src/bitvec.c

/* (C) 2009 by Harald Welte <laforge@gnumonks.org>
 * (C) 2012 Ivan Klyuchnikov
 * (C) 2015 by sysmocom - s.f.m.c. GmbH
 *
 * All Rights Reserved
 *
 * SPDX-License-Identifier: GPL-2.0+
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 */

/*! \addtogroup bitvec
 *  @{
 *  Osmocom bit vector abstraction utility routines.
 *
 *  These functions assume a MSB (most significant bit) first layout of the
 *  bits, so that for instance the 5 bit number abcde (a is MSB) can be
 *  embedded into a byte sequence like in xxxxxxab cdexxxxx. The bit count
 *  starts with the MSB, so the bits in a byte are numbered (MSB) 01234567 (LSB).
 *  Note that there are other incompatible encodings, like it is used
 *  for the EGPRS RLC data block headers (there the bits are numbered from LSB
 *  to MSB).
 *
 * \file bitvec.c */

#include <errno.h>
#include <stdint.h>
#include <string.h>
#include <stdio.h>
#include <stdbool.h>

#include <osmocom/core/bits.h>
#include <osmocom/core/bitvec.h>
#include <osmocom/core/panic.h>
#include <osmocom/core/utils.h>

#define BITNUM_FROM_COMP(byte, bit)	((byte*8)+bit)

static inline unsigned int bytenum_from_bitnum(unsigned int bitnum)
{
	unsigned int bytenum = bitnum / 8;

	return bytenum;
}

/* convert ZERO/ONE/L/H to a bitmask at given pos in a byte */
static uint8_t bitval2mask(enum bit_value bit, uint8_t bitnum)
{
	switch (bit) {
	case ZERO:
		return (0 << bitnum);
	case ONE:
		return (1 << bitnum);
	case L:
		return ((0x2b ^ (0 << bitnum)) & (1 << bitnum));
	case H:
		return ((0x2b ^ (1 << bitnum)) & (1 << bitnum));
	default:
		return 0;
	}
}

/*! check if the bit is 0 or 1 for a given position inside a bitvec
 *  \param[in] bv the bit vector on which to check
 *  \param[in] bitnr the bit number inside the bit vector to check
 *  \return value of the requested bit
 */
enum bit_value bitvec_get_bit_pos(const struct bitvec *bv, unsigned int bitnr)
{
	unsigned int bytenum = bytenum_from_bitnum(bitnr);
	unsigned int bitnum = 7 - (bitnr % 8);
	uint8_t bitval;

	if (bytenum >= bv->data_len)
		return -EINVAL;

	bitval = bitval2mask(ONE, bitnum);

	if (bv->data[bytenum] & bitval)
		return ONE;

	return ZERO;
}

/*! check if the bit is L or H for a given position inside a bitvec
 *  \param[in] bv the bit vector on which to check
 *  \param[in] bitnr the bit number inside the bit vector to check
 *  \return value of the requested bit
 */
enum bit_value bitvec_get_bit_pos_high(const struct bitvec *bv,
					unsigned int bitnr)
{
	unsigned int bytenum = bytenum_from_bitnum(bitnr);
	unsigned int bitnum = 7 - (bitnr % 8);
	uint8_t bitval;

	if (bytenum >= bv->data_len)
		return -EINVAL;

	bitval = bitval2mask(H, bitnum);

	if ((bv->data[bytenum] & (1 << bitnum)) == bitval)
		return H;

	return L;
}

/*! get the Nth set bit inside the bit vector
 *  \param[in] bv the bit vector to use
 *  \param[in] n the bit number to get
 *  \returns the bit number (offset) of the Nth set bit in \a bv
 */
unsigned int bitvec_get_nth_set_bit(const struct bitvec *bv, unsigned int n)
{
	unsigned int i, k = 0;

	for (i = 0; i < bv->data_len*8; i++) {
		if (bitvec_get_bit_pos(bv, i) == ONE) {
			k++;
			if (k == n)
				return i;
		}
	}

	return 0;
}

/*! set a bit at given position in a bit vector
 *  \param[in] bv bit vector on which to operate
 *  \param[in] bitnr number of bit to be set
 *  \param[in] bit value to which the bit is to be set
 *  \returns 0 on success, negative value on error
 */
inline int bitvec_set_bit_pos(struct bitvec *bv, unsigned int bitnr,
			enum bit_value bit)
{
	unsigned int bytenum = bytenum_from_bitnum(bitnr);
	unsigned int bitnum = 7 - (bitnr % 8);
	uint8_t bitval;

	if (bytenum >= bv->data_len)
		return -EINVAL;

