lib/isc/bitstring.c

	bitstring.c revision 1819606910e5216e4adba6e0d32fd6e62dec3c97
/*
 * Copyright (C) 1999  Internet Software Consortium.
 *
 * Permission to use, copy, modify, and 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 INTERNET SOFTWARE CONSORTIUM DISCLAIMS
 * ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
 * CONSORTIUM 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.
 */

#include <config.h>

#include <stddef.h>

#include <isc/types.h>
#include <isc/assertions.h>
#include <isc/bitstring.h>

#define DIV8(x)			((x) >> 3)
#define MOD8(x)			((x) & 0x00000007U)
#define OCTETS(n)		((n + 7) >> 3)
#define PADDED(n)		(((n + 7) >> 3) << 3)
#define BITSET(bs, n) 		(((bs)->data[DIV8(n)] & \
				 (1 << (7 - MOD8(n)))) != 0)
#define SETBIT(bs, n)		(bs)->data[DIV8(n)] |= (1 << (7 - MOD8(n)))
#define CLEARBIT(bs, n)		(bs)->data[DIV8(n)] &= ~(1 << (7 - MOD8(n)))

#define BITSTRING_MAGIC			0x42537472U	/* BStr. */
#define VALID_BITSTRING(b)		((b) != NULL && \
					 (b)->magic == BITSTRING_MAGIC)

void
isc_bitstring_init(isc_bitstring_t *bitstring, unsigned char *data,
		   unsigned int length, unsigned int size, isc_boolean_t lsb0)
{
	/*
	 * Make 'bitstring' refer to the bitstring of 'size' bits starting
	 * at 'data'.  'length' bits of the bitstring are valid.  If 'lsb0'
	 * is set then, bit 0 refers to the least significant bit of the
	 * bitstring.  Otherwise bit 0 is the most significant bit.
	 */

	REQUIRE(bitstring != NULL);
	REQUIRE(data != NULL);
	REQUIRE(length <= size);

	bitstring->magic = BITSTRING_MAGIC;
	bitstring->data = data;
	bitstring->length = length;
	bitstring->size = size;
	bitstring->lsb0 = lsb0;
}

void
isc_bitstring_invalidate(isc_bitstring_t *bitstring) {

	/*
	 * Invalidate 'bitstring'.
	 */

	REQUIRE(VALID_BITSTRING(bitstring));

	bitstring->magic = 0;
	bitstring->data = NULL;
	bitstring->length = 0;
	bitstring->size = 0;
	bitstring->lsb0 = ISC_FALSE;
}

void
isc_bitstring_copy(isc_bitstring_t *source, unsigned int sbitpos,
		   isc_bitstring_t *target, unsigned int tbitpos,
		   unsigned int n)
{
	unsigned int tlast;

	/*
	 * Starting at bit 'sbitpos', copy 'n' bits from 'source' to
	 * the 'n' bits of 'target' starting at 'tbitpos'.
	 */

	REQUIRE(VALID_BITSTRING(source));
	REQUIRE(VALID_BITSTRING(target));
	if (source->lsb0) {
		REQUIRE(sbitpos < source->length);
		sbitpos = PADDED(source->size) - sbitpos - 1;
		REQUIRE(sbitpos >= n - 1);
		sbitpos -= n - 1;
	} else
		REQUIRE(sbitpos + n <= source->length);
	tlast = tbitpos + n;
	if (target->lsb0) {
		REQUIRE(tbitpos <= target->length);
		tbitpos = PADDED(target->size) - tbitpos - 1;
		REQUIRE(tbitpos >= n - 1);
		tbitpos -= n - 1;
	} else
		REQUIRE(tlast<= target->size);

	if (tlast > target->length)
		target->length = tlast;

	/*
	 * This is far from optimal...
	 */

	while (n > 0) {
		if (BITSET(source, sbitpos))
			SETBIT(target, tbitpos);
		else
			CLEARBIT(target, tbitpos);
		sbitpos++;
		tbitpos++;
		n--;
	}
}