Use a layout descriptor with a generic decode function

Replace hardcoded constants with a layout descriptor. This reduces the
amount of model specific conditions, and makes it easier to add support
for new models.

The Cressi data format uses nibbles (4 bits) as the smallest unit of
storage. Larger values are stored as one or more nibble, typically with
a BCD (binary coded decimal) encoding applied. To decode such variable
sized numbers, a generic function is added. The offsets in the layout
descriptor are also specified in nibbles instead of bytes.

Author: jefdriesen

src/cressi_edy_parser.c

@@ -35,9 +35,22 @@
 
 typedef struct cressi_edy_parser_t cressi_edy_parser_t;
 
+typedef struct cressi_edy_layout_t {
+	unsigned int datetime_y;
+	unsigned int datetime_md;
+	unsigned int datetime_hm;
+	unsigned int avgdepth;
+	unsigned int maxdepth;
+	unsigned int temperature;
+	unsigned int divetime;
+	unsigned int gasmix;
+	unsigned int gasmix_count;
+} cressi_edy_layout_t;
+
 struct cressi_edy_parser_t {
 	dc_parser_t base;
 	unsigned int model;
+	const cressi_edy_layout_t *layout;
 };
 
 static dc_status_t cressi_edy_parser_get_datetime (dc_parser_t *abstract, dc_datetime_t *datetime);
@@ -56,16 +69,50 @@ static const dc_parser_vtable_t cressi_edy_parser_vtable = {
 	NULL /* destroy */
 };
 
+static const cressi_edy_layout_t edy = {
+	 8, /* datetime_y */
+	10, /* datetime_md */
+	28, /* datetime_hm */
+	 1, /* avgdepth */
+	 5, /* maxdepth */
+	22, /* temperature */
+	25, /* divetime */
+	46, 3, /* gasmix */
+};
+
+static unsigned int
+decode (const unsigned char data[], unsigned int offset, unsigned int n)
+{
+	unsigned int result = 0;
+
+	for (unsigned int i = 0; i < n; ++i) {
+		unsigned char byte = data[offset / 2];
+
+		unsigned char nibble = 0;
+		if ((offset & 1) == 0) {
+			nibble = (byte >> 4) & 0x0F;
+		} else {
+			nibble = byte & 0x0F;
+		}
+
+		result *= 10;
+		result += nibble;
+		offset++;
+	}
+
+	return result;
+}
 
 static unsigned int
-cressi_edy_parser_count_gasmixes (const unsigned char *data)
+cressi_edy_parser_count_gasmixes (const unsigned char data[], const cressi_edy_layout_t *layout)
 {
 	// Count the number of active gas mixes. The active gas
 	// mixes are always first, so we stop counting as soon
 	// as the first gas marked as disabled is found.
 	unsigned int i = 0;
-	while (i < 3) {
-		if ((data[0x17 - i] & 0xF0) == 0xF0)
+	while (i < layout->gasmix_count) {
+		unsigned int state = decode(data, layout->gasmix - i * 2, 1);
+		if (state == 0x0F)
 			break;
 		i++;
 	}
@@ -89,6 +136,7 @@ cressi_edy_parser_create (dc_parser_t **out, dc_context_t *context, const unsign
 
 	// Set the default values.
 	parser->model = model;
+	parser->layout = &edy;
 
 	*out = (dc_parser_t*) parser;
 
@@ -99,17 +147,19 @@ cressi_edy_parser_create (dc_parser_t **out, dc_context_t *context, const unsign
 static dc_status_t
 cressi_edy_parser_get_datetime (dc_parser_t *abstract, dc_datetime_t *datetime)
 {
+	cressi_edy_parser_t *parser = (cressi_edy_parser_t *) abstract;
+	const cressi_edy_layout_t *layout = parser->layout;
+	const unsigned char *data = abstract->data;
+
 	if (abstract->size < SZ_HEADER)
 		return DC_STATUS_DATAFORMAT;
 
-	const unsigned char *p = abstract->data;
-
 	if (datetime) {
-		datetime->year = bcd2dec (p[4]) + 2000;
-		datetime->month = (p[5] & 0xF0) >> 4;
-		datetime->day = (p[5] & 0x0F) * 10 + ((p[6] & 0xF0) >> 4);
-		datetime->hour = bcd2dec (p[14]);
-		datetime->minute = bcd2dec (p[15]);
+		datetime->year   = decode(data, layout->datetime_y, 2) + 2000;
+		datetime->month  = decode(data, layout->datetime_md, 1);
+		datetime->day    = decode(data, layout->datetime_md + 1, 2);
+		datetime->hour   = decode(data, layout->datetime_hm, 2);
+		datetime->minute = decode(data, layout->datetime_hm + 2, 2);
 		datetime->second = 0;
 		datetime->timezone = DC_TIMEZONE_NONE;
 	}
@@ -122,39 +172,39 @@ static dc_status_t
 cressi_edy_parser_get_field (dc_parser_t *abstract, dc_field_type_t type, unsigned int flags, void *value)
 {
 	cressi_edy_parser_t *parser = (cressi_edy_parser_t *) abstract;
+	const cressi_edy_layout_t *layout = parser->layout;
+	const unsigned char *data = abstract->data;
 
 	if (abstract->size < SZ_HEADER)
 		return DC_STATUS_DATAFORMAT;
 
