Move unit related code to units.h

The units are used everywhere in the application, we don't really
need to include "dive.h" to be able to use unit conversion, so I
changed them to a new file. There is still a lot of non-dive stuff
in dive.h / c, I'll try to move more later.

Signed-off-by: Tomaz Canabrava <tomaz.canabrava@intel.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

1 files changed, 243 insertions, 0 deletions

diff --git a/units.h b/units.h
new file mode 100644
index 000000000..0e168a21e
--- /dev/null
+++ b/units.h
@@ -0,0 +1,243 @@
+#ifndef UNITS_H
+#define UNITS_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define O2_IN_AIR 209 // permille
+#define N2_IN_AIR 781
+#define O2_DENSITY 1429 // mg/Liter
+#define N2_DENSITY 1251
+#define HE_DENSITY 179
+#define SURFACE_PRESSURE 1013 // mbar
+#define SURFACE_PRESSURE_STRING "1013"
+#define ZERO_C_IN_MKELVIN 273150 // mKelvin
+
+/* Salinity is expressed in weight in grams per 10l */
+#define SEAWATER_SALINITY 10300
+#define FRESHWATER_SALINITY 10000
+
+/*
+ * 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 cylinder 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 cylinder 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 int64_t timestamp_t;
+
+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
+{
+	int udeg;
+} degrees_t;
+
+static inline double grams_to_lbs(int grams)
+{
+	return grams / 453.6;
+}
+
+static inline int lbs_to_grams(double lbs)
+{
+	return rint(lbs * 453.6);
+}
+
+static inline double ml_to_cuft(int ml)
+{
+	return ml / 28316.8466;
+}
+
+static inline double cuft_to_l(double cuft)
+{
+	return cuft * 28.3168466;
+}
+
+static inline double mm_to_feet(int mm)
+{
+	return mm * 0.00328084;
+}
+
+static inline unsigned long feet_to_mm(double feet)
+{
+	return rint(feet * 304.8);
+}
+
+static inline int to_feet(depth_t depth)
+{
+	return rint(mm_to_feet(depth.mm));
+}
+
+static inline double mkelvin_to_C(int mkelvin)
+{
+	return (mkelvin - ZERO_C_IN_MKELVIN) / 1000.0;
+}
+
+static inline double mkelvin_to_F(int mkelvin)
+{
+	return mkelvin * 9 / 5000.0 - 459.670;
+}
+
+static inline unsigned long F_to_mkelvin(double f)
+{
+	return rint((f - 32) * 1000 / 1.8 + ZERO_C_IN_MKELVIN);
+}
+
+static inline unsigned long C_to_mkelvin(double c)
+{
+	return rint(c * 1000 + ZERO_C_IN_MKELVIN);
+}
+
+static inline double psi_to_bar(double psi)
+{
+	return psi / 14.5037738;
+}
+
+static inline long psi_to_mbar(double psi)
+{
+	return rint(psi_to_bar(psi) * 1000);
+}
+
+static inline int to_PSI(pressure_t pressure)
+{
+	return rint(pressure.mbar * 0.0145037738);
+}
+
+static inline double bar_to_atm(double bar)
+{
+	return bar / SURFACE_PRESSURE * 1000;
+}
+
+static inline double mbar_to_atm(int mbar)
+{
+	return (double)mbar / SURFACE_PRESSURE;
+}
+
+static inline int mbar_to_PSI(int mbar)
+{
+	pressure_t p = { mbar };
+	return to_PSI(p);
+}
+
+/*
+ * We keep our internal data in well-specified units, but
+ * the input and output may come in some random format. This
+ * keeps track of those units.
+ */
+/* turns out in Win32 PASCAL is defined as a calling convention */
+#ifdef WIN32
+#undef PASCAL
+#endif
+struct units {
+	enum {
+		METERS,
+		FEET
+	} length;
+	enum {
+		LITER,
+		CUFT
+	} volume;
+	enum {
+		BAR,
+		PSI,
+		PASCAL
+	} pressure;
+	enum {
+		CELSIUS,
+		FAHRENHEIT,
+		KELVIN
+	} temperature;
+	enum {
+		KG,
+		LBS
+	} weight;
+	enum {
+		SECONDS,
+		MINUTES
+	} vertical_speed_time;
+};
+
+/*
+ * We're going to default to SI units for input. Yes,
+ * technically the SI unit for pressure is Pascal, but
+ * we default to bar (10^5 pascal), which people
+ * actually use. Similarly, C instead of Kelvin.
+ * And kg instead of g.
+ */
+#define SI_UNITS                                                                                                                         \
+	{                                                                                                                                \
+		.length = METERS, .volume = LITER, .pressure = BAR, .temperature = CELSIUS, .weight = KG, .vertical_speed_time = MINUTES \
+	}
+
+#define IMPERIAL_UNITS                                                                                                                    \
+	{                                                                                                                                 \
+		.length = FEET, .volume = CUFT, .pressure = PSI, .temperature = FAHRENHEIT, .weight = LBS, .vertical_speed_time = MINUTES \
+	}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
\ No newline at end of file