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extern /* Subroutine */ int calc_barometric_pressure();
extern /* Subroutine */ int calc_deco_ceiling();
extern /* Subroutine */ int onset_of_impermeability();
extern /* Subroutine */ int radius_root_finder();
extern /* Subroutine */ int nuclear_regeneration(), clock_();
extern /* Subroutine */ int vpm_repetitive_algorithm();
extern /* Subroutine */ int gas_loadings_surface_interval();
extern /* Subroutine */ int critical_volume();	    ;
extern /* Subroutine */ int calc_crushing_pressure(), 
                            calc_surface_phase_volume_time(), 
                            decompression_stop();
extern /* Subroutine */ int calc_start_of_deco_zone();
extern /* Subroutine */ int calc_initial_allowable_gradient(), 
                            gas_loadings_ascent_descen();
extern /* Subroutine */ int gas_loadings_constant_depth();
extern /* Subroutine */ int vpm_altitude_dive_algorithm();
extern /* Subroutine */ int calc_max_actual_gradient(), 
                            projected_ascent();

extern /* Subroutine */ doublereal schreiner_equation__();
extern /* Subroutine */ doublereal haldane_equation__();

/* =============================================================================== */
/*     SUBROUTINE CALC_BAROMETRIC_PRESSURE */
/*     Purpose: This sub calculates barometric pressure at altitude based on the */
/*     publication "U.S. Standard Atmosphere, 1976", U.S. Government Printing */
/*     Office, Washington, D.C. The source for this code is a Fortran 90 program */
/*     written by Ralph L. Carmichael (retired NASA researcher) and endorsed by */
/*     the National Geophysical Data Center of the National Oceanic and */
/*     Atmospheric Administration.  It is available for download free from */
/*     Public Domain Aeronautical Software at:  http://www.pdas.com/atmos.htm */
/* =============================================================================== */

int calc_barometric_pressure(real *altitude)
{
    /* Local variables */
    static real altitude_meters, 
                molecular_weight_of_air, 
	            acceleration_of_operation, 
                altitude_kilometers, 
                altitude_feet,
	            temp_gradient, 
                temp_at_sea_level, 
                pressure_at_sea_level, 
	            geopotential_altitude, 
                gmr_factor, 
	            pressure_at_sea_level_fsw, 
                pressure_at_sea_level_msw, 
	            temp_at_geopotential_altitude, 
                gas_constant_r, 
	            radius_of_earth;

/* =============================================================================== */
/*     CALCULATIONS */
/* =============================================================================== */

    radius_of_earth = 6369.;                 /* ki */
    acceleration_of_operation = 9.80665;     /* meters/ */
    molecular_weight_of_air = 28.9644;
    gas_constant_r = 8.31432;                /* Joules/mol*de */
    temp_at_sea_level = 288.15;              /* degree */
    pressure_at_sea_level_fsw = 33.;         /* at sea level (Standard Atm */
                                             /* feet of seawater based on 1 */
    pressure_at_sea_level_msw = 10.;         /* at sea level (European */
                                             /* meters of seawater based on 1 */
    temp_gradient = -6.5;                    /* change in geopotential a */
                                             /* valid for first layer of at */
                                             /* up to 11 kilometers or 36, */
                                             /* Change in Temp deg Kel */
    gmr_factor = 
        acceleration_of_operation * molecular_weight_of_air / gas_constant_r;
    if (units_equal_fsw) {
	    altitude_feet = *altitude;
	    altitude_kilometers = altitude_feet / 3280.839895;
	    pressure_at_sea_level = pressure_at_sea_level_fsw;
    }
    if (units_equal_msw) {
	    altitude_meters = *altitude;
	    altitude_kilometers = altitude_meters / 1e3;
	    pressure_at_sea_level = pressure_at_sea_level_msw;
    }
    geopotential_altitude = 
        altitude_kilometers * radius_of_earth / (altitude_kilometers + radius_of_earth);
    temp_at_geopotential_altitude = 
        temp_at_sea_level + temp_gradient * geopotential_altitude;
    barometric_pressure = 
        pressure_at_sea_level * 
        exp(log(temp_at_sea_level / temp_at_geopotential_altitude) * gmr_factor / temp_gradient);

