1900 2100 年农历公历相互转换算法

在构造日期控件时， 经常需要用到农历和公历的互换对应。 但是网上多是公历对农历的转换，农历到公历的转换较少。并且用到的农历的查表并不统一。 Net中有方便的ChineseCalendar可以计算，但是没有这个的平台就只有自己写了。

转换原理

我们会已知一个从1901年开始 持续200年的，中国农历的日期表，包括每一年的每个月份的大小，闰月的位置，闰月的天数。

当从公历转换为农历时，就需要计算目标日期到1900年春节的天数差，然后在1900年春节的基础上开始做加法，加的日期等于天数差时，这次就可以知道目标日期的农历日期。进位都需要依照找到的表进行计算。

同理，当农历转换为公历时，先计算出目标日期到1900年春节的天数差，然后在1900年春节的基础上加上这些天数，就可以得到公里上的日期。

 

表

        农历月份大小压缩表，两个字节表示一年。两个字节共十六个二进制位数，
        前四个位数表示闰月月份，后十二个位数表示十二个农历月份的大小。
        private static int[] chineseMonths = { 
           0x00,0x04,0xad,0x08,0x5a,0x01,0xd5,0x54,0xb4,0x09,0x64,0x05,0x59,0x45,
           0x95,0x0a,0xa6,0x04,0x55,0x24,0xad,0x08,0x5a,0x62,0xda,0x04,0xb4,0x05,
           0xb4,0x55,0x52,0x0d,0x94,0x0a,0x4a,0x2a,0x56,0x02,0x6d,0x71,0x6d,0x01,
           0xda,0x02,0xd2,0x52,0xa9,0x05,0x49,0x0d,0x2a,0x45,0x2b,0x09,0x56,0x01,
           0xb5,0x20,0x6d,0x01,0x59,0x69,0xd4,0x0a,0xa8,0x05,0xa9,0x56,0xa5,0x04,
           0x2b,0x09,0x9e,0x38,0xb6,0x08,0xec,0x74,0x6c,0x05,0xd4,0x0a,0xe4,0x6a,
           0x52,0x05,0x95,0x0a,0x5a,0x42,0x5b,0x04,0xb6,0x04,0xb4,0x22,0x6a,0x05,
           0x52,0x75,0xc9,0x0a,0x52,0x05,0x35,0x55,0x4d,0x0a,0x5a,0x02,0x5d,0x31,
           0xb5,0x02,0x6a,0x8a,0x68,0x05,0xa9,0x0a,0x8a,0x6a,0x2a,0x05,0x2d,0x09,
           0xaa,0x48,0x5a,0x01,0xb5,0x09,0xb0,0x39,0x64,0x05,0x25,0x75,0x95,0x0a,
           0x96,0x04,0x4d,0x54,0xad,0x04,0xda,0x04,0xd4,0x44,0xb4,0x05,0x54,0x85,
           0x52,0x0d,0x92,0x0a,0x56,0x6a,0x56,0x02,0x6d,0x02,0x6a,0x41,0xda,0x02,
           0xb2,0xa1,0xa9,0x05,0x49,0x0d,0x0a,0x6d,0x2a,0x09,0x56,0x01,0xad,0x50,
           0x6d,0x01,0xd9,0x02,0xd1,0x3a,0xa8,0x05,0x29,0x85,0xa5,0x0c,0x2a,0x09,
           0x96,0x54,0xb6,0x08,0x6c,0x09,0x64,0x45,0xd4,0x0a,0xa4,0x05,0x51,0x25,
           0x95,0x0a,0x2a,0x72,0x5b,0x04,0xb6,0x04,0xac,0x52,0x6a,0x05,0xd2,0x0a,
           0xa2,0x4a,0x4a,0x05,0x55,0x94,0x2d,0x0a,0x5a,0x02,0x75,0x61,0xb5,0x02,
           0x6a,0x03,0x61,0x45,0xa9,0x0a,0x4a,0x05,0x25,0x25,0x2d,0x09,0x9a,0x68,
           0xda,0x08,0xb4,0x09,0xa8,0x59,0x54,0x03,0xa5,0x0a,0x91,0x3a,0x96,0x04,
           0xad,0xb0,0xad,0x04,0xda,0x04,0xf4,0x62,0xb4,0x05,0x54,0x0b,0x44,0x5d,
           0x52,0x0a,0x95,0x04,0x55,0x22,0x6d,0x02,0x5a,0x71,0xda,0x02,0xaa,0x05,
           0xb2,0x55,0x49,0x0b,0x4a,0x0a,0x2d,0x39,0x36,0x01,0x6d,0x80,0x6d,0x01,
           0xd9,0x02,0xe9,0x6a,0xa8,0x05,0x29,0x0b,0x9a,0x4c,0xaa,0x08,0xb6,0x08,
           0xb4,0x38,0x6c,0x09,0x54,0x75,0xd4,0x0a,0xa4,0x05,0x45,0x55,0x95,0x0a,
           0x9a,0x04,0x55,0x44,0xb5,0x04,0x6a,0x82,0x6a,0x05,0xd2,0x0a,0x92,0x6a,
           0x4a,0x05,0x55,0x0a,0x2a,0x4a,0x5a,0x02,0xb5,0x02,0xb2,0x31,0x69,0x03,
           0x31,0x73,0xa9,0x0a,0x4a,0x05,0x2d,0x55,0x2d,0x09,0x5a,0x01,0xd5,0x48,
           0xb4,0x09,0x68,0x89,0x54,0x0b,0xa4,0x0a,0xa5,0x6a,0x95,0x04,0xad,0x08,
           0x6a,0x44,0xda,0x04,0x74,0x05,0xb0,0x25,0x54,0x03
        };

