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/*
* 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 <inttypes.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, 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);
}
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