Add pseudo-random bit sequence generator to libosmcoore

These PRBS sequences are specified in ITU-T O.150.  They are typically
used as test data to be transmitted for BER (bit error rate) testing.

Change-Id: I227b6a6e86a251460ecb816afa9a7439d5fb94d1

include/Makefile.am

@@ -31,6 +31,7 @@ nobase_include_HEADERS = \
                        osmocom/core/macaddr.h \
                        osmocom/core/msgb.h \
                        osmocom/core/panic.h \
+                       osmocom/core/prbs.h \
                        osmocom/core/prim.h \
                        osmocom/core/process.h \
                        osmocom/core/rate_ctr.h \

include/osmocom/core/prbs.h

@@ -0,0 +1,25 @@
+#pragma once
+#include <stdint.h>
+#include <osmocom/core/bits.h>
+
+/*! \brief definition of a PRBS sequence */
+struct osmo_prbs {
+	const char *name;	/*!< human-readable name */
+	unsigned int len;	/*!< length in bits */
+	uint64_t coeff;		/*!< coefficients */
+};
+
+/*! \brief state of a given PRBS sequence generator */
+struct osmo_prbs_state {
+	const struct osmo_prbs *prbs;
+	uint64_t state;
+};
+
+extern const struct osmo_prbs osmo_prbs7;
+extern const struct osmo_prbs osmo_prbs9;
+extern const struct osmo_prbs osmo_prbs11;
+extern const struct osmo_prbs osmo_prbs15;
+
+void osmo_prbs_state_init(struct osmo_prbs_state *st, const struct osmo_prbs *prbs);
+ubit_t osmo_prbs_get_ubit(struct osmo_prbs_state *state);
+int osmo_prbs_get_ubits(ubit_t *out, unsigned int out_len, struct osmo_prbs_state *state);

src/Makefile.am

@@ -21,7 +21,7 @@ libosmocore_la_SOURCES = timer.c timer_gettimeofday.c select.c signal.c msgb.c b
 			 conv.c application.c rbtree.c strrb.c \
 			 loggingrb.c crc8gen.c crc16gen.c crc32gen.c crc64gen.c \
 			 macaddr.c stat_item.c stats.c stats_statsd.c prim.c \
-			 conv_acc.c conv_acc_generic.c sercomm.c
+			 conv_acc.c conv_acc_generic.c sercomm.c prbs.c
 
 if HAVE_SSE3
 libosmocore_la_SOURCES += conv_acc_sse.c

src/prbs.c

@@ -0,0 +1,74 @@
+/* Osmocom implementation of pseudo-random bit sequence generation */
+/* (C) 2017 by Harald Welte <laforge@gnumonks.org> */
+
+#include <stdint.h>
+#include <string.h>
+#include <osmocom/core/bits.h>
+#include <osmocom/core/prbs.h>
+
+/*! \brief PRBS-7 according ITU-T O.150 */
+const struct osmo_prbs osmo_prbs7 = {
+	/* x^7 + x^6 + 1 */
+	.name = "PRBS-7",
+	.len = 7,
+	.coeff = (1<<6) | (1<<5),
+};
+
+/*! \brief PRBS-9 according ITU-T O.150 */
+const struct osmo_prbs osmo_prbs9 = {
+	/* x^9 + x^5 + 1 */
+	.name = "PRBS-9",
+	.len = 9,
+	.coeff = (1<<8) | (1<<4),
+};
+
+/*! \brief PRBS-11 according ITU-T O.150 */
+const struct osmo_prbs osmo_prbs11 = {
+	/* x^11 + x^9 + 1 */
+	.name = "PRBS-11",
+	.len = 11,
+	.coeff = (1<<10) | (1<<8),
+};
+
+/*! \brief PRBS-15 according ITU-T O.150 */
+const struct osmo_prbs osmo_prbs15 = {
+	/* x^15 + x^14+ 1 */
+	.name = "PRBS-15",
+	.len = 15,
+	.coeff = (1<<14) | (1<<13),
+};
+
+/*! \brief Initialize the given caller-allocated PRBS state */
+void osmo_prbs_state_init(struct osmo_prbs_state *st, const struct osmo_prbs *prbs)
+{
+	memset(st, 0, sizeof(*st));
+	st->prbs = prbs;
+	st->state = 1;
+}
+
+static void osmo_prbs_process_bit(struct osmo_prbs_state *state, ubit_t bit)
+{
+	state->state >>= 1;
+	if (bit)
+		state->state ^= state->prbs->coeff;
+}
+
+/*! \brief Get the next bit out of given PRBS instance */
+ubit_t osmo_prbs_get_ubit(struct osmo_prbs_state *state)
+{
+	ubit_t result = state->state & 0x1;
+	osmo_prbs_process_bit(state, result);
+
+	return result;
+}
+
+/*! \brief Fill buffer of unpacked bits with next bits out of given PRBS instance */
+int osmo_prbs_get_ubits(ubit_t *out, unsigned int out_len, struct osmo_prbs_state *state)
+{
+	unsigned int i;
+
+	for (i = 0; i < out_len; i++)
+		out[i] = osmo_prbs_get_ubit(state);
+
+	return i;
+}

