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+#ifndef DIVE_H
+#define DIVE_H
+
+/*
+ * Some silly typedefs to make our units very explicit.
+ *
+ * Also, the units are chosen so that values can be expressible as
+ * integers, so that we never have FP rounding issues. And they
+ * are small enough that converting to/from imperial units doesn't
+ * really matter.
+ *
+ * We also strive to make '0' a meaningless number saying "not
+ * initialized", since many values are things that may not have
+ * been reported (eg tank pressure or temperature from dive
+ * computers that don't support them). But sometimes -1 is an even
+ * more explicit way of saying "not there".
+ *
+ * Thus "millibar" for pressure, for example, or "millikelvin" for
+ * temperatures. Doing temperatures in celsius or fahrenheit would
+ * make for loss of precision when converting from one to the other,
+ * and using millikelvin is SI-like but also means that a temperature
+ * of '0' is clearly just a missing temperature or tank pressure.
+ *
+ * Also strive to use units that can not possibly be mistaken for a
+ * valid value in a "normal" system without conversion. If the max
+ * depth of a dive is '20000', you probably didn't convert from mm on
+ * output, or if the max depth gets reported as "0.2ft" it was either
+ * a really boring dive, or there was some missing input conversion,
+ * and a 60-ft dive got recorded as 60mm.
+ *
+ * Doing these as "structs containing value" means that we always
+ * have to explicitly write out those units in order to get at the
+ * actual value. So there is hopefully little fear of using a value
+ * in millikelvin as Fahrenheit by mistake.
+ *
+ * We don't actually use these all yet, so maybe they'll change, but
+ * I made a number of types as guidelines.
+ */
+typedef struct {
+	int seconds;
+} duration_t;
+
+typedef struct {
+	int mm;
+} depth_t;
+
+typedef struct {
+	int mbar;
+} pressure_t;
+
+typedef struct {
+	int mkelvin;
+} temperature_t;
+
+typedef struct {
+	int mliter;
+} volume_t;
+
+typedef struct {
+	int permille;
+} fraction_t;
+
+typedef struct {
+	int grams;
+} weight_t;
+
+typedef struct {
+	fraction_t o2;
+	fraction_t n2;
+	fraction_t he2;
+} gasmix_t;
+
+typedef struct {
+	volume_t size;
+	pressure_t pressure;
+} tank_type_t;
+
+static inline int to_feet(depth_t depth)
+{
+	return depth.mm * 0.00328084 + 0.5;
+}
+
+static inline int to_C(temperature_t temp)
+{
+	if (!temp.mkelvin)
+		return 0;
+	return (temp.mkelvin - 273150) / 1000;
+}
+
+static inline int to_PSI(pressure_t pressure)
+{
+	return pressure.mbar * 0.0145037738 + 0.5;
+}
+
+struct sample {
+	duration_t time;
+	depth_t depth;
+	temperature_t temperature;
+	pressure_t tankpressure;
+	int tankindex;
+};
+
+struct dive {
+	time_t when;
+	depth_t maxdepth, meandepth;
+	duration_t duration, surfacetime;
+	depth_t visibility;
+	temperature_t airtemp, watertemp;
+	pressure_t beginning_pressure, end_pressure;
+	int samples;
+	struct sample sample[];
+};
+
+#endif /* DIVE_H */