已经有注解，还有算法，会C51的一看就会用的了
#define uchar unsigned char
#define uint unsigned int
＃i nclude "reg51.h"

// By Campo
code uchar year_code[597]={
   0x04,0xAe,0x53,   //1901 0
   0x0A,0x57,0x48,     //1902 3
   0x55,0x26,0xBd,  //1903 6
   0x0d,0x26,0x50,  //1904 9
   0x0d,0x95,0x44,     //1905 12
   0x46,0xAA,0xB9,  //1906 15
   0x05,0x6A,0x4d,  //1907 18
   0x09,0xAd,0x42,  //1908 21
   0x24,0xAe,0xB6,  //1909
   0x04,0xAe,0x4A,  //1910
   0x6A,0x4d,0xBe,  //1911
   0x0A,0x4d,0x52,  //1912
   0x0d,0x25,0x46,  //1913
   0x5d,0x52,0xBA,  //1914
   0x0B,0x54,0x4e,  //1915
   0x0d,0x6A,0x43,  //1916
   0x29,0x6d,0x37,  //1917
   0x09,0x5B,0x4B,  //1918
   0x74,0x9B,0xC1,  //1919
   0x04,0x97,0x54,  //1920
   0x0A,0x4B,0x48,  //1921
   0x5B,0x25,0xBC,  //1922
   0x06,0xA5,0x50,  //1923
   0x06,0xd4,0x45,  //1924
   0x4A,0xdA,0xB8,  //1925
   0x02,0xB6,0x4d,  //1926
   0x09,0x57,0x42,  //1927
   0x24,0x97,0xB7,  //1928
   0x04,0x97,0x4A,  //1929
   0x66,0x4B,0x3e,  //1930
   0x0d,0x4A,0x51,  //1931
   0x0e,0xA5,0x46,  //1932
   0x56,0xd4,0xBA,  //1933
   0x05,0xAd,0x4e,  //1934
   0x02,0xB6,0x44,  //1935
   0x39,0x37,0x38,  //1936
   0x09,0x2e,0x4B,  //1937
   0x7C,0x96,0xBf,  //1938
   0x0C,0x95,0x53,  //1939
   0x0d,0x4A,0x48,  //1940
   0x6d,0xA5,0x3B,  //1941
   0x0B,0x55,0x4f,  //1942
   0x05,0x6A,0x45,  //1943
   0x4A,0xAd,0xB9,  //1944
   0x02,0x5d,0x4d,  //1945
   0x09,0x2d,0x42,  //1946
   0x2C,0x95,0xB6,  //1947
   0x0A,0x95,0x4A,  //1948
   0x7B,0x4A,0xBd,  //1949
   0x06,0xCA,0x51,  //1950
   0x0B,0x55,0x46,  //1951
   0x55,0x5A,0xBB,  //1952
   0x04,0xdA,0x4e,  //1953
   0x0A,0x5B,0x43,  //1954
   0x35,0x2B,0xB8,  //1955
   0x05,0x2B,0x4C,  //1956
   0x8A,0x95,0x3f,  //1957
   0x0e,0x95,0x52,  //1958
   0x06,0xAA,0x48,  //1959
   0x7A,0xd5,0x3C,  //1960
   0x0A,0xB5,0x4f,  //1961
   0x04,0xB6,0x45,  //1962
   0x4A,0x57,0x39,  //1963
   0x0A,0x57,0x4d,  //1964
   0x05,0x26,0x42,  //1965
   0x3e,0x93,0x35,  //1966
   0x0d,0x95,0x49,  //1967
   0x75,0xAA,0xBe,  //1968
   0x05,0x6A,0x51,  //1969
   0x09,0x6d,0x46,  //1970
   0x54,0xAe,0xBB,  //1971
   0x04,0xAd,0x4f,  //1972
   0x0A,0x4d,0x43,  //1973
   0x4d,0x26,0xB7,  //1974
   0x0d,0x25,0x4B,  //1975
   0x8d,0x52,0xBf,  //1976
   0x0B,0x54,0x52,  //1977
   0x0B,0x6A,0x47,  //1978
   0x69,0x6d,0x3C,  //1979
   0x09,0x5B,0x50,  //1980
   0x04,0x9B,0x45,  //1981
   0x4A,0x4B,0xB9,  //1982
   0x0A,0x4B,0x4d,  //1983
   0xAB,0x25,0xC2,  //1984
   0x06,0xA5,0x54,  //1985
   0x06,0xd4,0x49,  //1986
   0x6A,0xdA,0x3d,  //1987
   0x0A,0xB6,0x51,  //1988
   0x09,0x37,0x46,  //1989
   0x54,0x97,0xBB,  //1990
   0x04,0x97,0x4f,  //1991
   0x06,0x4B,0x44,  //1992
   0x36,0xA5,0x37,  //1993
   0x0e,0xA5,0x4A,  //1994
   0x86,0xB2,0xBf,  //1995
   0x05,0xAC,0x53,  //1996
   0x0A,0xB6,0x47,  //1997
