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Diffstat (limited to 'lib/isc/lfsr.c')
| -rw-r--r-- | lib/isc/lfsr.c | 161 |
1 files changed, 161 insertions, 0 deletions
diff --git a/lib/isc/lfsr.c b/lib/isc/lfsr.c new file mode 100644 index 0000000..0b8d782 --- /dev/null +++ b/lib/isc/lfsr.c @@ -0,0 +1,161 @@ +/* + * Copyright (C) 2004, 2005, 2007 Internet Systems Consortium, Inc. ("ISC") + * Copyright (C) 1999-2002 Internet Software Consortium. + * + * Permission to use, copy, modify, and/or distribute this software for any + * purpose with or without fee is hereby granted, provided that the above + * copyright notice and this permission notice appear in all copies. + * + * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH + * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY + * AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT, + * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM + * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE + * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR + * PERFORMANCE OF THIS SOFTWARE. + */ + +/* $Id: lfsr.c,v 1.20 2007/06/19 23:47:17 tbox Exp $ */ + +/*! \file */ + +#include <config.h> + +#include <stddef.h> +#include <stdlib.h> + +#include <isc/assertions.h> +#include <isc/lfsr.h> +#include <isc/util.h> + +#define VALID_LFSR(x) (x != NULL) + +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) +{ + REQUIRE(VALID_LFSR(lfsr)); + REQUIRE(8 <= bits && bits <= 32); + REQUIRE(tap != 0); + + lfsr->state = state; + lfsr->bits = bits; + lfsr->tap = tap; + lfsr->count = count; + lfsr->reseed = reseed; + lfsr->arg = arg; + + if (count == 0 && reseed != NULL) + reseed(lfsr, arg); + if (lfsr->state == 0) + lfsr->state = 0xffffffffU >> (32 - lfsr->bits); +} + +/*! + * Return the next state of the lfsr. + */ +static inline isc_uint32_t +lfsr_generate(isc_lfsr_t *lfsr) +{ + + /* + * If the previous state is zero, we must fill it with something + * here, or we will begin to generate an extremely predictable output. + * + * First, give the reseed function a crack at it. If the state is + * still 0, set it to all ones. + */ + if (lfsr->state == 0) { + if (lfsr->reseed != NULL) + lfsr->reseed(lfsr, lfsr->arg); + if (lfsr->state == 0) + lfsr->state = 0xffffffffU >> (32 - lfsr->bits); + } + + if (lfsr->state & 0x01) { + lfsr->state = (lfsr->state >> 1) ^ lfsr->tap; + return (1); + } else { + lfsr->state >>= 1; + return (0); + } +} + +void +isc_lfsr_generate(isc_lfsr_t *lfsr, void *data, unsigned int count) +{ + unsigned char *p; + unsigned int bit; + unsigned int byte; + + REQUIRE(VALID_LFSR(lfsr)); + REQUIRE(data != NULL); + REQUIRE(count > 0); + + p = data; + byte = count; + + while (byte--) { + *p = 0; + for (bit = 0; bit < 7; bit++) { + *p |= lfsr_generate(lfsr); + *p <<= 1; + } + *p |= lfsr_generate(lfsr); + p++; + } + + if (lfsr->count != 0 && lfsr->reseed != NULL) { + if (lfsr->count <= count * 8) + lfsr->reseed(lfsr, lfsr->arg); + else + lfsr->count -= (count * 8); + } +} + +static inline isc_uint32_t +lfsr_skipgenerate(isc_lfsr_t *lfsr, unsigned int skip) +{ + while (skip--) + (void)lfsr_generate(lfsr); + + (void)lfsr_generate(lfsr); + + return (lfsr->state); +} + +/* + * Skip "skip" states in "lfsr". + */ +void +isc_lfsr_skip(isc_lfsr_t *lfsr, unsigned int skip) +{ + REQUIRE(VALID_LFSR(lfsr)); + + while (skip--) + (void)lfsr_generate(lfsr); +} + +/* + * Skip states in lfsr1 and lfsr2 using the other's current state. + * Return the final state of lfsr1 ^ lfsr2. + */ +isc_uint32_t +isc_lfsr_generate32(isc_lfsr_t *lfsr1, isc_lfsr_t *lfsr2) +{ + isc_uint32_t state1, state2; + isc_uint32_t skip1, skip2; + + REQUIRE(VALID_LFSR(lfsr1)); + REQUIRE(VALID_LFSR(lfsr2)); + + skip1 = lfsr1->state & 0x01; + skip2 = lfsr2->state & 0x01; + + /* cross-skip. */ + state1 = lfsr_skipgenerate(lfsr1, skip2); + state2 = lfsr_skipgenerate(lfsr2, skip1); + + return (state1 ^ state2); +} |