tests/Makefile.am

@@ -15,7 +15,7 @@ check_PROGRAMS = timer/timer_test sms/sms_test ussd/ussd_test		\
 		 write_queue/wqueue_test socket/socket_test		\
 		 coding/coding_test conv/conv_gsm0503_test		\
 		 abis/abis_test endian/endian_test sercomm/sercomm_test	\
-		 stats/stats_test
+		 stats/stats_test prbs/prbs_test
 
 if ENABLE_MSGFILE
 check_PROGRAMS += msgfile/msgfile_test
@@ -183,6 +183,9 @@ endian_endian_test_LDADD = $(top_builddir)/src/libosmocore.la
 sercomm_sercomm_test_SOURCES = sercomm/sercomm_test.c
 sercomm_sercomm_test_LDADD = $(top_builddir)/src/libosmocore.la
 
+prbs_prbs_test_SOURCES = prbs/prbs_test.c
+prbs_prbs_test_LDADD = $(top_builddir)/src/libosmocore.la
+
 # The `:;' works around a Bash 3.2 bug when the output is not writeable.
 $(srcdir)/package.m4: $(top_srcdir)/configure.ac
 	:;{ \
@@ -226,7 +229,7 @@ EXTRA_DIST = testsuite.at $(srcdir)/package.m4 $(TESTSUITE)		\
 	     osmo-auc-gen/osmo-auc-gen_test.ok				\
 	     osmo-auc-gen/osmo-auc-gen_test.err				\
 	     conv/conv_gsm0503_test.ok endian/endian_test.ok 		\
-	     sercomm/sercomm_test.ok
+	     sercomm/sercomm_test.ok prbs/prbs_test.ok
 
 DISTCLEANFILES = atconfig atlocal conv/gsm0503_test_vectors.c
 BUILT_SOURCES = conv/gsm0503_test_vectors.c

tests/prbs/prbs_test.c

@@ -0,0 +1,47 @@
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <osmocom/core/prbs.h>
+
+static void dump_bits(const ubit_t *bits, unsigned int num_bits)
+{
+	unsigned int i;
+
+	for (i = 0; i < num_bits; i++) {
+		if (bits[i])
+			fputc('1', stdout);
+		else
+			fputc('0', stdout);
+	}
+	fputc('\n',stdout);
+}
+
+static void test_prbs(const struct osmo_prbs *prbs)
+{
+	struct osmo_prbs_state st;
+	unsigned int i;
+
+	printf("Testing PRBS sequence generation '%s'\n", prbs->name);
+	osmo_prbs_state_init(&st, prbs);
+
+	/* 2 lines */
+	for (i = 0; i < 2; i++) {
+		unsigned int seq_len = (1 << prbs->len)-1;
+		ubit_t bits[seq_len];
+		memset(bits, 0, sizeof(bits));
+		osmo_prbs_get_ubits(bits, sizeof(bits), &st);
+		dump_bits(bits, sizeof(bits));
+	}
+
+	printf("\n");
+}
+
+int main(int argc, char **argv)
+{
+	test_prbs(&osmo_prbs7);
+	test_prbs(&osmo_prbs9);
+	test_prbs(&osmo_prbs11);
+	test_prbs(&osmo_prbs15);
+
+	exit(0);
+}

tests/testsuite.at

@@ -280,3 +280,9 @@ AT_KEYWORDS([sercomm])
 cat $abs_srcdir/sercomm/sercomm_test.ok > expout
 AT_CHECK([$abs_top_builddir/tests/sercomm/sercomm_test], [0], [expout], [ignore])
 AT_CLEANUP
+
+AT_SETUP([prbs])
+AT_KEYWORDS([prbs])
+cat $abs_srcdir/prbs/prbs_test.ok > expout
+AT_CHECK([$abs_top_builddir/tests/prbs/prbs_test], [0], [expout], [ignore])
+AT_CLEANUP