162 lines
3.6 KiB
C
162 lines
3.6 KiB
C
/*
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* Copyright (C) 2004, 2005, 2007 Internet Systems Consortium, Inc. ("ISC")
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* Copyright (C) 1999-2002 Internet Software Consortium.
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*
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* Permission to use, copy, modify, and/or distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
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* REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
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* AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
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* INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
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* LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
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* OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
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* PERFORMANCE OF THIS SOFTWARE.
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*/
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/* $Id: lfsr.c,v 1.20 2007/06/19 23:47:17 tbox Exp $ */
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/*! \file */
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#include <config.h>
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#include <stddef.h>
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#include <stdlib.h>
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#include <isc/assertions.h>
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#include <isc/lfsr.h>
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#include <isc/util.h>
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#define VALID_LFSR(x) (x != NULL)
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void
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isc_lfsr_init(isc_lfsr_t *lfsr, isc_uint32_t state, unsigned int bits,
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isc_uint32_t tap, unsigned int count,
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isc_lfsrreseed_t reseed, void *arg)
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{
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REQUIRE(VALID_LFSR(lfsr));
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REQUIRE(8 <= bits && bits <= 32);
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REQUIRE(tap != 0);
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lfsr->state = state;
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lfsr->bits = bits;
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lfsr->tap = tap;
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lfsr->count = count;
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lfsr->reseed = reseed;
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lfsr->arg = arg;
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if (count == 0 && reseed != NULL)
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reseed(lfsr, arg);
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if (lfsr->state == 0)
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lfsr->state = 0xffffffffU >> (32 - lfsr->bits);
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}
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/*!
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* Return the next state of the lfsr.
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*/
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static inline isc_uint32_t
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lfsr_generate(isc_lfsr_t *lfsr)
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{
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/*
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* If the previous state is zero, we must fill it with something
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* here, or we will begin to generate an extremely predictable output.
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*
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* First, give the reseed function a crack at it. If the state is
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* still 0, set it to all ones.
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*/
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if (lfsr->state == 0) {
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if (lfsr->reseed != NULL)
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lfsr->reseed(lfsr, lfsr->arg);
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if (lfsr->state == 0)
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lfsr->state = 0xffffffffU >> (32 - lfsr->bits);
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}
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if (lfsr->state & 0x01) {
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lfsr->state = (lfsr->state >> 1) ^ lfsr->tap;
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return (1);
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} else {
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lfsr->state >>= 1;
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return (0);
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}
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}
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void
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isc_lfsr_generate(isc_lfsr_t *lfsr, void *data, unsigned int count)
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{
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unsigned char *p;
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unsigned int bit;
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unsigned int byte;
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REQUIRE(VALID_LFSR(lfsr));
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REQUIRE(data != NULL);
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REQUIRE(count > 0);
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p = data;
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byte = count;
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while (byte--) {
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*p = 0;
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for (bit = 0; bit < 7; bit++) {
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*p |= lfsr_generate(lfsr);
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*p <<= 1;
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}
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*p |= lfsr_generate(lfsr);
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p++;
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}
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if (lfsr->count != 0 && lfsr->reseed != NULL) {
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if (lfsr->count <= count * 8)
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lfsr->reseed(lfsr, lfsr->arg);
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else
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lfsr->count -= (count * 8);
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}
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}
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static inline isc_uint32_t
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lfsr_skipgenerate(isc_lfsr_t *lfsr, unsigned int skip)
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{
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while (skip--)
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(void)lfsr_generate(lfsr);
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(void)lfsr_generate(lfsr);
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return (lfsr->state);
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}
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/*
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* Skip "skip" states in "lfsr".
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*/
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void
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isc_lfsr_skip(isc_lfsr_t *lfsr, unsigned int skip)
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{
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REQUIRE(VALID_LFSR(lfsr));
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while (skip--)
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(void)lfsr_generate(lfsr);
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}
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/*
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* Skip states in lfsr1 and lfsr2 using the other's current state.
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* Return the final state of lfsr1 ^ lfsr2.
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*/
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isc_uint32_t
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isc_lfsr_generate32(isc_lfsr_t *lfsr1, isc_lfsr_t *lfsr2)
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{
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isc_uint32_t state1, state2;
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isc_uint32_t skip1, skip2;
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REQUIRE(VALID_LFSR(lfsr1));
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REQUIRE(VALID_LFSR(lfsr2));
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skip1 = lfsr1->state & 0x01;
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skip2 = lfsr2->state & 0x01;
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/* cross-skip. */
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state1 = lfsr_skipgenerate(lfsr1, skip2);
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state2 = lfsr_skipgenerate(lfsr2, skip1);
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return (state1 ^ state2);
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}
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