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Diffstat (limited to 'lib/date.h')
| -rw-r--r-- | lib/date.h | 139 |
1 files changed, 139 insertions, 0 deletions
diff --git a/lib/date.h b/lib/date.h new file mode 100644 index 0000000..6d8b060 --- /dev/null +++ b/lib/date.h @@ -0,0 +1,139 @@ +/* + * Copyright (c) 2026 Dylan Araps + * + * Permission is hereby granted, free of charge, to any person obtaining a copy + * of this software and associated documentation files (the "Software"), to deal + * in the Software without restriction, including without limitation the rights + * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell + * copies of the Software, and to permit persons to whom the Software is + * furnished to do so, subject to the following conditions: + * + * The above copyright notice and this permission notice shall be included in all + * copies or substantial portions of the Software. + * + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE + * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, + * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE + * SOFTWARE. + */ +#ifndef DYLAN_DATE_H +#define DYLAN_DATE_H + +// +// Fast date algorithm, C implementation. +// Source: https://www.benjoffe.com/fast-date-64 +// +#include <stddef.h> +#include <stdint.h> + +#include "util.h" + +#define C1 505054698555331ull // floor(2^64 * 4 / 146097) +#define C2 50504432782230121ull // ceil(2^64 * 4 / 1461) +#define C3 8619973866219416ull // floor(2^64 / 2140) + +#define SCALE 32u +#define SHIFT0 (30556u * SCALE) +#define SHIFT1 (5980u * SCALE) + +#if defined(__SIZEOF_INT128__) +#define ERAS 4726498270ull +#define D_SHIFT ((u64)(146097ull * ERAS - 719469ull)) +#define Y_SHIFT ((u64)(400ull * ERAS - 1ull)) + +static inline u64 +mulhi(u64 a, u64 b) +{ + __uint128_t p = (__uint128_t)a * (__uint128_t)b; + return (u64)(p >> 64); +} + +static inline void +mul128(u64 a, u64 b, u64 *hi, u64 *lo) +{ + __uint128_t p = (__uint128_t)a * (__uint128_t)b; + *hi = (u64)(p >> 64); + *lo = (u64)p; +} + +#else + +#define ERAS 14704u +#define D_SHIFT ((u64)(146097ull * (u64)ERAS - 719469ull)) +#define Y_SHIFT ((u64)(400ull * (u64)ERAS - 1ull)) + +static inline u64 +mulhi(u64 a, u64 b) +{ + u64 a0 = (u32)a; + u64 a1 = a >> 32; + u64 b0 = (u32)b; + u64 b1 = b >> 32; + u64 p00 = a0 * b0; + u64 p01 = a0 * b1; + u64 p10 = a1 * b0; + u64 p11 = a1 * b1; + u64 mid = (p00 >> 32) + (u32)p01 + (u32)p10; + return p11 + (p01 >> 32) + (p10 >> 32) + (mid >> 32); +} + +static inline void +mul128(u64 a, u64 b, u64 *hi, u64 *lo) +{ + u64 a0 = (u32)a; + u64 a1 = a >> 32; + u64 b0 = (u32)b; + u64 b1 = b >> 32; + u64 p00 = a0 * b0; + u64 p01 = a0 * b1; + u64 p10 = a1 * b0; + u64 p11 = a1 * b1; + u64 mid = (p00 >> 32) + (u32)p01 + (u32)p10; + *hi = p11 + (p01 >> 32) + (p10 >> 32) + (mid >> 32); + *lo = (mid << 32) | (u32)p00; +} + +#endif // defined(__SIZEOF_INT128__) + +static inline void +ut_to_date(s32 day, s32 *Y, u32 *M, u32 *D) +{ + u64 rev = (u64)D_SHIFT - (u64)(s64)day; // Reverse day count. + u64 cen = mulhi(C1, rev); // Divide 36524.25 + u64 jul = rev - cen / 4u + cen; // Julian map. + u64 num_hi, num_lo; + mul128(C2, jul, &num_hi, &num_lo); // Divide 365.25 + u64 yrs64 = (u64)Y_SHIFT - (u64)num_hi; // Forward year. + u64 yrs = (u32)yrs64; + u32 ypt = (u32)mulhi((u64)(24451u * SCALE), num_lo); // Year (backwards). + u32 bump = (ypt < (3952u * SCALE)); // Jan or Feb. + u32 shift = bump ? SHIFT1 : SHIFT0; // Month offset. + u32 N = (u32)((yrs % 4u) * (16u * SCALE) + shift - ypt); // Leap years. + u32 m = N / (2048u * SCALE); + u32 d = (u32)mulhi(C3, (u64)(N % (2048u * SCALE))); // Divide 2140 + *Y = (s32)yrs + (s32)bump; + *M = m; + *D = d + 1u; +} + +static inline void +ut_to_date_time(s64 tz, s32 day, s32 *Y, u32 *M, u32 *D, u32 *h, u32 *m, u32 *s) +{ + s64 us = tz + day; + s32 days = (s32)(us / 86400); + s32 r = (s32)(us % 86400); + if (r < 0) { r += 86400; days -= 1; } + ut_to_date(days, Y, M, D); + u32 hr = r / 3600; + r -= hr * 3600; + *h = hr; + u32 mn = r / 60; + *m = mn; + *s = r - mn * 60; +} + +#endif // DYLAN_DATE_H + |