From 31de761c6bdce0878debe7c8d5240f6a7a4315df Mon Sep 17 00:00:00 2001 From: tholo Date: Sat, 30 Mar 1996 10:01:47 +0000 Subject: [PATCH] Substantially improve random number generation by using the largest prime that fits inside 32 bits as the denominator; take care not to overflow. Regenerate initial seed after replacing the generator --- lib/libc/stdlib/random.c | 30 +++++++++++++++++++++--------- 1 file changed, 21 insertions(+), 9 deletions(-) diff --git a/lib/libc/stdlib/random.c b/lib/libc/stdlib/random.c index 469b6d976a2..9b1fe3c7381 100644 --- a/lib/libc/stdlib/random.c +++ b/lib/libc/stdlib/random.c @@ -33,7 +33,7 @@ #if defined(LIBC_SCCS) && !defined(lint) /*static char *sccsid = "from: @(#)random.c 5.9 (Berkeley) 2/23/91";*/ -static char *rcsid = "$Id: random.c,v 1.1.1.1 1995/10/18 08:42:19 deraadt Exp $"; +static char *rcsid = "$Id: random.c,v 1.2 1996/03/30 10:01:47 tholo Exp $"; #endif /* LIBC_SCCS and not lint */ #include @@ -136,12 +136,12 @@ static int seps [MAX_TYPES] = { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 }; static long randtbl[DEG_3 + 1] = { TYPE_3, - 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, + 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, }; /* @@ -193,15 +193,27 @@ void srandom(x) u_int x; { + register long int test; register int i, j; + ldiv_t val; if (rand_type == TYPE_0) state[0] = x; else { j = 1; state[0] = x; - for (i = 1; i < rand_deg; i++) - state[i] = 1103515245 * state[i - 1] + 12345; + for (i = 1; i < rand_deg; i++) { + /* + * Implement the following, without overflowing 31 bits: + * + * state[i] = (16807 * state[i - 1]) % 2147483647; + * + * 2^31-1 (prime) = 2147483647 = 127773*16807+2836 + */ + val = ldiv(state[i-1], 127773); + test = 16807 * val.rem - 2836 * val.quot; + state[i] = test + (test < 0 ? 2147483647 : 0); + } fptr = &state[rand_sep]; rptr = &state[0]; for (i = 0; i < 10 * rand_deg; i++) -- 2.20.1