1 /*
2 * Copyright (C) 2004, 2005, 2007 Internet Systems Consortium, Inc. ("ISC")
3 * Copyright (C) 1999-2002 Internet Software Consortium.
4 *
5 * Permission to use, copy, modify, and/or distribute this software for any
6 * purpose with or without fee is hereby granted, provided that the above
7 * copyright notice and this permission notice appear in all copies.
8 *
9 * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
10 * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
11 * AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
12 * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
13 * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
14 * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
15 * PERFORMANCE OF THIS SOFTWARE.
16 */
17
18 /* $Id: lfsr.c,v 1.20 2007/06/19 23:47:17 tbox Exp $ */
19
20 /*! \file */
21
22 #include <config.h>
23
24 #include <stddef.h>
25 #include <stdlib.h>
26
27 #include <isc/assertions.h>
28 #include <isc/lfsr.h>
29 #include <isc/util.h>
30
31 #define VALID_LFSR(x) (x != NULL)
32
33 void
isc_lfsr_init(isc_lfsr_t * lfsr,isc_uint32_t state,unsigned int bits,isc_uint32_t tap,unsigned int count,isc_lfsrreseed_t reseed,void * arg)34 isc_lfsr_init(isc_lfsr_t *lfsr, isc_uint32_t state, unsigned int bits,
35 isc_uint32_t tap, unsigned int count,
36 isc_lfsrreseed_t reseed, void *arg)
37 {
38 REQUIRE(VALID_LFSR(lfsr));
39 REQUIRE(8 <= bits && bits <= 32);
40 REQUIRE(tap != 0);
41
42 lfsr->state = state;
43 lfsr->bits = bits;
44 lfsr->tap = tap;
45 lfsr->count = count;
46 lfsr->reseed = reseed;
47 lfsr->arg = arg;
48
49 if (count == 0 && reseed != NULL)
50 reseed(lfsr, arg);
51 if (lfsr->state == 0)
52 lfsr->state = 0xffffffffU >> (32 - lfsr->bits);
53 }
54
55 /*!
56 * Return the next state of the lfsr.
57 */
58 static inline isc_uint32_t
lfsr_generate(isc_lfsr_t * lfsr)59 lfsr_generate(isc_lfsr_t *lfsr)
60 {
61
62 /*
63 * If the previous state is zero, we must fill it with something
64 * here, or we will begin to generate an extremely predictable output.
65 *
66 * First, give the reseed function a crack at it. If the state is
67 * still 0, set it to all ones.
68 */
69 if (lfsr->state == 0) {
70 if (lfsr->reseed != NULL)
71 lfsr->reseed(lfsr, lfsr->arg);
72 if (lfsr->state == 0)
73 lfsr->state = 0xffffffffU >> (32 - lfsr->bits);
74 }
75
76 if (lfsr->state & 0x01) {
77 lfsr->state = (lfsr->state >> 1) ^ lfsr->tap;
78 return (1);
79 } else {
80 lfsr->state >>= 1;
81 return (0);
82 }
83 }
84
85 void
isc_lfsr_generate(isc_lfsr_t * lfsr,void * data,unsigned int count)86 isc_lfsr_generate(isc_lfsr_t *lfsr, void *data, unsigned int count)
87 {
88 unsigned char *p;
89 unsigned int bit;
90 unsigned int byte;
91
92 REQUIRE(VALID_LFSR(lfsr));
93 REQUIRE(data != NULL);
94 REQUIRE(count > 0);
95
96 p = data;
97 byte = count;
98
99 while (byte--) {
100 *p = 0;
101 for (bit = 0; bit < 7; bit++) {
102 *p |= lfsr_generate(lfsr);
103 *p <<= 1;
104 }
105 *p |= lfsr_generate(lfsr);
106 p++;
107 }
108
109 if (lfsr->count != 0 && lfsr->reseed != NULL) {
110 if (lfsr->count <= count * 8)
111 lfsr->reseed(lfsr, lfsr->arg);
112 else
113 lfsr->count -= (count * 8);
114 }
115 }
116
117 static inline isc_uint32_t
lfsr_skipgenerate(isc_lfsr_t * lfsr,unsigned int skip)118 lfsr_skipgenerate(isc_lfsr_t *lfsr, unsigned int skip)
119 {
120 while (skip--)
121 (void)lfsr_generate(lfsr);
122
123 (void)lfsr_generate(lfsr);
124
125 return (lfsr->state);
126 }
127
128 /*
129 * Skip "skip" states in "lfsr".
130 */
131 void
isc_lfsr_skip(isc_lfsr_t * lfsr,unsigned int skip)132 isc_lfsr_skip(isc_lfsr_t *lfsr, unsigned int skip)
133 {
134 REQUIRE(VALID_LFSR(lfsr));
135
136 while (skip--)
137 (void)lfsr_generate(lfsr);
138 }
139
140 /*
141 * Skip states in lfsr1 and lfsr2 using the other's current state.
142 * Return the final state of lfsr1 ^ lfsr2.
143 */
144 isc_uint32_t
isc_lfsr_generate32(isc_lfsr_t * lfsr1,isc_lfsr_t * lfsr2)145 isc_lfsr_generate32(isc_lfsr_t *lfsr1, isc_lfsr_t *lfsr2)
146 {
147 isc_uint32_t state1, state2;
148 isc_uint32_t skip1, skip2;
149
150 REQUIRE(VALID_LFSR(lfsr1));
151 REQUIRE(VALID_LFSR(lfsr2));
152
153 skip1 = lfsr1->state & 0x01;
154 skip2 = lfsr2->state & 0x01;
155
156 /* cross-skip. */
157 state1 = lfsr_skipgenerate(lfsr1, skip2);
158 state2 = lfsr_skipgenerate(lfsr2, skip1);
159
160 return (state1 ^ state2);
161 }
162