bitvec: Add get/set byte sequences

The new functions bitvec_get_bytes and bitvec_set_bytes copy
byte sequences from bitvecs to uint8_t arrays and vice versa.
While the bytes in the bitvecs do not need to be aligned, the uint8_t
arrays always are. In case the bytes in the bitvec are aligned, the
implementation uses memcpy.

Note that the implementation like the other existing functions assume
MSB first encoding.

[hfreyther: Squash the comment fix into this commit as well]

Sponsored-by: On-Waves ehf

include/osmocom/core/bitvec.h

@@ -28,6 +28,14 @@
 
 /*! \file bitvec.h
  *  \brief Osmocom bit vector abstraction
+ *
+ *  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).
  */
 
 #include <stdint.h>
@@ -63,5 +71,7 @@ int bitvec_set_uint(struct bitvec *bv, unsigned int in, int count);
 int bitvec_get_uint(struct bitvec *bv, int num_bits);
 int bitvec_find_bit_pos(const struct bitvec *bv, unsigned int n, enum bit_value val);
 int bitvec_spare_padding(struct bitvec *bv, unsigned int up_to_bit);
+int bitvec_get_bytes(struct bitvec *bv, uint8_t *bytes, int count);
+int bitvec_set_bytes(struct bitvec *bv, const uint8_t *bytes, int count);
 
 /*! @} */

src/bitvec.c

@@ -1,6 +1,7 @@
 /* bit vector utility routines */
 
 /* (C) 2009 by Harald Welte <laforge@gnumonks.org>
+ * (C) 2015 by Sysmocom s.f.m.c. GmbH
  *
  * All Rights Reserved
  *
@@ -30,6 +31,7 @@
 
 #include <errno.h>
 #include <stdint.h>
+#include <string.h>
 
 #include <osmocom/core/bitvec.h>
 
@@ -261,4 +263,77 @@ int bitvec_find_bit_pos(const struct bitvec *bv, unsigned int n,
 	return -1;
 }
 
+/*! \brief 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
+ */
+int bitvec_get_bytes(struct bitvec *bv, uint8_t *bytes, 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;
+}
+
+/*! \brief 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
+ */
+int bitvec_set_bytes(struct bitvec *bv, const uint8_t *bytes, 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;
+}
 /*! @} */

tests/Makefile.am

@@ -11,7 +11,8 @@ check_PROGRAMS = timer/timer_test sms/sms_test ussd/ussd_test		\
 		 logging/logging_test fr/fr_test			\
 		 loggingrb/loggingrb_test strrb/strrb_test              \
 		 vty/vty_test comp128/comp128_test utils/utils_test	\
-		 smscb/gsm0341_test stats/stats_test
+		 smscb/gsm0341_test stats/stats_test			\
+		 bitvec/bitvec_test
 
 if ENABLE_MSGFILE
 check_PROGRAMS += msgfile/msgfile_test
@@ -38,6 +39,9 @@ auth_milenage_test_LDADD = $(top_builddir)/src/libosmocore.la $(top_builddir)/sr
 bits_bitrev_test_SOURCES = bits/bitrev_test.c
 bits_bitrev_test_LDADD = $(top_builddir)/src/libosmocore.la
 
+bitvec_bitvec_test_SOURCES = bitvec/bitvec_test.c
+bitvec_bitvec_test_LDADD = $(top_builddir)/src/libosmocore.la
+
 conv_conv_test_SOURCES = conv/conv_test.c
 conv_conv_test_LDADD = $(top_builddir)/src/libosmocore.la
 
@@ -128,7 +132,8 @@ EXTRA_DIST = testsuite.at $(srcdir)/package.m4 $(TESTSUITE)		\
              fr/fr_test.ok loggingrb/logging_test.ok			\
              loggingrb/logging_test.err	strrb/strrb_test.ok		\
 	     vty/vty_test.ok comp128/comp128_test.ok			\
-	     utils/utils_test.ok stats/stats_test.ok
+	     utils/utils_test.ok stats/stats_test.ok			\
+	     bitvec/bitvec_test.ok
 
 DISTCLEANFILES = atconfig
 

tests/bitvec/bitvec_test.c

@@ -0,0 +1,62 @@
+#include <inttypes.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+
+#include <osmocom/core/utils.h>
+#include <osmocom/core/bitvec.h>
+
+static void test_byte_ops()
+{
+	struct bitvec bv;
+	const uint8_t *in = (const uint8_t *)"ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+	uint8_t out[26 + 2];
+	uint8_t data[64];
+	int i;
+	int rc;
+	int in_size = strlen((const char *)in);
+
+	printf("=== start %s ===\n", __func__);
+
+	bv.data = data;
+	bv.data_len = sizeof(data);
+
+	for (i = 0; i < 32; i++) {
+		/* Write to bitvec */
+		memset(data, 0x00, sizeof(data));
+		bv.cur_bit = i;
+		rc = bitvec_set_uint(&bv, 0x7e, 8);
+		OSMO_ASSERT(rc >= 0);
+		rc = bitvec_set_bytes(&bv, in, in_size);
+		OSMO_ASSERT(rc >= 0);
+		rc = bitvec_set_uint(&bv, 0x7e, 8);
+		OSMO_ASSERT(rc >= 0);
+
+		fprintf(stderr, "bitvec: %s\n", osmo_hexdump(bv.data, bv.data_len));
+
+		/* Read from bitvec */
+		memset(out, 0xff, sizeof(out));
+		bv.cur_bit = i;
+		rc = bitvec_get_uint(&bv, 8);
+		OSMO_ASSERT(rc == 0x7e);
+		rc = bitvec_get_bytes(&bv, out + 1, in_size);
+		OSMO_ASSERT(rc >= 0);
+		rc = bitvec_get_uint(&bv, 8);
+		OSMO_ASSERT(rc == 0x7e);
+
+		fprintf(stderr, "out: %s\n", osmo_hexdump(out, sizeof(out)));
+
+		OSMO_ASSERT(out[0] == 0xff);
+		OSMO_ASSERT(out[in_size+1] == 0xff);
+		OSMO_ASSERT(memcmp(in, out + 1, in_size) == 0);
+	}
+
+	printf("=== end %s ===\n", __func__);
+}
+
+int main(int argc, char **argv)
+{
+	test_byte_ops();
+	return 0;
+}

tests/bitvec/bitvec_test.ok

@@ -0,0 +1,2 @@
+=== start test_byte_ops ===
+=== end test_byte_ops ===

tests/testsuite.at

@@ -21,6 +21,12 @@ cat $abs_srcdir/bits/bitrev_test.ok > expout
 AT_CHECK([$abs_top_builddir/tests/bits/bitrev_test], [0], [expout])
 AT_CLEANUP
 
+AT_SETUP([bitvec])
+AT_KEYWORDS([bitvec])
+cat $abs_srcdir/bitvec/bitvec_test.ok > expout
+AT_CHECK([$abs_top_builddir/tests/bitvec/bitvec_test], [0], [expout], [ignore])
+AT_CLEANUP
+
 AT_SETUP([conv])
 AT_KEYWORDS([conv])
 cat $abs_srcdir/conv/conv_test.ok > expout