Improve seeding, the random sequence did not vary match
with the seed. Old variant will be available via libcompat soon.
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@ -82,15 +82,8 @@ are usable. For example,
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will produce a random binary
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value.
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.Pp
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Unlike
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.Xr srand ,
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.Fn srandom
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does not return the old seed; the reason for this is that the amount of
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state information used is much more than a single word. (Two other
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routines are provided to deal with restarting/changing random
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number generators). Like
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Like
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.Xr rand 3 ,
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however,
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.Fn random
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will by default produce a sequence of numbers that can be duplicated
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by calling
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@ -161,11 +154,29 @@ is called with less than 8 bytes of state information, or if
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detects that the state information has been garbled, error
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messages are printed on the standard error output.
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.Sh SEE ALSO
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.Xr rand 3
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.Xr rand 3 ,
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.Xr srand 3
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.Sh HISTORY
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These
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functions appeared in
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.Bx 4.2 .
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.Sh BUGS
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.Pp
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About 2/3 the speed of
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.Xr rand 3 .
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.Pp
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The historical implementation used to have a very weak seeding; the
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random sequence did not vary much with the seed. For compatibility
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reasons, this implementation has been made available until the
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next FreeBSD release
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via the
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functions
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.Fn orandom ,
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.Fn osrandom ,
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.Fn oinitstate
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and
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.Fn osetstate
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from the compatibility library,
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.Em libcompat .
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The current implementation employs a better pseudo-random number
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generator for the initial state calculation.
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@ -35,6 +35,14 @@
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static char sccsid[] = "@(#)random.c 8.1 (Berkeley) 6/4/93";
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#endif /* LIBC_SCCS and not lint */
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#ifdef COMPAT_WEAK_SEEDING
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#define USE_WEAK_SEEDING
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#define random orandom
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#define srandom osrandom
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#define initstate oinitstate
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#define setstate osetstate
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#endif
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#include <stdio.h>
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#include <stdlib.h>
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@ -122,7 +130,7 @@ static int seps [MAX_TYPES] = { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 };
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/*
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* Initially, everything is set up as if from:
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*
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* initstate(1, &randtbl, 128);
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* initstate(1, randtbl, 128);
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*
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* Note that this initialization takes advantage of the fact that srandom()
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* advances the front and rear pointers 10*rand_deg times, and hence the
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@ -135,12 +143,23 @@ static int seps [MAX_TYPES] = { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 };
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static long randtbl[DEG_3 + 1] = {
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TYPE_3,
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#ifdef USE_WEAK_SEEDING
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/* Historic implementation compatibility */
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/* The random sequences do not vary much with the seed */
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0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342, 0xde3b81e0, 0xdf0a6fb5,
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0xf103bc02, 0x48f340fb, 0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd,
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0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86, 0xda672e2a, 0x1588ca88,
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0xe369735d, 0x904f35f7, 0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc,
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0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b, 0xf5ad9d0e, 0x8999220b,
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0x27fb47b9,
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#else /* !USE_WEAK_SEEDING */
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0x991539b1, 0x16a5bce3, 0x6774a4cd, 0x3e01511e, 0x4e508aaa, 0x61048c05,
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0xf5500617, 0x846b7115, 0x6a19892c, 0x896a97af, 0xdb48f936, 0x14898454,
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0x37ffd106, 0xb58bff9c, 0x59e17104, 0xcf918a49, 0x09378c83, 0x52c7a471,
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0x8d293ea9, 0x1f4fc301, 0xc3db71be, 0x39b44e1c, 0xf8a44ef9, 0x4c8b80b1,
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0x19edc328, 0x87bf4bdd, 0xc9b240e5, 0xe9ee4b1b, 0x4382aee7, 0x535b6b41,
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0xf3bec5da
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#endif /* !USE_WEAK_SEEDING */
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};
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/*
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@ -176,6 +195,38 @@ static int rand_deg = DEG_3;
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static int rand_sep = SEP_3;
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static long *end_ptr = &randtbl[DEG_3 + 1];
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static inline long good_rand __P((long));
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static inline long good_rand (x)
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register long x;
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{
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#ifdef USE_WEAK_SEEDING
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/*
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* Historic implementation compatibility.
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* The random sequences do not vary much with the seed,
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* even with overflowing.
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*/
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return (1103515245 * x + 12345);
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#else /* !USE_WEAK_SEEDING */
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/*
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* Compute x = (7^5 * x) mod (2^31 - 1)
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* wihout overflowing 31 bits:
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* (2^31 - 1) = 127773 * (7^5) + 2836
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* From "Random number generators: good ones are hard to find",
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* Park and Miller, Communications of the ACM, vol. 31, no. 10,
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* October 1988, p. 1195.
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*/
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register long hi, lo;
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hi = x / 127773;
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lo = x % 127773;
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x = 16807 * lo - 2836 * hi;
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if (x <= 0)
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x += 0x7fffffff;
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return (x);
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#endif /* !USE_WEAK_SEEDING */
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}
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/*
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* srandom:
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*
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@ -192,15 +243,14 @@ void
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srandom(x)
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unsigned int x;
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{
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register int i, j;
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register int i;
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if (rand_type == TYPE_0)
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state[0] = x;
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else {
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j = 1;
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state[0] = x;
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for (i = 1; i < rand_deg; i++)
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state[i] = 1103515245 * state[i - 1] + 12345;
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state[i] = good_rand(state[i - 1]);
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fptr = &state[rand_sep];
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rptr = &state[0];
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for (i = 0; i < 10 * rand_deg; i++)
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@ -349,7 +399,7 @@ random()
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long i;
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if (rand_type == TYPE_0)
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i = state[0] = (state[0] * 1103515245 + 12345) & 0x7fffffff;
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i = state[0] = good_rand(state[0]) & 0x7fffffff;
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else {
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*fptr += *rptr;
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i = (*fptr >> 1) & 0x7fffffff; /* chucking least random bit */
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