	/* first clear the bit */
	bitval = bitval2mask(ONE, bitnum);
	bv->data[bytenum] &= ~bitval;

	/* then set it to desired value */
	bitval = bitval2mask(bit, bitnum);
	bv->data[bytenum] |= bitval;

	return 0;
}

/*! set the next bit inside a bitvec
 *  \param[in] bv bit vector to be used
 *  \param[in] bit value of the bit to be set
 *  \returns 0 on success, negative value on error
 */
inline int bitvec_set_bit(struct bitvec *bv, enum bit_value bit)
{
	int rc;

	rc = bitvec_set_bit_pos(bv, bv->cur_bit, bit);
	if (!rc)
		bv->cur_bit++;

	return rc;
}

/*! get the next bit (low/high) inside a bitvec
 *  \return value of th next bit in the vector */
int bitvec_get_bit_high(struct bitvec *bv)
{
	int rc;

	rc = bitvec_get_bit_pos_high(bv, bv->cur_bit);
	if (rc >= 0)
		bv->cur_bit++;

	return rc;
}

/*! set multiple bits (based on array of bitvals) at current pos
 *  \param[in] bv bit vector
 *  \param[in] bits array of \ref bit_value
 *  \param[in] count number of bits to set
 *  \return 0 on success; negative in case of error */
int bitvec_set_bits(struct bitvec *bv, const enum bit_value *bits, unsigned int count)
{
	int i, rc;

	for (i = 0; i < count; i++) {
		rc = bitvec_set_bit(bv, bits[i]);
		if (rc)
			return rc;
	}

	return 0;
}

/*! set multiple bits (based on numeric value) at current pos.
 *  \param[in] bv bit vector.
 *  \param[in] v mask representing which bits needs to be set.
 *  \param[in] num_bits number of meaningful bits in the mask.
 *  \param[in] use_lh whether to interpret the bits as L/H values or as 0/1.
 *  \return 0 on success; negative in case of error. */
int bitvec_set_u64(struct bitvec *bv, uint64_t v, uint8_t num_bits, bool use_lh)
{
	uint8_t i;

	if (num_bits > 64)
		return -E2BIG;

	for (i = 0; i < num_bits; i++) {
		int rc;
		enum bit_value bit = use_lh ? L : 0;

		if (v & ((uint64_t)1 << (num_bits - i - 1)))
			bit = use_lh ? H : 1;

		rc = bitvec_set_bit(bv, bit);
		if (rc != 0)
			return rc;
	}

	return 0;
}

/*! set multiple bits (based on numeric value) at current pos.
 *  \return 0 in case of success; negative in case of error. */
int bitvec_set_uint(struct bitvec *bv, unsigned int ui, unsigned int num_bits)
{
	return bitvec_set_u64(bv, ui, num_bits, false);
}

/*! get multiple bits (num_bits) from beginning of vector (MSB side)
 *  \return 16bit signed integer retrieved from bit vector */
int16_t bitvec_get_int16_msb(const struct bitvec *bv, unsigned int num_bits)
{
	if (num_bits > 15 || bv->cur_bit < num_bits)
		return -EINVAL;

	if (num_bits < 9)
		return bv->data[0] >> (8 - num_bits);

	return osmo_load16be(bv->data) >> (16 - num_bits);
}

/*! get multiple bits (based on numeric value) from current pos
 *  \return integer value retrieved from bit vector */
int bitvec_get_uint(struct bitvec *bv, unsigned int num_bits)
{
	int i;
	unsigned int ui = 0;

	for (i = 0; i < num_bits; i++) {
		int bit = bitvec_get_bit_pos(bv, bv->cur_bit);
		if (bit < 0)
			return bit;
		if (bit)
			ui |= ((unsigned)1 << (num_bits - i - 1));
		bv->cur_bit++;
	}

	return ui;
}

/*! fill num_bits with \fill starting from the current position
 *  \return 0 on success; negative otherwise (out of vector boundary)
 */
int bitvec_fill(struct bitvec *bv, unsigned int num_bits, enum bit_value fill)
{
	unsigned i, stop = bv->cur_bit + num_bits;
	for (i = bv->cur_bit; i < stop; i++)
		if (bitvec_set_bit(bv, fill) < 0)
			return -EINVAL;

	return 0;
}

/*! pad all remaining bits up to a given bit number
 *  \return 0 on success; negative otherwise */
int bitvec_spare_padding(struct bitvec *bv, unsigned int up_to_bit)
{
	int n = up_to_bit - bv->cur_bit + 1;
	if (n < 1)
		return 0;

