summaryrefslogtreecommitdiffstats
path: root/src/bits.c
blob: fa917b07c43ed875128aa25eb4a61cd4eecda7f6 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
/*
 * (C) 2011 by Harald Welte <laforge@gnumonks.org>
 * (C) 2011 by Sylvain Munaut <tnt@246tNt.com>
 *
 * All Rights Reserved
 *
 * 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.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 */

#include <stdint.h>

#include <osmocom/core/bits.h>

/*! \addtogroup bits
 *  @{
 *  Osmocom bit level support code.
 *
 *  This module implements the notion of different bit-fields, such as
 *  - unpacked bits (\ref ubit_t), i.e. 1 bit per byte
 *  - packed bits (\ref pbit_t), i.e. 8 bits per byte
 *  - soft bits (\ref sbit_t), 1 bit per byte from -127 to 127
 *
 * \file bits.c */

/*! convert unpacked bits to packed bits, return length in bytes
 *  \param[out] out output buffer of packed bits
 *  \param[in] in input buffer of unpacked bits
 *  \param[in] num_bits number of bits
 */
int osmo_ubit2pbit(pbit_t *out, const ubit_t *in, unsigned int num_bits)
{
	unsigned int i;
	uint8_t curbyte = 0;
	pbit_t *outptr = out;

	for (i = 0; i < num_bits; i++) {
		uint8_t bitnum = 7 - (i % 8);

		curbyte |= (in[i] << bitnum);

		if(i % 8 == 7){
			*outptr++ = curbyte;
			curbyte = 0;
		}
	}
	/* we have a non-modulo-8 bitcount */
	if (i % 8)
		*outptr++ = curbyte;

	return outptr - out;
}

/*! Shift unaligned input to octet-aligned output
 *  \param[out] out output buffer, unaligned
 *  \param[in] in input buffer, octet-aligned
 *  \param[in] num_nibbles number of nibbles
 */
void osmo_nibble_shift_right(uint8_t *out, const uint8_t *in,
			     unsigned int num_nibbles)
{
	unsigned int i, num_whole_bytes = num_nibbles / 2;
	if (!num_whole_bytes)
		return;

	/* first byte: upper nibble empty, lower nibble from src */
	out[0] = (in[0] >> 4);

	/* bytes 1.. */
	for (i = 1; i < num_whole_bytes; i++)
		out[i] = ((in[i - 1] & 0xF) << 4) | (in[i] >> 4);

	/* shift the last nibble, in case there's an odd count */
	i = num_whole_bytes;
	if (num_nibbles & 1)
		out[i] = ((in[i - 1] & 0xF) << 4) | (in[i] >> 4);
	else
		out[i] = (in[i - 1] & 0xF) << 4;
}

/*! Shift unaligned input to octet-aligned output
 *  \param[out] out output buffer, octet-aligned
 *  \param[in] in input buffer, unaligned
 *  \param[in] num_nibbles number of nibbles
 */
void osmo_nibble_shift_left_unal(uint8_t *out, const uint8_t *in,
				unsigned int num_nibbles)
{
	unsigned int i, num_whole_bytes = num_nibbles / 2;
	if (!num_whole_bytes)
		return;

	for (i = 0; i < num_whole_bytes; i++)
		out[i] = ((in[i] & 0xF) << 4) | (in[i + 1] >> 4);

	/* shift the last nibble, in case there's an odd count */
	i = num_whole_bytes;
	if (num_nibbles & 1)
		out[i] = (in[i] & 0xF) << 4;
}

/*! convert unpacked bits to soft bits
 *  \param[out] out output buffer of soft bits
 *  \param[in] in input buffer of unpacked bits
 *  \param[in] num_bits number of bits
 */
void osmo_ubit2sbit(sbit_t *out, const ubit_t *in, unsigned int num_bits)
{
	unsigned int i;
	for (i = 0; i < num_bits; i++)
		out[i] = in[i] ? -127 : 127;
}

/*! convert soft bits to unpacked bits
 *  \param[out] out output buffer of unpacked bits
 *  \param[in] in input buffer of soft bits
 *  \param[in] num_bits number of bits
 */
void osmo_sbit2ubit(ubit_t *out, const sbit_t *in, unsigned int num_bits)
{
	unsigned int i;
	for (i = 0; i < num_bits; i++)
		out[i] = in[i] < 0;
}

/*! convert packed bits to unpacked bits, return length in bytes
 *  \param[out] out output buffer of unpacked bits
 *  \param[in] in input buffer of packed bits
 *  \param[in] num_bits number of bits
 *  \return number of bytes used in \ref out
 */
int osmo_pbit2ubit(ubit_t *out, const pbit_t *in, unsigned int num_bits)
{
	unsigned int i;
	ubit_t *cur = out;
	ubit_t *limit = out + num_bits;

	for (i = 0; i < (num_bits/8)+1; i++) {
		pbit_t byte = in[i];
		*cur++ = (byte >> 7) & 1;
		if (cur >= limit)
			break;
		*cur++ = (byte >> 6) & 1;
		if (cur >= limit)
			break;
		*cur++ = (byte >> 5) & 1;
		if (cur >= limit)
			break;
		*cur++ = (byte >> 4) & 1;
		if (cur >= limit)
			break;
		*cur++ = (byte >> 3) & 1;
		if (cur >= limit)
			break;
		*cur++ = (byte >> 2) & 1;
		if (cur >= limit)
			break;
		*cur++ = (byte >> 1) & 1;
		if (cur >= limit)
			break;
		*cur++ = (byte >> 0) & 1;
		if (cur >= limit)
			break;
	}
	return cur - out;
}

