EAD and END: Treat trivial cases separately

If there is no helium the breathing mix, the END is just the current
depth. Simiarly for air and the EAD. Treating these trivial cases
separately makes sure there are no rounding problems happening
when doing consecutive multiplication and division by the same
floating point number.

Signed-off-by: Robert C. Helling <helling@atdotde.de>

core/profile.c

@@ -1243,8 +1243,8 @@ static void calculate_gas_information_new(const struct dive *dive, const struct
 		amb_pressure = depth_to_bar(entry->depth, dive);
 		current_divemode = get_current_divemode(dc, entry->sec, &evd, &current_divemode);
 		fill_pressures(&entry->pressures, amb_pressure, gasmix, (current_divemode == OC) ? 0.0 : entry->o2pressure.mbar / 1000.0, current_divemode);
-		fn2 = (1000.0 * entry->pressures.n2 / amb_pressure);
-		fhe = (1000.0 * entry->pressures.he / amb_pressure);
+		fn2 = 1000.0 * entry->pressures.n2 / amb_pressure;
+		fhe = 1000.0 * entry->pressures.he / amb_pressure;
 		if (dc->divemode == PSCR) { // OC pO2 is calulated for PSCR with or without external PO2 monitoring.
 			struct gasmix gasmix2 = get_gasmix(dive, dc, entry->sec, &evg, gasmix);
 			entry->scr_OC_pO2.mbar = (int) depth_to_mbar(entry->depth, dive) * get_o2(gasmix2) / 1000;
@@ -1256,8 +1256,16 @@ static void calculate_gas_information_new(const struct dive *dive, const struct
 		 * EAD just uses N₂ ("Air" for nitrox dives) */
 		pressure_t modpO2 = { .mbar = (int)(prefs.modpO2 * 1000) };
 		entry->mod = gas_mod(gasmix, modpO2, dive, 1).mm;
-		entry->end = mbar_to_depth((int)(depth_to_mbarf(entry->depth, dive) * (1000 - fhe) / 1000.0), dive);
-		entry->ead = mbar_to_depth((int)(depth_to_mbarf(entry->depth, dive) * fn2 / (double)N2_IN_AIR), dive);
+		// Make shure there trivial cases get the right answer and there are no floating point mishaps
+		if (entry->pressures.he)
+			entry->end = mbar_to_depth((int)(depth_to_mbarf(entry->depth, dive) * (1000 - fhe) / 1000.0), dive);
+		else
+			entry->end = entry->depth;
+
+		if (gasmix_is_air(gasmix))
+			entry->ead = entry->depth;
+		else
+			entry->ead = mbar_to_depth((int)(depth_to_mbarf(entry->depth, dive) * fn2 / (double)N2_IN_AIR), dive);
 		entry->eadd = mbar_to_depth((int)(depth_to_mbarf(entry->depth, dive) *
 				      (entry->pressures.o2 / amb_pressure * O2_DENSITY +
 				       entry->pressures.n2 / amb_pressure * N2_DENSITY +