	return bitvec_fill(bv, n, L);
}

/*! find first bit set in bit vector
 *  \return 0 on success; negative otherwise */
int bitvec_find_bit_pos(const struct bitvec *bv, unsigned int n,
			enum bit_value val)
{
	unsigned int i;

	for (i = n; i < bv->data_len*8; i++) {
		if (bitvec_get_bit_pos(bv, i) == val)
			return i;
	}

	return -1;
}

/*! get multiple bytes from current pos
 *  Assumes MSB first encoding.
 *  \param[in] bv bit vector
 *  \param[in] bytes array
 *  \param[in] count number of bytes to copy
 *  \return 0 on success; negative otherwise
 */
int bitvec_get_bytes(struct bitvec *bv, uint8_t *bytes, unsigned int count)
{
	int byte_offs = bytenum_from_bitnum(bv->cur_bit);
	int bit_offs = bv->cur_bit % 8;
	uint8_t c, last_c;
	int i;
	uint8_t *src;

	if (byte_offs + count + (bit_offs ? 1 : 0) > bv->data_len)
		return -EINVAL;

	if (bit_offs == 0) {
		memcpy(bytes, bv->data + byte_offs, count);
	} else {
		src = bv->data + byte_offs;
		last_c = *(src++);
		for (i = count; i > 0; i--) {
			c = *(src++);
			*(bytes++) =
				(last_c << bit_offs) |
				(c >> (8 - bit_offs));
			last_c = c;
		}
	}

	bv->cur_bit += count * 8;
	return 0;
}

/*! set multiple bytes at current pos
 *  Assumes MSB first encoding.
 *  \param[in] bv bit vector
 *  \param[in] bytes array
 *  \param[in] count number of bytes to copy
 *  \return 0 on success; negative otherwise
 */
int bitvec_set_bytes(struct bitvec *bv, const uint8_t *bytes, unsigned int count)
{
	int byte_offs = bytenum_from_bitnum(bv->cur_bit);
	int bit_offs = bv->cur_bit % 8;
	uint8_t c, last_c;
	int i;
	uint8_t *dst;

	if (byte_offs + count + (bit_offs ? 1 : 0) > bv->data_len)
		return -EINVAL;

	if (bit_offs == 0) {
		memcpy(bv->data + byte_offs, bytes, count);
	} else if (count > 0) {
		dst = bv->data + byte_offs;
		/* Get lower bits of first dst byte */
		last_c = *dst >> (8 - bit_offs);
		for (i = count; i > 0; i--) {
			c = *(bytes++);
			*(dst++) =
				(last_c << (8 - bit_offs)) |
				(c >> bit_offs);
			last_c = c;
		}
		/* Overwrite lower bits of N+1 dst byte */
		*dst = (*dst & ((1 << (8 - bit_offs)) - 1)) |
			(last_c << (8 - bit_offs));
	}

	bv->cur_bit += count * 8;
	return 0;
}

/*! Allocate a bit vector
 *  \param[in] size Number of bytes in the vector
 *  \param[in] ctx Context from which to allocate
 *  \return pointer to allocated vector; NULL in case of error */
struct bitvec *bitvec_alloc(unsigned int size, TALLOC_CTX *ctx)
{
	struct bitvec *bv = talloc(ctx, struct bitvec);
	if (!bv)
		return NULL;

	bv->data = talloc_zero_array(bv, uint8_t, size);
	if (!(bv->data)) {
		talloc_free(bv);
		return NULL;
	}

	bv->data_len = size;
	bv->cur_bit = 0;
	return bv;
}

/*! Free a bit vector (release its memory)
 *  \param[in] bit vector to free */
void bitvec_free(struct bitvec *bv)
{
	if (bv == NULL)
		return;
	talloc_free(bv->data);
	talloc_free(bv);
}

