Workingdays - Calculate the number of business days in a given year

workingdays.c

// Workingdays - Calculate the number of business days in a given year
// Copyright (c) 2014 Max Weller

// COMPILE AND RUN:
// $ gcc -o workingdays workingdays.c
// $ ./workingdays -h

// Tested with Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn) (x86_64-apple-darwin13.1.0)
// and gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5) (x86_64-linux-gnu)

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

// definition of months
#define JAN 0x0
#define FEB 0x1
#define MAR 0x2
#define APR 0x3
#define MAY 0x4
#define JUN 0x5
#define JUL 0x6
#define AUG 0x7
#define SEP 0x8
#define OCT 0x9
#define NOV 0xa
#define DEC 0xb

#define TMOBJ struct tm*
#define DAYSOFYEAR 365

#define IFDAY(myday,d,m) if ((myday->tm_mon == m) && (myday->tm_mday == d))
#define HOLYDAY(d,m,f,n) IFDAY(myday,d,m) MAKEHOLY(d,m,f,n)
#define EASTERDAY(since,f,n) if (march == since) MAKEHOLY(myday->tm_mday,myday->tm_mon,f,n)

#define MAKEHOLY(d,m,f,n) { work[day] = f; if(debug)printf("%02d.%02d.\t%s\n", d, 1+m, n); }

int debug = 0;

float sumdays();
void checkdays(int year);
TMOBJ makemyday(int year, int month, int day);
void nextday(TMOBJ day);
int easter(int X);
int urlaubdays(int year, int start, int jahres);

float work[DAYSOFYEAR];

// format a day of year
char* prnday(int y, int dayofj) {
  return asctime(makemyday(y-1900, 0, dayofj));
}

// main entry point
int main(int argc, char** argv) {
  time_t t = time(NULL);
  TMOBJ now = localtime(&t);
  int year = 0;
  int ju = -1;
  // parse opts
  if (argc == 1) year = now->tm_year + 1900;
  else if (argc == 2 && strcmp(argv[1], "-c") == 0) { year = now->tm_year + 1900; debug = 1; }
  else if (argc == 2) year = atoi(argv[1]);
  else if (argc == 3 && strcmp(argv[1], "-c") == 0) { year = atoi(argv[2]); debug = 1; }
  else if (argc == 4 && strcmp(argv[1], "-j") == 0) { year = atoi(argv[2]); ju = atoi(argv[3]); }
  
  // show usage
  if (year == 0) {
    printf("Usage: %1$s [-c] [year]\n\
   or  %1$s -j year annualVacationDays\n\n\
         -c  display holiday dates and names\n\
         -j  calculate maximum free time\n", argv[0]);
    return 1;
  }
  
  // run calculation
  checkdays(year);
  printf("%f\n", sumdays());
  
  if (ju > -1) {
    int maxu = 0, maxi = 0, i, u;
    for(i = 0; i <= DAYSOFYEAR - ju; i++) {
      u = urlaubdays(year, i, ju);
      if (u > maxu) { maxu = u; maxi = i; }
    }
    printf("You get the maximum free time of %d days if you start your vacation on %s", maxu, prnday(year, maxi+1));
  }
  return 0;
}

// count the holidays
float sumdays() {
  float sum = 0.0; int i;
  for(i = 0; i <= DAYSOFYEAR; i++) sum += work[i];
  return sum;
}

// go through year and check holidays
void checkdays(int year) {
  int e = easter(year);
  year -= 1900;
  TMOBJ myday = makemyday(year, 0, 1);
  int day = 0, march = 0;
  while(myday->tm_year == year) {
    if (myday->tm_mon >= MAR) march++;
    work[day] = 1.0;
    if (myday->tm_wday < 2) work[day] = 0.0;
    
    // definition of fixed holidays
    //        day  month   work    holiday name
    HOLYDAY(    1, JAN,    0.0,    "Neujahr");
    HOLYDAY(    1, MAY,    0.0,    "Maifeiertag");
    HOLYDAY(    3, OCT,    0.0,    "Tag der Deutschen Einheit");
    HOLYDAY(   24, DEC,    0.5,    "Heiligabend");
    HOLYDAY(   25, DEC,    0.0,    "1. Weihnachtsfeiertag");
    HOLYDAY(   26, DEC,    0.0,    "2. Weihnachtsfeiertag");
    
    // definition of movable holidays dependent on easter sunday
    //           delta     work    holiday name
    EASTERDAY(   e - 2,    0.5,    "Karfreitag");
    EASTERDAY(   e + 1,    0.0,    "Ostermontag");
    EASTERDAY(   e + 39,   0.0,    "Christi Himmerfahrt");
    EASTERDAY(   e + 50,   0.0,    "Pfingstmontag");
    
    nextday(myday); day++;
  }
}

// return a pointer to a time structure with the given date
TMOBJ makemyday(int year, int month, int day) {
  time_t t = time(NULL);
  TMOBJ now = localtime(&t);
  now->tm_mon = month; now->tm_mday = day; now->tm_year = year;
  now->tm_hour = 1; now->tm_min = 0; now->tm_sec = 0;
  t = mktime(now);
  TMOBJ first = localtime(&t);
  return first;
}

// increment a time structure by one day
void nextday(TMOBJ day) {
  day->tm_mday++;
  time_t mytime = mktime(day);
  day = localtime(&mytime);
}

// calculate easter day according to the Gaussian formula
int easter(int X) {
  int  K = X / 100;
  int  M = 15 + (3 * K + 3) / 4 - (8 * K + 13) / 25;
  int  S = 2 - (3 * K + 3) / 4;
  int  A = X % 19;
  int  D = (19 * A + M) % 30;
  int  R = (D + A / 11) / 29;
  int OG = 21 + D - R;
  int SZ = 7 - (X + X / 4 + S) % 7;
  int OE = 7 - (OG - SZ) % 7;
  int OS = OG + OE;
  return OS;
}

int urlaubdays(int year, int start, int jahres) {
  int i; float j = jahres;
  for(i = start; i <= DAYSOFYEAR && j > 0; i++) {
    j -= work[i];
  }
  return i - start;
}