j];
k = sum % (j + 1);
/* shuffle bytes */
tmp = out[j];
out[j] = out[k];
out[k] = tmp;
}
_luid_round(cid, sizeof(cid), buf, len);
_luid_round(buf, len, buf, len);
#endif
}