calc unix epoch time froom date using C

calc_epochtime.c

//gcc calc_epochtime.c

#include <stdio.h>
#include <stdint.h>
#include <time.h>

struct tm gtmCurrentTime;

void intoDatetime(uint16_t uiYearAc, uint8_t uiMonthOrg, uint8_t uiDate, uint8_t uiHour, uint8_t uiMinute, uint8_t uiSecond ,struct tm *ptm){
  //usage : intoDatetime( 2022,12,6,17,30,5);
  ptm->tm_year = uiYearAc - 1900;
  ptm->tm_mon = uiMonthOrg -1;
  ptm->tm_mday = uiDate;
  ptm->tm_hour = uiHour;
  ptm->tm_min = uiMinute;
  ptm->tm_sec = uiSecond;
}//intoDatetime


uint32_t calcSumDateMonth(uint8_t uiMonth0){
  uint16_t uiTblMonthSumDate[] = {0,31,59,90,120,151,181,212,243,273,304,334,365};
  return(uiTblMonthSumDate[uiMonth0]);
}//calcSumDateMonth

uint32_t calcTotalDayFrom1970Jan01(uint8_t uiYear1900, uint8_t uiMonth0, uint8_t uiDate){
  uint8_t uiYear = uiYear1900 -70; //from 1970
  uint32_t uiSumDay = uiDate - 1;
  uiSumDay += calcSumDateMonth(uiMonth0);
  uiSumDay += (uiYear>>2) * (365*4+1); // 4year cycle
  uiSumDay += (uiYear&3) * (365);  // remain year in cycle
  uiSumDay += 1 * (uiYear <= 30); // for 1972 to 2000
  uiSumDay += ( ((uiYear+2)&3)==0 )*(uiMonth0 > 2); //leap year from 1972
  return(uiSumDay);
}//calcTotalDayFrom1970Jan01


uint32_t calcTotalSecToday(uint8_t uiHour, uint8_t uiMinute, uint8_t uiSecond){
  uint32_t uiTmSec = uiSecond;
  uiTmSec += uiMinute * 60;
  uiTmSec += uiHour * 3600;
  return(uiTmSec);
}//calcTotalSecToday


uint32_t calcUnixEpochSecondFrom1970Jan01Tm(uint8_t uiYear1900, uint8_t uiMonth0, uint8_t uiDate, uint8_t uiHour, uint8_t uiMinute, uint8_t uiSecond)
{ //usage: res = calcUnixEpochSecondFrom1970Jan01Tm( 2022-1900, 12-1, 6, 17,30,5);
  uint32_t uiSumSec=0;
  uiSumSec += (uint32_t)(3600*24)* calcTotalDayFrom1970Jan01( uiYear1900,  uiMonth0,  uiDate);
  uiSumSec += calcTotalSecToday(uiHour,  uiMinute,  uiSecond);
  return(uiSumSec);
}//calcUnixEpochSecondFrom1970Jan01Tm


uint32_t tm2Epoch(struct tm *ptm){
  uint8_t uiYear1900 = ptm->tm_year;
  uint8_t uiMonth0 = ptm->tm_mon;
  uint8_t uiDate = ptm->tm_mday;
  uint8_t uiHour = ptm->tm_hour;
  uint8_t uiMinute = ptm->tm_min;
  uint8_t uiSecond = ptm->tm_sec;
  return( calcUnixEpochSecondFrom1970Jan01Tm( uiYear1900,  uiMonth0,  uiDate,  uiHour,  uiMinute,  uiSecond));
}//tm2Epoch


void printTime(){
    printf(" ");
    printf("%d",gtmCurrentTime.tm_year+1900);
    printf(" / ");
    printf("%d",gtmCurrentTime.tm_mon+1);
    printf("/");
    printf("%d",gtmCurrentTime.tm_mday);
    printf(" _ ");
    printf("%d",gtmCurrentTime.tm_hour);
    printf(":");
    printf("%d",gtmCurrentTime.tm_min);
    printf(":");
    printf("%d",gtmCurrentTime.tm_sec);
    printf("\n");
}//printTime


int main(){

  intoDatetime(2022,12,6,16,30,5, &gtmCurrentTime);
  printTime();

  printf("tm2Epoch %d\n",tm2Epoch(&gtmCurrentTime));
  printf("calc %d\n", calcUnixEpochSecondFrom1970Jan01Tm(2022-1900,12-1,6,16,30,5));

  return 0;

}


/*

result =  (total Day from epoch) * 3600*24  +  (todaysec )

tm2Epoch(&dt)
 L calcUnixEpochSecondFrom1970Jan01Tm( y,M,d,h,m,s)
   |- calcTotalDayFrom1970Jan01(y,M,d)
   L  calcTotalSecToday(h,m,s)
       L calcSumDateMonth(m)


intoDatetime(2022,12,6,17,30,5, &dt)
 dt ->  
  tm_year = 122 = 2022 -1900
  tm_mon = 11 = 12 - 1
  tm_mday = 6
  tm_hour = 17
  tm_min = 30
  tm_sec = 5

*/