/*! Export a bit vector to a buffer
 *  \param[in] bitvec (unpacked bits)
 *  \param[out] buffer for the unpacked bits
 *  \return number of bytes (= bits) copied */
unsigned int bitvec_pack(const struct bitvec *bv, uint8_t *buffer)
{
	unsigned int i;
	for (i = 0; i < bv->data_len; i++)
		buffer[i] = bv->data[i];

	return i;
}

/*! Copy buffer of unpacked bits into bit vector
 *  \param[in] buffer unpacked input bits
 *  \param[out] bv unpacked bit vector
 *  \return number of bytes (= bits) copied */
unsigned int bitvec_unpack(struct bitvec *bv, const uint8_t *buffer)
{
	unsigned int i;
	for (i = 0; i < bv->data_len; i++)
		bv->data[i] = buffer[i];

	return i;
}

/*! read hexadecimap string into a bit vector
 *  \param[in] src string containing hex digits
 *  \param[out] bv unpacked bit vector
 *  \return 0 in case of success; 1 in case of error
 */
int bitvec_unhex(struct bitvec *bv, const char *src)
{
	int rc;

	rc = osmo_hexparse(src, bv->data, bv->data_len);
	if (rc < 0) /* turn -1 into 1 in case of error */
		return 1;

	bv->cur_bit = rc * 8;
	return 0;
}

/*! read part of the vector
 *  \param[in] bv The boolean vector to work on
 *  \param[in,out] read_index Where reading supposed to start in the vector
 *  \param[in] len How many bits to read from vector
 *  \returns An integer made up of the bits read.
 *
 * In case of an error, errno is set to a non-zero value.  Otherwise it holds 0.
 */
uint64_t bitvec_read_field(struct bitvec *bv, unsigned int *read_index, unsigned int len)
{
	unsigned int i;
	uint64_t ui = 0;

	/* Prevent bitvec overrun due to incorrect index and/or length */
	if (len && bytenum_from_bitnum(*read_index + len - 1) >= bv->data_len) {
		errno = EOVERFLOW;
		return 0;
	}

	bv->cur_bit = *read_index;
	errno = 0;

	for (i = 0; i < len; i++) {
		unsigned int bytenum = bytenum_from_bitnum(bv->cur_bit);
		unsigned int bitnum = 7 - (bv->cur_bit % 8);

		if (bv->data[bytenum] & (1 << bitnum))
			ui |= ((uint64_t)1 << (len - i - 1));
		bv->cur_bit++;
	}
	*read_index += len;
	return ui;
}

/*! write into the vector
 *  \param[in] bv The boolean vector to work on
 *  \param[in,out] write_index Where writing supposed to start in the vector
 *  \param[in] len How many bits to write
 *  \returns 0 on success, negative value on error
 */
int bitvec_write_field(struct bitvec *bv, unsigned int *write_index, uint64_t val, unsigned int len)
{
	int rc;

	bv->cur_bit = *write_index;

	rc = bitvec_set_u64(bv, val, len, false);
	if (rc != 0)
		return rc;

	*write_index += len;

	return 0;
}

/*! convert enum to corresponding character
 *  \param v input value (bit)
 *  \return single character, either 0, 1, L or H */
char bit_value_to_char(enum bit_value v)
{
	switch (v) {
	case ZERO: return '0';
	case ONE: return '1';
	case L: return 'L';
	case H: return 'H';
	default: osmo_panic("unexpected input in bit_value_to_char"); return 'X';
	}
}

/*! prints bit vector to provided string
 * It's caller's responsibility to ensure that we won't shoot him in the foot:
 * the provided buffer should be at lest cur_bit + 1 bytes long
 */
void bitvec_to_string_r(const struct bitvec *bv, char *str)
{
	unsigned i, pos = 0;
	char *cur = str;
	for (i = 0; i < bv->cur_bit; i++) {
		if (0 == i % 8)
			*cur++ = ' ';
		*cur++ = bit_value_to_char(bitvec_get_bit_pos(bv, i));
		pos++;
	}
	*cur = 0;
}

/* we assume that x have at least 1 non-b bit */
static inline unsigned leading_bits(uint8_t x, bool b)
{
	if (b) {
		if (x < 0x80) return 0;
		if (x < 0xC0) return 1;
		if (x < 0xE0) return 2;
		if (x < 0xF0) return 3;
		if (x < 0xF8) return 4;
		if (x < 0xFC) return 5;
		if (x < 0xFE) return 6;
	} else {
		if (x > 0x7F) return 0;
		if (x > 0x3F) return 1;
		if (x > 0x1F) return 2;
		if (x > 0xF) return 3;
		if (x > 7) return 4;
		if (x > 3) return 5;
		if (x > 1) return 6;
	}
	return 7;
}
/*! force bit vector to all 0 and current bit to the beginnig of the vector */
void bitvec_zero(struct bitvec *bv)
{
	bv->cur_bit = 0;
	memset(bv->data, 0, bv->data_len);
}