    return 0;
} /* calc_barometric_pressure */

/* =============================================================================== */
/*     SUBROUTINE CALC_DECO_CEILING */
/*     Purpose: This subprogram calculates the deco ceiling (the safe ascent */
/*     depth) in each compartment, based on the allowable gradients, and then */
/*     finds the deepest deco ceiling across all compartments.  This deepest */
/*     value (Deco Ceiling Depth) is then used by the Decompression Stop */
/*     subroutine to determine the actual deco schedule. */
/* =============================================================================== */

int calc_deco_ceiling(real *deco_ceiling_depth)
{
    /* System generated locals */
    real r1, r2;

    /* Local variables */
    static real weighted_allowable_gradient;
    static integer i;
    static real compartment_deco_ceiling[16], 
                gas_loading, 
	            tolerated_ambient_pressure;

/* loop */
/* =============================================================================== */
/*     CALCULATIONS */
/*     Since there are two sets of allowable gradients being tracked, one for */
/*     helium and one for nitrogen, a "weighted allowable gradient" must be */
/*     computed each time based on the proportions of helium and nitrogen in */
/*     each compartment.  This proportioning follows the methodology of */
/*     Buhlmann/Keller.  If there is no helium and nitrogen in the compartment, */
/*     such as after extended periods of oxygen breathing, then the minimum value */
/*     across both gases will be used.  It is important to note that if a */
/*     compartment is empty of helium and nitrogen, then the weighted allowable */
/*     gradient formula cannot be used since it will result in division by zero. */
/* =============================================================================== */

    for (i = 1; i <= 16; ++i) {
	    gas_loading = 
            helium_pressure[i - 1] + nitrogen_pressure[i - 1];
	    if (gas_loading > 0.) {
	        weighted_allowable_gradient = 
		        (allowable_gradient_he[i - 1] * helium_pressure[i - 1] + 
		            allowable_gradient_n2[i - 1] * nitrogen_pressure[i - 1]) / 
		                (helium_pressure[i - 1] + nitrogen_pressure[i - 1]);
	        tolerated_ambient_pressure = 
                gas_loading + 
		        constant_pressure_other_gases - 
		        weighted_allowable_gradient;
	    } else {
            /* Computing MIN */
	        r1 = allowable_gradient_he[i - 1];
            r2 = allowable_gradient_n2[i - 1];
	        weighted_allowable_gradient = min(r1,r2);
	        tolerated_ambient_pressure = 
		        constant_pressure_other_gases - weighted_allowable_gradient;
	    }

/* =============================================================================== */
/*     The tolerated ambient pressure cannot be less than zero absolute, i.e., */
/*     the vacuum of outer space! */
/* =============================================================================== */

	    if (tolerated_ambient_pressure < 0.) {
	        tolerated_ambient_pressure = 0.;
	    }
	    compartment_deco_ceiling[i - 1] = 
            tolerated_ambient_pressure - barometric_pressure;
    }

/* =============================================================================== */
/*     The Deco Ceiling Depth is computed in a loop after all of the individual */
/*     compartment deco ceilings have been calculated.  It is important that the */
/*     Deco Ceiling Depth (max deco ceiling across all compartments) only be */
/*     extracted from the compartment values and not be compared against some */
/*     initialization value.  For example, if MAX(Deco_Ceiling_Depth . .) was */
/*     compared against zero, this could cause a program lockup because sometimes */
/*     the Deco Ceiling Depth needs to be negative (but not less than zero */
/*     absolute ambient pressure) in order to decompress to the last stop at zero */
/*     depth. */
/* =============================================================================== */

    *deco_ceiling_depth = compartment_deco_ceiling[0];
    for (i = 2; i <= 16; ++i) {
        /* Computing MAX */
	    r1 = *deco_ceiling_depth;
        r2 = compartment_deco_ceiling[i - 1];
	    *deco_ceiling_depth = max(r1,r2);
    }
    return 0;
} /* calc_deco_ceiling */