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// SPDX-License-Identifier: GPL-2.0
#include "gas.h"
#include "pref.h"
#include <stdio.h>
#include <string.h>
/* Perform isobaric counterdiffusion calculations for gas changes in trimix dives.
* Here we use the rule-of-fifths where, during a change involving trimix gas, the increase in nitrogen
* should not exceed one fifth of the decrease in helium.
* Parameters: 1) pointers to two gas mixes, the gas being switched from and the gas being switched to.
* 2) a pointer to an icd_data structure.
* Output: i) The icd_data stucture is filled with the delta_N2 and delta_He numbers (as permille).
* ii) Function returns a boolean indicating an exceeding of the rule-of-fifths. False = no icd problem.
*/
bool isobaric_counterdiffusion(struct gasmix oldgasmix, struct gasmix newgasmix, struct icd_data *results)
{
if (!prefs.show_icd)
return false;
results->dN2 = get_n2(newgasmix) - get_n2(oldgasmix);
results->dHe = get_he(newgasmix) - get_he(oldgasmix);
return get_he(oldgasmix) > 0 && results->dN2 > 0 && results->dHe < 0 && get_he(oldgasmix) && results->dN2 > 0 && 5 * results->dN2 > -results->dHe;
}
static bool gasmix_is_invalid(struct gasmix mix)
{
return mix.o2.permille < 0;
}
int same_gasmix(struct gasmix a, struct gasmix b)
{
if (gasmix_is_invalid(a) || gasmix_is_invalid(b))
return 0;
if (gasmix_is_air(a) && gasmix_is_air(b))
return 1;
return a.o2.permille == b.o2.permille && a.he.permille == b.he.permille;
}
void sanitize_gasmix(struct gasmix *mix)
{
unsigned int o2, he;
o2 = mix->o2.permille;
he = mix->he.permille;
/* Regular air: leave empty */
if (!he) {
if (!o2)
return;
/* 20.8% to 21% O2 is just air */
if (gasmix_is_air(*mix)) {
mix->o2.permille = 0;
return;
}
}
/* Sane mix? */
if (o2 <= 1000 && he <= 1000 && o2 + he <= 1000)
return;
fprintf(stderr, "Odd gasmix: %u O2 %u He\n", o2, he);
memset(mix, 0, sizeof(*mix));
}
int gasmix_distance(struct gasmix a, struct gasmix b)
{
int a_o2 = get_o2(a), b_o2 = get_o2(b);
int a_he = get_he(a), b_he = get_he(b);
int delta_o2 = a_o2 - b_o2, delta_he = a_he - b_he;
delta_he = delta_he * delta_he;
delta_o2 = delta_o2 * delta_o2;
return delta_he + delta_o2;
}
bool gasmix_is_air(struct gasmix gasmix)
{
int o2 = gasmix.o2.permille;
int he = gasmix.he.permille;
return (he == 0) && (o2 == 0 || ((o2 >= O2_IN_AIR - 1) && (o2 <= O2_IN_AIR + 1)));
}
static fraction_t make_fraction(int i)
{
fraction_t res;
res.permille = i;
return res;
}
fraction_t get_gas_component_fraction(struct gasmix mix, enum gas_component component)
{
switch (component) {
case O2: return make_fraction(get_o2(mix));
case N2: return make_fraction(get_n2(mix));
case HE: return make_fraction(get_he(mix));
default: return make_fraction(0);
}
}
/* fill_pressures(): Compute partial gas pressures in bar from gasmix and ambient pressures, possibly for OC or CCR, to be
* extended to PSCT. This function does the calculations of gas pressures applicable to a single point on the dive profile.
* The structure "pressures" is used to return calculated gas pressures to the calling software.
* Call parameters: po2 = po2 value applicable to the record in calling function
* amb_pressure = ambient pressure applicable to the record in calling function
* *pressures = structure for communicating o2 sensor values from and gas pressures to the calling function.
* *mix = structure containing cylinder gas mixture information.
* divemode = the dive mode pertaining to this point in the dive profile.
* This function called by: calculate_gas_information_new() in profile.c; add_segment() in deco.c.
*/
void fill_pressures(struct gas_pressures *pressures, const double amb_pressure, struct gasmix mix, double po2, enum divemode_t divemode)
{
if ((divemode != OC) && po2) { // This is a rebreather dive where pressures->o2 is defined
if (po2 >= amb_pressure) {
pressures->o2 = amb_pressure;
pressures->n2 = pressures->he = 0.0;
} else {
pressures->o2 = po2;
if (get_o2(mix) == 1000) {
pressures->he = pressures->n2 = 0;
} else {
pressures->he = (amb_pressure - pressures->o2) * (double)get_he(mix) / (1000 - get_o2(mix));
pressures->n2 = amb_pressure - pressures->o2 - pressures->he;
}
}
} else {
if (divemode == PSCR) { /* The steady state approximation should be good enough */
pressures->o2 = get_o2(mix) / 1000.0 * amb_pressure - (1.0 - get_o2(mix) / 1000.0) * prefs.o2consumption / (prefs.bottomsac * prefs.pscr_ratio / 1000.0);
if (pressures->o2 < 0) // He's dead, Jim.
pressures->o2 = 0;
if (get_o2(mix) != 1000) {
pressures->he = (amb_pressure - pressures->o2) * get_he(mix) / (1000.0 - get_o2(mix));
pressures->n2 = (amb_pressure - pressures->o2) * get_n2(mix) / (1000.0 - get_o2(mix));
} else {
pressures->he = pressures->n2 = 0;
}
} else {
// Open circuit dives: no gas pressure values available, they need to be calculated
pressures->o2 = get_o2(mix) / 1000.0 * amb_pressure; // These calculations are also used if the CCR calculation above..
pressures->he = get_he(mix) / 1000.0 * amb_pressure; // ..returned a po2 of zero (i.e. o2 sensor data not resolvable)
pressures->n2 = get_n2(mix) / 1000.0 * amb_pressure;
}
}
}
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