/*! Return number (bits) of uninterrupted bit run in vector starting from the MSB
 *  \param[in] bv The boolean vector to work on
 *  \param[in] b The boolean, sequence of which is looked at from the vector start
 *  \returns Number of consecutive bits of \p b in \p bv
 */
unsigned bitvec_rl(const struct bitvec *bv, bool b)
{
	unsigned i;
	for (i = 0; i < (bv->cur_bit % 8 ? bv->cur_bit / 8 + 1 : bv->cur_bit / 8); i++) {
		if ( (b ? 0xFF : 0) != bv->data[i])
			return i * 8 + leading_bits(bv->data[i], b);
	}

	return bv->cur_bit;
}

/*! Return number (bits) of uninterrupted bit run in vector
 *   starting from the current bit
 *  \param[in] bv The boolean vector to work on
 *  \param[in] b The boolean, sequence of 1's or 0's to be checked
 *  \param[in] max_bits Total Number of Uncmopresed bits
 *  \returns Number of consecutive bits of \p b in \p bv and cur_bit will
 *  \go to cur_bit + number of consecutive bit
 */
unsigned bitvec_rl_curbit(struct bitvec *bv, bool b, int max_bits)
{
	unsigned i = 0;
	unsigned j = 8;
	int temp_res = 0;
	int count = 0;
	unsigned readIndex = bv->cur_bit;
	unsigned remaining_bits = max_bits % 8;
	unsigned remaining_bytes = max_bits / 8;
	unsigned byte_mask = 0xFF;

	if (readIndex % 8) {
		for (j -= (readIndex % 8) ; j > 0 ; j--) {
			if (readIndex < max_bits && bitvec_read_field(bv, &readIndex, 1) == b)
				temp_res++;
			else {
				bv->cur_bit--;
				return temp_res;
			}
		}
	}
	for (i = (readIndex / 8);
			i < (remaining_bits ? remaining_bytes + 1 : remaining_bytes);
			i++, count++) {
		if ((b ? byte_mask : 0) != bv->data[i]) {
			bv->cur_bit = (count * 8 +
					leading_bits(bv->data[i], b) + readIndex);
			return count * 8 +
				leading_bits(bv->data[i], b) + temp_res;
		}
	}
	bv->cur_bit = (temp_res + (count * 8)) + readIndex;
	if (bv->cur_bit > max_bits)
		bv->cur_bit = max_bits;
	return (bv->cur_bit - readIndex + temp_res);
}

/*! Shifts bitvec to the left, n MSB bits lost */
void bitvec_shiftl(struct bitvec *bv, unsigned n)
{
	if (0 == n)
		return;
	if (n >= bv->cur_bit) {
		bitvec_zero(bv);
		return;
	}

	memmove(bv->data, bv->data + n / 8, bv->data_len - n / 8);

	uint8_t tmp[2];
	unsigned i;
	for (i = 0; i < bv->data_len - 2; i++) {
		uint16_t t = osmo_load16be(bv->data + i);
		osmo_store16be(t << (n % 8), &tmp);
		bv->data[i] = tmp[0];
	}

	bv->data[bv->data_len - 1] <<= (n % 8);
	bv->cur_bit -= n;
}

/*! Add given array to bitvec
 *  \param[in,out] bv bit vector to work with
 *  \param[in] array elements to be added
 *  \param[in] array_len length of array
 *  \param[in] dry_run indicates whether to return number of bits required
 *  instead of adding anything to bv for real
 *  \param[in] num_bits number of bits to consider in each element of array
 *  \returns number of bits necessary to add array elements if dry_run is true,
 *  0 otherwise (only in this case bv is actually changed)
 *
 * N. B: no length checks are performed on bv - it's caller's job to ensure
 * enough space is available - for example by calling with dry_run = true first.
 *
 * Useful for common pattern in CSN.1 spec which looks like:
 * { 1 < XXX : bit (num_bits) > } ** 0
 * which means repeat any times (between 0 and infinity),
 * start each repetition with 1, mark end of repetitions with 0 bit
 * see app. note in 3GPP TS 24.007 § B.2.1 Rule A2
 */
unsigned int bitvec_add_array(struct bitvec *bv, const uint32_t *array,
			      unsigned int array_len, bool dry_run,
			      unsigned int num_bits)
{
	unsigned i, bits = 1; /* account for stop bit */
	for (i = 0; i < array_len; i++) {
		if (dry_run) {
			bits += (1 + num_bits);
		} else {
			bitvec_set_bit(bv, 1);
			bitvec_set_uint(bv, array[i], num_bits);
		}
	}

	if (dry_run)
		return bits;

	bitvec_set_bit(bv, 0); /* stop bit - end of the sequence */
	return 0;
}

/*! @} */