   0x59,0x36,0xBC,  //1998
   0x09,0x2e,0x50,  //1999 294
   0x0C,0x96,0x45,  //2000 297
   0x4d,0x4A,0xB8,  //2001
   0x0d,0x4A,0x4C,  //2002
   0x0d,0xA5,0x41,  //2003
   0x25,0xAA,0xB6,  //2004
   0x05,0x6A,0x49,  //2005
   0x7A,0xAd,0xBd,  //2006
   0x02,0x5d,0x52,  //2007
   0x09,0x2d,0x47,  //2008
   0x5C,0x95,0xBA,  //2009
   0x0A,0x95,0x4e,  //2010
   0x0B,0x4A,0x43,  //2011
   0x4B,0x55,0x37,  //2012
   0x0A,0xd5,0x4A,  //2013
   0x95,0x5A,0xBf,  //2014
   0x04,0xBA,0x53,  //2015
   0x0A,0x5B,0x48,  //2016
   0x65,0x2B,0xBC,  //2017
   0x05,0x2B,0x50,  //2018
   0x0A,0x93,0x45,  //2019
   0x47,0x4A,0xB9,  //2020
   0x06,0xAA,0x4C,  //2021
   0x0A,0xd5,0x41,  //2022
   0x24,0xdA,0xB6,  //2023
   0x04,0xB6,0x4A,  //2024
   0x69,0x57,0x3d,  //2025
   0x0A,0x4e,0x51,  //2026
   0x0d,0x26,0x46,  //2027
   0x5e,0x93,0x3A,  //2028
   0x0d,0x53,0x4d,  //2029
   0x05,0xAA,0x43,  //2030
   0x36,0xB5,0x37,  //2031
   0x09,0x6d,0x4B,  //2032
   0xB4,0xAe,0xBf,  //2033
   0x04,0xAd,0x53,  //2034
   0x0A,0x4d,0x48,  //2035
   0x6d,0x25,0xBC,  //2036
   0x0d,0x25,0x4f,  //2037
   0x0d,0x52,0x44,  //2038
   0x5d,0xAA,0x38,  //2039
   0x0B,0x5A,0x4C,  //2040
   0x05,0x6d,0x41,  //2041
   0x24,0xAd,0xB6,  //2042
   0x04,0x9B,0x4A,  //2043
   0x7A,0x4B,0xBe,  //2044
   0x0A,0x4B,0x51,  //2045
   0x0A,0xA5,0x46,  //2046
   0x5B,0x52,0xBA,  //2047
   0x06,0xd2,0x4e,  //2048
   0x0A,0xdA,0x42,  //2049
   0x35,0x5B,0x37,  //2050
   0x09,0x37,0x4B,  //2051
   0x84,0x97,0xC1,  //2052
   0x04,0x97,0x53,  //2053
   0x06,0x4B,0x48,  //2054
   0x66,0xA5,0x3C,  //2055
   0x0e,0xA5,0x4f,  //2056
   0x06,0xB2,0x44,  //2057
   0x4A,0xB6,0x38,  //2058
   0x0A,0xAe,0x4C,  //2059
   0x09,0x2e,0x42,  //2060
   0x3C,0x97,0x35,  //2061
   0x0C,0x96,0x49,  //2062
   0x7d,0x4A,0xBd,  //2063
   0x0d,0x4A,0x51,  //2064
   0x0d,0xA5,0x45,  //2065
   0x55,0xAA,0xBA,  //2066
   0x05,0x6A,0x4e,  //2067
   0x0A,0x6d,0x43,  //2068
   0x45,0x2e,0xB7,  //2069
   0x05,0x2d,0x4B,  //2070
   0x8A,0x95,0xBf,  //2071
   0x0A,0x95,0x53,  //2072
   0x0B,0x4A,0x47,  //2073
   0x6B,0x55,0x3B,  //2074
   0x0A,0xd5,0x4f,  //2075
   0x05,0x5A,0x45,  //2076
   0x4A,0x5d,0x38,  //2077
   0x0A,0x5B,0x4C,  //2078
   0x05,0x2B,0x42,  //2079
   0x3A,0x93,0xB6,  //2080
   0x06,0x93,0x49,  //2081
   0x77,0x29,0xBd,  //2082
   0x06,0xAA,0x51,  //2083
   0x0A,0xd5,0x46,  //2084
   0x54,0xdA,0xBA,  //2085
   0x04,0xB6,0x4e,  //2086
   0x0A,0x57,0x43,  //2087
   0x45,0x27,0x38,  //2088
   0x0d,0x26,0x4A,  //2089
   0x8e,0x93,0x3e,  //2090
   0x0d,0x52,0x52,  //2091
   0x0d,0xAA,0x47,  //2092
   0x66,0xB5,0x3B,  //2093
   0x05,0x6d,0x4f,  //2094
   0x04,0xAe,0x45,  //2095
   0x4A,0x4e,0xB9,  //2096
   0x0A,0x4d,0x4C,  //2097
   0x0d,0x15,0x41,  //2098
   0x2d,0x92,0xB5,  //2099
};