-	const unsigned char *p = abstract->data;
-
 	dc_gasmix_t *gasmix = (dc_gasmix_t *) value;
 
 	if (value) {
 		switch (type) {
 		case DC_FIELD_DIVETIME:
 			if (parser->model == EDY)
-				*((unsigned int *) value) = bcd2dec (p[0x0C] & 0x0F) * 60 + bcd2dec (p[0x0D]);
+				*((unsigned int *) value) = decode(data, layout->divetime, 1) * 60 + decode(data, layout->divetime + 1, 2);
 			else
-				*((unsigned int *) value) = (bcd2dec (p[0x0C] & 0x0F) * 100 + bcd2dec (p[0x0D])) * 60;
+				*((unsigned int *) value) = decode(data, layout->divetime, 3) * 60;
 			break;
 		case DC_FIELD_MAXDEPTH:
-			*((double *) value) = (bcd2dec (p[0x02] & 0x0F) * 100 + bcd2dec (p[0x03])) / 10.0;
+			*((double *) value) = decode(data, layout->maxdepth, 3) / 10.0;
 			break;
 		case DC_FIELD_AVGDEPTH:
-			*((double *) value) = (bcd2dec (p[0x00] & 0x0F) * 100 + bcd2dec (p[0x01])) / 10.0;
+			*((double *) value) = decode(data, layout->avgdepth, 3) / 10.0;
 			break;
 		case DC_FIELD_GASMIX_COUNT:
-			*((unsigned int *) value) = cressi_edy_parser_count_gasmixes(p);
+			*((unsigned int *) value) = cressi_edy_parser_count_gasmixes(data, layout);
 			break;
 		case DC_FIELD_GASMIX:
 			gasmix->usage = DC_USAGE_NONE;
 			gasmix->helium = 0.0;
-			gasmix->oxygen = bcd2dec (p[0x17 - flags]) / 100.0;
+			gasmix->oxygen = decode(data, layout->gasmix - flags * 2, 2) / 100.0;
 			gasmix->nitrogen = 1.0 - gasmix->oxygen - gasmix->helium;
 			break;
 		case DC_FIELD_TEMPERATURE_MINIMUM:
-			*((double *) value) = (bcd2dec (p[0x0B]) * 10 + ((p[0x0C] & 0xF0) >> 4)) / 10.0;
+			*((double *) value) = decode(data, layout->temperature, 3) / 10.0;
 			break;
 		default:
 			return DC_STATUS_UNSUPPORTED;
@@ -169,6 +219,7 @@ static dc_status_t
 cressi_edy_parser_samples_foreach (dc_parser_t *abstract, dc_sample_callback_t callback, void *userdata)
 {
 	cressi_edy_parser_t *parser = (cressi_edy_parser_t *) abstract;
+	const cressi_edy_layout_t *layout = parser->layout;
 
 	const unsigned char *data = abstract->data;
 	unsigned int size = abstract->size;
@@ -182,7 +233,7 @@ cressi_edy_parser_samples_foreach (dc_parser_t *abstract, dc_sample_callback_t c
 			interval = 15;
 	}
 
-	unsigned int ngasmixes = cressi_edy_parser_count_gasmixes(data);
+	unsigned int ngasmixes = cressi_edy_parser_count_gasmixes(data, layout);
 	unsigned int gasmix = 0xFFFFFFFF;
 
 	unsigned int offset = SZ_HEADER;
@@ -202,7 +253,7 @@ cressi_edy_parser_samples_foreach (dc_parser_t *abstract, dc_sample_callback_t c
 		if (callback) callback (DC_SAMPLE_TIME, &sample, userdata);
 
 		// Depth (1/10 m).
-		unsigned int depth = bcd2dec (data[offset + 0] & 0x0F) * 100 + bcd2dec (data[offset + 1]);
+		unsigned int depth = decode(data + offset, 1, 3);
 		sample.depth = depth / 10.0;
 		if (callback) callback (DC_SAMPLE_DEPTH, &sample, userdata);