/**
 * @file     vtime.c
 * @brief    Sample program of VL2 GCSC to LLT conversion
 * @author   Yukio Yamamoto
 * @date     2015-03-24
 */

/*
 * This program is converted from FORTRAN version 'vtimec.f'.
 * http://www.ig.utexas.edu/people/staff/yosio/Viking/Programs/vtimec.f
 */

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

#define SOL_CSEC 8877525

/**
 * @brief gcsc to llt conversion based on algorithm on page V1-143
 *
 * @param[in]  gcsc  GCSC Count
 * @param[in]  doy   Day-Of-Year 1976
 * @param[out] sol   SOL of local lander time
 * @param[out] hour  hours of LLT in SOL
 * @param[out] min   minutes of LLT in SOL
 * @param[out] csec  centiseconds of LLT in SOL 
 */
void gcsc2llt(int gcsc, int doy, int* sol, int* hour, int* min, int* csec) {
    int i, ige;
    double ge16, t, tr;
    const double lo0 = 2344400;
    const int maxg[] = {
        11242789,36555517,67108864,93338597,134217728,201326592,320000000
    };
    const double cg[] = {
        8.4276E-6,8.99984E-6,1.01318E-5,1.81923E-5,1.38394E-5,1.36977E-5,1.47743E-5
    };
    const int lo[] = {
        0,103,765,9420,2919,2614,6082
    };
    
    ige = (doy-232)*540000-gcsc;
    ige &= 0xff000000;
    ige += gcsc;
    for (i=0; i<7; ++i) {
        if (ige <= maxg[i]) {
            break;
        }
    }
    ge16 = ige * 16.0;
    t = (ge16-cg[i]*ge16+lo[i]+lo0)/SOL_CSEC;
    *sol = t;
    tr = (t-*sol)*(SOL_CSEC/360000.0);
    *hour = tr;
    tr = (tr-*hour)*60;
    *min = tr;
    *csec = (tr-*min)*6000+0.5;
}

/*
 * sample main program
 */
int main() {
  int gcsc = 8145579;  /* GCSC example  */
  int doy = 261;       /* Sep. 17, 1976 */
  int sol, hour, min, csec;
  gcsc2llt(gcsc, doy, &sol, &hour, &min, &csec);
  printf("%d %02d:%02d:%02d.%02d\n",
	 sol,hour,min,(int)(csec/100),csec%100);
  return EXIT_SUCCESS;
}