/*! convert unpacked bits to packed bits (extended options)
 *  \param[out] out output buffer of packed bits
 *  \param[in] out_ofs offset into output buffer
 *  \param[in] in input buffer of unpacked bits
 *  \param[in] in_ofs offset into input buffer
 *  \param[in] num_bits number of bits
 *  \param[in] lsb_mode Encode bits in LSB orde instead of MSB
 *  \returns length in bytes (max written offset of output buffer + 1)
 */
int osmo_ubit2pbit_ext(pbit_t *out, unsigned int out_ofs,
                       const ubit_t *in, unsigned int in_ofs,
                       unsigned int num_bits, int lsb_mode)
{
	int i, op, bn;
	for (i=0; i<num_bits; i++) {
		op = out_ofs + i;
		bn = lsb_mode ? (op&7) : (7-(op&7));
		if (in[in_ofs+i])
			out[op>>3] |= 1 << bn;
		else
			out[op>>3] &= ~(1 << bn);
	}
	return ((out_ofs + num_bits - 1) >> 3) + 1;
}

/*! convert packed bits to unpacked bits (extended options)
 *  \param[out] out output buffer of unpacked bits
 *  \param[in] out_ofs offset into output buffer
 *  \param[in] in input buffer of packed bits
 *  \param[in] in_ofs offset into input buffer
 *  \param[in] num_bits number of bits
 *  \param[in] lsb_mode Encode bits in LSB orde instead of MSB
 *  \returns length in bytes (max written offset of output buffer + 1)
 */
int osmo_pbit2ubit_ext(ubit_t *out, unsigned int out_ofs,
                       const pbit_t *in, unsigned int in_ofs,
                       unsigned int num_bits, int lsb_mode)
{
	int i, ip, bn;
	for (i=0; i<num_bits; i++) {
		ip = in_ofs + i;
		bn = lsb_mode ? (ip&7) : (7-(ip&7));
		out[out_ofs+i] = !!(in[ip>>3] & (1<<bn));
	}
	return out_ofs + num_bits;
}

/*! generalized bit reversal function
 *  \param[in] x the 32bit value to be reversed
 *  \param[in] k the type of reversal requested
 *  \returns the reversed 32bit dword
 *
 * This function reverses the bit order within a 32bit word. Depending
 * on "k", it either reverses all bits in a 32bit dword, or the bytes in
 * the dword, or the bits in each byte of a dword, or simply swaps the
 * two 16bit words in a dword.  See Chapter 7 "Hackers Delight"
 */
uint32_t osmo_bit_reversal(uint32_t x, enum osmo_br_mode k)
{
	if (k &  1) x = (x & 0x55555555) <<  1 | (x & 0xAAAAAAAA) >>  1;
	if (k &  2) x = (x & 0x33333333) <<  2 | (x & 0xCCCCCCCC) >>  2;
	if (k &  4) x = (x & 0x0F0F0F0F) <<  4 | (x & 0xF0F0F0F0) >>  4;
	if (k &  8) x = (x & 0x00FF00FF) <<  8 | (x & 0xFF00FF00) >>  8;
	if (k & 16) x = (x & 0x0000FFFF) << 16 | (x & 0xFFFF0000) >> 16;

	return x;
}

/*! reverse the bit-order in each byte of a dword
 *  \param[in] x 32bit input value
 *  \returns 32bit value where bits of each byte have been reversed
 *
 * See Chapter 7 "Hackers Delight"
 */
uint32_t osmo_revbytebits_32(uint32_t x)
{
	x = (x & 0x55555555) <<  1 | (x & 0xAAAAAAAA) >>  1;
	x = (x & 0x33333333) <<  2 | (x & 0xCCCCCCCC) >>  2;
	x = (x & 0x0F0F0F0F) <<  4 | (x & 0xF0F0F0F0) >>  4;

	return x;
}

/*! reverse the bit order in a byte
 *  \param[in] x 8bit input value
 *  \returns 8bit value where bits order has been reversed
 *
 * See Chapter 7 "Hackers Delight"
 */
uint32_t osmo_revbytebits_8(uint8_t x)
{
	x = (x & 0x55) <<  1 | (x & 0xAA) >>  1;
	x = (x & 0x33) <<  2 | (x & 0xCC) >>  2;
	x = (x & 0x0F) <<  4 | (x & 0xF0) >>  4;

	return x;
}

/*! reverse bit-order of each byte in a buffer
 *  \param[in] buf buffer containing bytes to be bit-reversed
 *  \param[in] len length of buffer in bytes
 *
 *  This function reverses the bits in each byte of the buffer
 */
void osmo_revbytebits_buf(uint8_t *buf, int len)
{
	unsigned int i;
	unsigned int unaligned_cnt;
	int len_remain = len;

	unaligned_cnt = ((unsigned long)buf & 3);
	for (i = 0; i < unaligned_cnt; i++) {
		buf[i] = osmo_revbytebits_8(buf[i]);
		len_remain--;
		if (len_remain <= 0)
			return;
	}

	for (i = unaligned_cnt; i + 3 < len; i += 4) {
		osmo_store32be(osmo_revbytebits_32(osmo_load32be(buf + i)), buf + i);
		len_remain -= 4;
	}

	for (i = len - len_remain; i < len; i++) {
		buf[i] = osmo_revbytebits_8(buf[i]);
		len_remain--;
	}
}

/*! @} */