drivers: Fix locale dependent string to float conversion

Some drivers used locale dependent functions for converting strings
to float/double values. These functions fail when the decimal mark
is a "," in the locale settings but the string contains a ".".

This fixes bug #1064.

src/dmm/m2110.c

@@ -44,7 +44,7 @@ SR_PRIV gboolean sr_m2110_packet_valid(const uint8_t *buf)
 	if (!strncmp((const char *)buf, "OVERRNG", 7))
 		return TRUE;
 
-	if (sscanf((const char *)buf, "%f", &val) == 1)
+	if (sr_atof_ascii((const char *)buf, &val) == SR_OK)
 		return TRUE;
 	else
 		return FALSE;
@@ -65,7 +65,7 @@ SR_PRIV int sr_m2110_parse(const uint8_t *buf, float *floatval,
 
 	if (!strncmp((const char *)buf, "OVERRNG", 7))
 		*floatval = INFINITY;
-	else if (sscanf((const char *)buf, "%f", &val) == 1) {
+	else if (sr_atof_ascii((const char *)buf, &val) == SR_OK) {
 		*floatval = val;
 		dot_pos = strcspn((const char *)buf, ".");
 		if (dot_pos < 7)

src/dmm/metex14.c

@@ -86,7 +86,7 @@ static int parse_value(const uint8_t *buf, struct metex14_info *info,
 		return SR_OK;
 
 	/* Bytes 2-8: Sign, value (up to 5 digits) and decimal point */
-	sscanf((const char *)&valstr, "%f", result);
+	sr_atof_ascii((const char *)&valstr, result);
 
 	dot_pos = strcspn(valstr, ".");
 	if (dot_pos < cnt)

src/hardware/motech-lps-30x/protocol.c

@@ -87,7 +87,7 @@ static void process_line(struct sr_dev_inst *sdi)
 		case AQ_U2:
 		case AQ_I1:
 		case AQ_I2:
-			if (sr_atod(devc->buf, &dbl) != SR_OK) {
+			if (sr_atod_ascii(devc->buf, &dbl) != SR_OK) {
 				sr_err("Failed to convert '%s' to double, errno=%d %s",
 					devc->buf, errno, g_strerror(errno));
 				dbl = 0.0;

src/libsigrok-internal.h

@@ -1010,6 +1010,7 @@ SR_PRIV int sr_atol(const char *str, long *ret);
 SR_PRIV int sr_atoi(const char *str, int *ret);
 SR_PRIV int sr_atod(const char *str, double *ret);
 SR_PRIV int sr_atof(const char *str, float *ret);
+SR_PRIV int sr_atod_ascii(const char *str, double *ret);
 SR_PRIV int sr_atof_ascii(const char *str, float *ret);
 
 /*--- soft-trigger.c --------------------------------------------------------*/

src/scpi/scpi.c

@@ -627,7 +627,7 @@ SR_PRIV int sr_scpi_get_double(struct sr_scpi_dev_inst *scpi,
 	if (ret != SR_OK && !response)
 		return ret;
 
-	if (sr_atod(response, scpi_response) == SR_OK)
+	if (sr_atod_ascii(response, scpi_response) == SR_OK)
 		ret = SR_OK;
 	else
 		ret = SR_ERR_DATA;

src/strutil.c

@@ -169,6 +169,38 @@ SR_PRIV int sr_atof(const char *str, float *ret)
 	return SR_OK;
 }
 
+/**
+ * @private
+ *
+ * Convert a string representation of a numeric value to a double. The
+ * conversion is strict and will fail if the complete string does not represent
+ * a valid double. The function sets errno according to the details of the
+ * failure. This version ignores the locale.
+ *
+ * @param str The string representation to convert.
+ * @param ret Pointer to double where the result of the conversion will be stored.
+ *
+ * @retval SR_OK Conversion successful.
+ * @retval SR_ERR Failure.
+ */
+SR_PRIV int sr_atod_ascii(const char *str, double *ret)
+{
+	double tmp;
+	char *endptr = NULL;
+
+	errno = 0;
+	tmp = g_ascii_strtod(str, &endptr);
+
+	if (!endptr || *endptr || errno) {
+		if (!errno)
+			errno = EINVAL;
+		return SR_ERR;
+	}
+
+	*ret = tmp;
+	return SR_OK;
+}
+
 /**
  * @private
  *