        // 大闰月的闰年年份
        private static int[] bigLeapMonthYears = { 6, 14, 19, 25, 33, 36, 38, 41, 44, 52, 55, 79, 117, 136, 147, 150, 155, 158, 185, 193 };

工具函数

1 计算某年某月的天数

通过这个函数 我们可以进一步求得某一年的农历天数

        public static int DaysInChineseMonth(int y, int m)
        {
            // 注意：闰月m < 0
            int index = y - baseChineseYear;
            int v = 0;
            int l = 0;
            int d = 30;
            if (1 <= m && m <= 8)
            {
                v = chineseMonths[2 * index];
                l = m - 1;
                if (((v >> l) & 0x01) == 1) d = 29;
            }
            else if (9 <= m && m <= 12)
            {
                v = chineseMonths[2 * index + 1];
                l = m - 9;
                if (((v >> l) & 0x01) == 1) d = 29;
            }
            else
            {
                v = chineseMonths[2 * index + 1];
                v = (v >> 4) & 0x0F;
                if (v != Math.Abs(m))
                {
                    d = 0;
                }
                else
                {
                    d = 29;
                    for (int i = 0; i < bigLeapMonthYears.Length; i++)
                    {
                        if (bigLeapMonthYears[i] == index)
                        {
                            d = 30;
                            break;
                        }
                    }
                }
            }
            return d;
        }

2 某年某月的下一个月 农历不是每年都12个月，所以不能简单的累加，我们需要知道每年的闰月

        public static int NextChineseMonth(int y, int m)
        {
            int n = Math.Abs(m) + 1;
            if (m > 0)
            {
                int index = y - baseChineseYear + baseIndex;
                int v = chineseMonths[2 * index + 1];
                v = (v >> 4) & 0x0F;
                if (v == m) n = -m;
            }
            if (n == 13) n = 1;
            return n;
        }

通过以上两个函数 我们就可以知道每个农历年的天数
从公历计算到农历的伪代码如下：

    1> 获得了公历日期到1901年春节（公历为1901 2 19）的日期差 days
    2> 从1901年春节起 开始计算每个月的天数，从days中减去，月份和年份合理增加
    3> 直到days为0 

从农历到公历的伪代码如下
    1> 从目标日期计算到1901年春节的日期差 days （主要方法参照2>）
    2> 知道了days 然后TimeSpan 加下就得到了目标的DateTime