add osmo_bcd2str()

Add a standalone bcd-to-string conversion function with generic parameters.
Add a regression test in utils_test.c.

So far there is no single universal implementation that converts a BCD to a
string. I could only find gsm48_mi_to_string(), which also interprets
surrounding bytes, MI type and TMSI as non-BCD value.

The idea is to use this function from gsm48_mi_to_string() and similar
implementations in subsequent commits.

Root cause: in osmo-msc, I want to have an alternative MI-to-string function
for composing an FSM name, which needs the BCD part of gsm48_mi_to_string() but
not the TMSI part.

Change-Id: I86b09d37ceef33331c1a56046a5443127d6c6be0

include/osmocom/core/utils.h

@@ -49,6 +49,8 @@ char osmo_bcd2char(uint8_t bcd);
 /* only works for numbers in ascci */
 uint8_t osmo_char2bcd(char c);
 
+int osmo_bcd2str(char *dst, size_t dst_size, const uint8_t *bcd, int start_nibble, int end_nibble, bool allow_hex);
+
 int osmo_hexparse(const char *str, uint8_t *b, int max_len);
 
 char *osmo_ubit_dump(const uint8_t *bits, unsigned int len);

src/utils.c

@@ -129,6 +129,47 @@ uint8_t osmo_char2bcd(char c)
 		return 0;
 }
 
+/*! Convert BCD to string.
+ * The given nibble offsets are interpreted in BCD order, i.e. nibble 0 is bcd[0] & 0xf, nibble 1 is bcd[0] >> 4, nibble
+ * 3 is bcd[1] & 0xf, etc..
+ *  \param[out] dst  Output string buffer, is always nul terminated when dst_size > 0.
+ *  \param[in] dst_size  sizeof() the output string buffer.
+ *  \param[in] bcd  Binary coded data buffer.
+ *  \param[in] start_nibble  Offset to start from, in nibbles, typically 1 to skip the first nibble.
+ *  \param[in] end_nibble  Offset to stop before, in nibbles, e.g. sizeof(bcd) - (bcd[0] & GSM_MI_ODD? 0:1).
+ *  \param[in] allow_hex  If false, return error if there are digits other than 0-9. If true, return those as [A-F].
+ *  \returns The strlen that would be written if the output buffer is large enough, excluding nul byte (like
+ *           snprintf()), or -EINVAL if allow_hex is false and a digit > 9 is encountered. On -EINVAL, the conversion is
+ *           still completed as if allow_hex were passed as true. Return -ENOMEM if dst is NULL or dst_size is zero.
+ *           If end_nibble <= start_nibble, write an empty string to dst and return 0.
+ */
+int osmo_bcd2str(char *dst, size_t dst_size, const uint8_t *bcd, int start_nibble, int end_nibble, bool allow_hex)
+{
+	char *dst_end = dst + dst_size - 1;
+	int nibble_i;
+	int rc = 0;
+
+	if (!dst || dst_size < 1)
+		return -ENOMEM;
+
+	for (nibble_i = start_nibble; nibble_i < end_nibble && dst < dst_end; nibble_i++, dst++) {
+		uint8_t nibble = bcd[nibble_i >> 1];
+		if ((nibble_i & 1))
+			nibble >>= 4;
+		nibble &= 0xf;
+
+		if (!allow_hex && nibble > 9)
+			rc = -EINVAL;
+
+		*dst = osmo_bcd2char(nibble);
+	}
+	*dst = '\0';
+
+	if (rc < 0)
+		return rc;
+	return OSMO_MAX(0, end_nibble - start_nibble);
+}
+
 /*! Parse a string containing hexadecimal digits
  *  \param[in] str string containing ASCII encoded hexadecimal digits
  *  \param[out] b output buffer

tests/utils/utils_test.c

@@ -32,6 +32,7 @@
 #include <time.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
+#include <errno.h>
 
 static void hexdump_test(void)
 {
@@ -383,6 +384,118 @@ static void bcd_test(void)
 	}
 }
 
