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ntp 4.2.6p5

    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 1.1.1.1 2012/05/29 12:08:38 misho 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
   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
   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
   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
  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
  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
  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: }