code uchar
day_code1[9]={0x0,0x1f,0x3b,0x5a,0x78,0x97,0xb5,0xd4,0xf3};
code uint day_code2[3]={0x111,0x130,0x14e};

bit c_moon;
data uchar year_moon,month_moon,day_moon,week;

bit get_moon_day(uchar month_p,uint table_addr){
 switch (month_p){
  case
1:{if((year_code[table_addr]&0x08)==0)return(0);else
return(1);}
  case
2:{if((year_code[table_addr]&0x04)==0)return(0);else
return(1);}
  case
3:{if((year_code[table_addr]&0x02)==0)return(0);else
return(1);}
  case
4:{if((year_code[table_addr]&0x01)==0)return(0);else
return(1);}
  case
5:{if((year_code[table_addr+1]&0x80)==0)return(0);else
return(1);}
  case
6:{if((year_code[table_addr+1]&0x40)==0)return(0);else
return(1);}
  case
7:{if((year_code[table_addr+1]&0x20)==0)return(0);else
return(1);}
  case
8:{if((year_code[table_addr+1]&0x10)==0)return(0);else
return(1);}
  case
9:{if((year_code[table_addr+1]&0x08)==0)return(0);else
return(1);}
  case
10:{if((year_code[table_addr+1]&0x04)==0)return(0);else
return(1);}
  case
11:{if((year_code[table_addr+1]&0x02)==0)return(0);else
return(1);}
  case
12:{if((year_code[table_addr+1]&0x01)==0)return(0);else
return(1);}
  case
13:{if((year_code[table_addr+2]&0x80)==0)return(0);else
return(1);}
 }
}

void Conversion(bit c,uchar year,uchar month,uchar day){
 //c=0 为21世纪,c=1 为19世纪 输入输出数据均为BCD数据
 uchar temp1,temp2,temp3,month_p;
 uint temp4,table_addr;
 bit flag_y;
 //BCD->hex 先把数据转换为十六进制
 year=year/16*10+year;
 
 month=month/16*10+month;
 day=day/16*10+day;
 //定位数据表地址
 if(c==0){                  
  table_addr=(year+0x64-1)*0x3;
 }
 else {
  table_addr=(year-1)*0x3;
 }
 //定位数据表地址完成
 //取当年春节所在的公历月份
 temp1=year_code[table_addr+2]&0x60;
 temp1=_cror_(temp1,5);
 //取当年春节所在的公历月份完成
 //取当年春节所在的公历日
 temp2=year_code[table_addr+2]&0x1f;
 //取当年春节所在的公历日完成
 // 计算当年春年离当年元旦的天数,春节只会在公历1月或2月
 if(temp1==0x1){ 
  temp3=temp2-1; 
 } 
 else{
  temp3=temp2+0x1f-1; 
 }
 // 计算当年春年离当年元旦的天数完成
 //计算公历日离当年元旦的天数,为了减少运算,用了两个表day_code1[9],day_code2[3]
 