+struct bcd2str_test {
+	const char *bcd_hex;
+	int start_nibble;
+	int end_nibble;
+	bool allow_hex;
+	size_t str_size;
+	const char *expect_str;
+	int expect_rc;
+};
+
+static const struct bcd2str_test bcd2str_tests[] = {
+	{
+		.bcd_hex = "1a 32 54 76 98 f0",
+		.start_nibble = 1,
+		.end_nibble = 11,
+		.expect_str = "1234567890",
+		.expect_rc = 10,
+	},
+	{
+		.bcd_hex = "1a 32 a4 cb 9d f0",
+		.start_nibble = 1,
+		.end_nibble = 11,
+		.expect_str = "1234ABCD90",
+		.expect_rc = -EINVAL,
+	},
+	{
+		.bcd_hex = "1a 32 a4 cb 9d f0",
+		.start_nibble = 1,
+		.end_nibble = 11,
+		.allow_hex = true,
+		.expect_str = "1234ABCD90",
+		.expect_rc = 10,
+	},
+	{
+		.bcd_hex = "1a 32 54 76 98 f0",
+		.start_nibble = 1,
+		.end_nibble = 12,
+		.expect_str = "1234567890F",
+		.expect_rc = -EINVAL,
+	},
+	{
+		.bcd_hex = "1a 32 54 76 98 f0",
+		.start_nibble = 1,
+		.end_nibble = 12,
+		.allow_hex = true,
+		.expect_str = "1234567890F",
+		.expect_rc = 11,
+	},
+	{
+		.bcd_hex = "1a 32 54 76 98 f0",
+		.start_nibble = 0,
+		.end_nibble = 12,
+		.allow_hex = true,
+		.expect_str = "A1234567890F",
+		.expect_rc = 12,
+	},
+	{
+		.bcd_hex = "1a 32 54 76 98 f0",
+		.start_nibble = 1,
+		.end_nibble = 12,
+		.str_size = 5,
+		.expect_str = "1234",
+		.expect_rc = 11,
+	},
+	{
+		.bcd_hex = "",
+		.start_nibble = 1,
+		.end_nibble = 1,
+		.expect_str = "",
+		.expect_rc = 0,
+	},
+};
+
+static void bcd2str_test(void)
+{
+	int i;
+	uint8_t bcd[64];
+	int rc;
+
+	printf("\nTesting bcd to string conversion\n");
+
+	for (i = 0; i < ARRAY_SIZE(bcd2str_tests); i++) {
+		const struct bcd2str_test *t = &bcd2str_tests[i];
+		char str[64] = {};
+		size_t str_size = t->str_size ? : sizeof(str);
+
+		osmo_hexparse(t->bcd_hex, bcd, sizeof(bcd));
+
+		printf("- BCD-input='%s' nibbles=[%d..%d[ str_size=%zu\n", t->bcd_hex,
+		       t->start_nibble, t->end_nibble, str_size);
+		rc = osmo_bcd2str(str, str_size, bcd, t->start_nibble, t->end_nibble, t->allow_hex);
+
+		printf("  rc=%d\n", rc);
+
+		OSMO_ASSERT(str[str_size-1] == '\0');
+		printf("  -> %s\n", osmo_quote_str(str, -1));
+
+		if (rc != t->expect_rc)
+			printf("    ERROR: expected rc=%d\n", t->expect_rc);
+		if (strcmp(str, t->expect_str))
+			printf("    ERROR: expected result %s\n", osmo_quote_str(t->expect_str, -1));
+	}
+
+	printf("- zero output buffer\n");
+	rc = osmo_bcd2str(NULL, 100, bcd, 1, 2, false);
+	printf("  bcd2str(NULL, ...) -> %d\n", rc);
+	OSMO_ASSERT(rc < 0);
+	rc = osmo_bcd2str((char*)23, 0, bcd, 1, 2, false);
+	printf("  bcd2str(dst, 0, ...) -> %d\n", rc);
+	OSMO_ASSERT(rc < 0);
+}
+
 static void str_escape_test(void)
 {
 	int i;
@@ -810,6 +923,7 @@ int main(int argc, char **argv)
 	test_ipa_ccm_id_resp_parsing();
 	test_is_hexstr();
 	bcd_test();
+	bcd2str_test();
 	str_escape_test();
 	str_quote_test();
 	isqrt_test();

tests/utils/utils_test.ok

@@ -80,6 +80,35 @@ Testing BCD conversion
 	val=0xe, expected=E, found=E
 	val=0xf, expected=F, found=F
 
+Testing bcd to string conversion
+- BCD-input='1a 32 54 76 98 f0' nibbles=[1..11[ str_size=64
+  rc=10
+  -> "1234567890"
+- BCD-input='1a 32 a4 cb 9d f0' nibbles=[1..11[ str_size=64
+  rc=-22
+  -> "1234ABCD90"
+- BCD-input='1a 32 a4 cb 9d f0' nibbles=[1..11[ str_size=64
+  rc=10
+  -> "1234ABCD90"
+- BCD-input='1a 32 54 76 98 f0' nibbles=[1..12[ str_size=64
+  rc=-22
+  -> "1234567890F"
+- BCD-input='1a 32 54 76 98 f0' nibbles=[1..12[ str_size=64
+  rc=11
+  -> "1234567890F"
+- BCD-input='1a 32 54 76 98 f0' nibbles=[0..12[ str_size=64
+  rc=12
+  -> "A1234567890F"
+- BCD-input='1a 32 54 76 98 f0' nibbles=[1..12[ str_size=5
+  rc=11
+  -> "1234"
+- BCD-input='' nibbles=[1..1[ str_size=64
+  rc=0
+  -> ""
+- zero output buffer
+  bcd2str(NULL, ...) -> -12
+  bcd2str(dst, 0, ...) -> -12
+
 Testing string escaping
 - all chars from 0 to 255 in batches of 16:
 "\0\1\2\3\4\5\6\a\b\t\n\v\f\r\14\15"