//
// sr -- General Relativity (time dilation) calculator for low elevation.
//
// 30-Apr-2006 tvb www.LeapSecond.com/tools
//

#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define INCH_TO_METER(x) ( (x) * 2.54 / 100.0 )
#define FOOT_TO_METER(x) ( INCH_TO_METER((x) * 12) )

#define ALL_UNITS "ft, m, km"

void main (int argc, char *argv[])
{
    double c = 299792458.0;
    double g = 9.82;
    double height, h, df;
    char *units;

    if (argc < 3) {
        fprintf(stderr, "Usage: %s [height] [units]\n", argv[0]);
        fprintf(stderr, "(height units are one of: %s)\n", ALL_UNITS);
        exit(1);
    }

    height = atof(argv[1]);
    units = argv[2];
    if (strcmp(units, "ft") == 0) {
        h = FOOT_TO_METER(height);
    }
    else if (strcmp(units, "m") == 0) {
        h = height;
    }
    else if (strcmp(units, "km") == 0) {
        h = height * 1000;
    }
    else {
        fprintf(stderr, "Unit %s unknown. Valid units: %s\n", units, ALL_UNITS);
        exit(1);
    }

    if (h < 0) {
        fprintf(stderr, "Height too low for this tool.\n");
        exit(1);
    }

    printf("%16.6lf feet\n", 1/FOOT_TO_METER(1/h));
    printf("%16.6lf km\n", h / 1000);
    printf("%16.6lf m\n", h);
    printf("%16.6lf g\n", g);

    // Stay close to earth.
    if (h > 10000) {
        fprintf(stderr, "Height too high for this tool.\n");
        exit(1);
    }

    df = g * h / (c * c);
    printf("%16.6le g*h/c^2\n", df);
    printf("%16.6lf ps/hour\n", df * 1e12 * 3600);
    printf("%16.6lf ns/day\n", df * 1e9 * 86400);
}