/* $NetBSD: lfsr.c,v 1.1.2.2 2024/02/24 13:07:20 martin Exp $ */ /* * Copyright (C) Internet Systems Consortium, Inc. ("ISC") * * SPDX-License-Identifier: MPL-2.0 * * This Source Code Form is subject to the terms of the Mozilla Public * License, v. 2.0. If a copy of the MPL was not distributed with this * file, you can obtain one at https://mozilla.org/MPL/2.0/. * * See the COPYRIGHT file distributed with this work for additional * information regarding copyright ownership. */ /*! \file */ #include #include #include #include #include #include #define VALID_LFSR(x) (x != NULL) void isc_lfsr_init(isc_lfsr_t *lfsr, uint32_t state, unsigned int bits, 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 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 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. */ uint32_t isc_lfsr_generate32(isc_lfsr_t *lfsr1, isc_lfsr_t *lfsr2) { uint32_t state1, state2; 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); }