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1) Unifdef USE_WEAK_SEEDING it is too obsolete to support and makes reading

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harder.

2) ACM paper require seed to be in [1, 2^31-2] range, so use the same range
shifting as already done for rand(3). Also protect srandomdev() + TYPE_0 case
(non default) from negative seeds.

3) Don't check for valid "type" range in setstate(), it is always valid as
calculated. Instead add a check that rear pointer not exceeed end pointer.

MFC after:      1 week
This commit is contained in:
ache 2016-05-29 11:54:09 +00:00
parent c2282cdf4e
commit bfed8b7764
1 changed files with 14 additions and 46 deletions
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60
lib/libc/stdlib/random.c
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@ -137,11 +137,7 @@ __FBSDID("$FreeBSD$");
*/
#define MAX_TYPES 5 /* max number of types above */
#ifdef USE_WEAK_SEEDING
#define NSHUFF 0
#else /* !USE_WEAK_SEEDING */
#define NSHUFF 50 /* to drop some "seed -> 1st value" linearity */
#endif /* !USE_WEAK_SEEDING */
static const int degrees[MAX_TYPES] = { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 };
static const int seps [MAX_TYPES] = { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 };
@ -162,23 +158,12 @@ static const int seps [MAX_TYPES] = { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 };
static uint32_t randtbl[DEG_3 + 1] = {
TYPE_3,
#ifdef USE_WEAK_SEEDING
/* Historic implementation compatibility */
/* The random sequences do not vary much with the seed */
0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342, 0xde3b81e0, 0xdf0a6fb5,
0xf103bc02, 0x48f340fb, 0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd,
0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86, 0xda672e2a, 0x1588ca88,
0xe369735d, 0x904f35f7, 0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc,
0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b, 0xf5ad9d0e, 0x8999220b,
0x27fb47b9,
#else /* !USE_WEAK_SEEDING */
0x991539b1, 0x16a5bce3, 0x6774a4cd, 0x3e01511e, 0x4e508aaa, 0x61048c05,
0xf5500617, 0x846b7115, 0x6a19892c, 0x896a97af, 0xdb48f936, 0x14898454,
0x37ffd106, 0xb58bff9c, 0x59e17104, 0xcf918a49, 0x09378c83, 0x52c7a471,
0x8d293ea9, 0x1f4fc301, 0xc3db71be, 0x39b44e1c, 0xf8a44ef9, 0x4c8b80b1,
0x19edc328, 0x87bf4bdd, 0xc9b240e5, 0xe9ee4b1b, 0x4382aee7, 0x535b6b41,
0xf3bec5da
#endif /* !USE_WEAK_SEEDING */
0x2cf41758, 0x27bb3711, 0x4916d4d1, 0x7b02f59f, 0x9b8e28eb, 0xc0e80269,
0x696f5c16, 0x878f1ff5, 0x52d9c07f, 0x916a06cd, 0xb50b3a20, 0x2776970a,
0xee4eb2a6, 0xe94640ec, 0xb1d65612, 0x9d1ed968, 0x1043f6b7, 0xa3432a76,
0x17eacbb9, 0x3c09e2eb, 0x4f8c2b3, 0x708a1f57, 0xee341814, 0x95d0e4d2,
0xb06f216c, 0x8bd2e72e, 0x8f7c38d7, 0xcfc6a8fc, 0x2a59495, 0xa20d2a69,
0xe29d12d1
};
/*
@ -215,16 +200,8 @@ static int rand_sep = SEP_3;
static uint32_t *end_ptr = &randtbl[DEG_3 + 1];
static inline uint32_t
good_rand(int32_t x)
good_rand(uint32_t ctx)
{
#ifdef USE_WEAK_SEEDING
/*
* Historic implementation compatibility.
* The random sequences do not vary much with the seed,
* even with overflowing.
*/
return (1103515245 * x + 12345);
#else /* !USE_WEAK_SEEDING */
/*
* Compute x = (7^5 * x) mod (2^31 - 1)
* wihout overflowing 31 bits:
@ -233,18 +210,17 @@ good_rand(int32_t x)
* Park and Miller, Communications of the ACM, vol. 31, no. 10,
* October 1988, p. 1195.
*/
int32_t hi, lo;
int32_t hi, lo, x;
/* Can't be initialized with 0, so use another value. */
if (x == 0)
x = 123459876;
/* Transform to [1, 0x7ffffffe] range. */
x = (ctx % 0x7ffffffe) + 1;
hi = x / 127773;
lo = x % 127773;
x = 16807 * lo - 2836 * hi;
if (x < 0)
x += 0x7fffffff;
return (x);
#endif /* !USE_WEAK_SEEDING */
/* Transform to [0, 0x7ffffffd] range. */
return (x - 1);
}
/*
@ -404,16 +380,8 @@ setstate(char *arg_state)
uint32_t rear = new_state[0] / MAX_TYPES;
char *ostate = (char *)(&state[-1]);
switch(type) {
case TYPE_0:
case TYPE_1:
case TYPE_2:
case TYPE_3:
case TYPE_4:
break;
default:
if (type != TYPE_0 && rear >= degrees[type])
return (NULL);
}
if (rand_type == TYPE_0)
state[-1] = rand_type;
else
@ -455,7 +423,7 @@ random(void)
if (rand_type == TYPE_0) {
i = state[0];
state[0] = i = (good_rand(i)) & 0x7fffffff;
state[0] = i = good_rand(i);
} else {
/*
* Use local variables rather than static variables for speed.