//如果公历月在九月或前,天数会少于0xff,用表day_code1[9],在九月后,天数大于0xff,用表day_code2[3]
 //如输入公历日为8月10日,则公历日离元旦天数为day_code1[8-1]+10-1
 //如输入公历日为11月10日,则公历日离元旦天数为day_code2[11-10]+10-1
 if (month<10){
  temp4=day_code1[month-1]+day-1;
 }
 else{
  temp4=day_code2[month-10]+day-1;
 }
 if ((month>0x2)&&(year%0x4==0)){ 
//如果公历月大于2月并且该年的2月为闰月,天数加1
  temp4+=1;
 }
 //计算公历日离当年元旦的天数完成
 //判断公历日在春节前还是春节后
 if (temp4>=temp3){ //公历日在春节后或就是春节当日使用下面代码进行运算
  temp4-=temp3;
  month=0x1;
  month_p=0x1;  //month_p为月份指向,公历日在春节前或就是春节当日month_p指向首月
   //检查该农历月为大小还是小月,大月返回1,小月返回0
  flag_y=0;
  if(get_moon_day(month_p,table_addr)==0)temp1=0x1d;
//小月29天
  else temp1=0x1e; //大小30天
  temp2=year_code[table_addr]/16; 
//从数据表中取该年的闰月月份,如为0则该年无闰月
 
//效果和temp2=year_code[table_addr]&0xf0;temp2=_cror_(temp2,4)一样,但生成代码更简洁
  while(temp4>=temp1){
   temp4-=temp1;
   month_p+=1;
   if(month==temp2){
   flag_y=~flag_y;
   if(flag_y==0)month+=1;
   }
   else month+=1;
   if(get_moon_day(month_p,table_addr)==0)temp1=0x1d;
   else temp1=0x1e;
  }
  day=temp4+1;
 }
 else{  //公历日在春节前使用下面代码进行运算
     temp3-=temp4;
  if (year==0x0){year=0x63;c=1;}
  else year-=1;
  table_addr-=0x3;
  month=0xc;
  temp2=year_code[table_addr]/16;
  if (temp2==0)month_p=0xc;
  else month_p=0xd;
 
  flag_y=0;
  if(get_moon_day(month_p,table_addr)==0)temp1=0x1d;
  else temp1=0x1e;
  while(temp3>temp1){
   temp3-=temp1;
   month_p-=1;
   if(flag_y==0)month-=1;
   if(month==temp2)flag_y=~flag_y;
   if(get_moon_day(month_p,table_addr)==0)temp1=0x1d;
   else temp1=0x1e;
   }
  day=temp1-temp3+1;
 }
 c_moon=c;                 //HEX->BCD ,运算结束后,把数据转换为BCD数据
 year_moon=(year/10*16)|(year);
 
 month_moon=(month/10*16)|(month);
 day_moon=(day/10*16)|(day);
}

code uchar table_week[12]={0,3,3,6,1,4,6,2,5,0,3,5};
//月修正数据表

void Conver_week(bit c,uchar year,uchar month,uchar
day){//c=0 为21世纪,c=1 为19世纪 输入输出数据均为BCD数据
 uchar temp2;
 //BCD->hex 先把数据转换为十六进制
 year=year/16*10+year;
 month=month/16*10+month;
 day=day/16*10+day;
 if (c==0){year+=0x64;}  //如果为21世纪,年份数加100
  //所过闰年数只算1900年之后的
 temp2=year+year/0x4;
 temp2=temp2%0x7;  //为节省资源,先进行一次取余,避免数大于0xff,避免使用整型数据
 temp2=temp2+day+table_week[month-1];
 if (year%0x4==0&&month<3)temp2-=1;
 week=temp2%0x7;
}
// By Campo