Atlas - SDL_time.c
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1/*
2  Simple DirectMedia Layer
3  Copyright (C) 1997-2026 Sam Lantinga <[email protected]>
4
5  This software is provided 'as-is', without any express or implied
6  warranty.  In no event will the authors be held liable for any damages
7  arising from the use of this software.
8
9  Permission is granted to anyone to use this software for any purpose,
10  including commercial applications, and to alter it and redistribute it
11  freely, subject to the following restrictions:
12
13  1. The origin of this software must not be misrepresented; you must not
14     claim that you wrote the original software. If you use this software
15     in a product, an acknowledgment in the product documentation would be
16     appreciated but is not required.
17  2. Altered source versions must be plainly marked as such, and must not be
18     misrepresented as being the original software.
19  3. This notice may not be removed or altered from any source distribution.
20*/
21#include "SDL_internal.h"
22
23#include "SDL_time_c.h"
24
25/* The following algorithms are based on those of Howard Hinnant and are in the public domain.
26 *
27 * http://howardhinnant.github.io/date_algorithms.html
28 */
29
30/* Given a calendar date, returns days since Jan 1 1970, and optionally
31 * the day of the week [0-6, 0 is Sunday] and day of the year [0-365].
32 */
33Sint64 SDL_CivilToDays(int year, int month, int day, int *day_of_week, int *day_of_year)
34{
35    year -= month <= 2;
36    const int era = (year >= 0 ? year : year - 399) / 400;
37    const unsigned yoe = (unsigned)(year - era * 400);                                  // [0, 399]
38    const unsigned doy = (153 * (month > 2 ? month - 3 : month + 9) + 2) / 5 + day - 1; // [0, 365]
39    const unsigned doe = yoe * 365 + yoe / 4 - yoe / 100 + doy;                         // [0, 146096]
40    const Sint64 z = (Sint64)(era) * 146097 + (Sint64)(doe)-719468;
41
42    if (day_of_week) {
43        *day_of_week = (int)(z >= -4 ? (z + 4) % 7 : (z + 5) % 7 + 6);
44    }
45    if (day_of_year) {
46        // This algorithm considers March 1 to be the first day of the year, so offset by Jan + Feb.
47        if (doy > 305) {
48            // Day 0 is the first day of the year.
49            *day_of_year = doy - 306;
50        } else {
51            const int doy_offset = 59 + (!(year % 4) && ((year % 100) || !(year % 400)));
52            *day_of_year = doy + doy_offset;
53        }
54    }
55
56    return z;
57}
58
59bool SDL_GetDateTimeLocalePreferences(SDL_DateFormat *dateFormat, SDL_TimeFormat *timeFormat)
60{
61    // Default to ISO 8061 date format, as it is unambiguous, and 24 hour time.
62    if (dateFormat) {
63        *dateFormat = SDL_DATE_FORMAT_YYYYMMDD;
64    }
65    if (timeFormat) {
66        *timeFormat = SDL_TIME_FORMAT_24HR;
67    }
68
69    SDL_GetSystemTimeLocalePreferences(dateFormat, timeFormat);
70
71    return true;
72}
73
74int SDL_GetDaysInMonth(int year, int month)
75{
76    static const int DAYS_IN_MONTH[] = {
77        31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
78    };
79
80    if (month < 1 || month > 12) {
81        SDL_SetError("Month out of range [1-12], requested: %i", month);
82        return -1;
83    }
84
85    int days = DAYS_IN_MONTH[month - 1];
86
87    /* A leap year occurs every 4 years...
88     * but not every 100 years...
89     * except for every 400 years.
90     */
91    if (month == 2 && (!(year % 4) && ((year % 100) || !(year % 400)))) {
92        ++days;
93    }
94
95    return days;
96}
97
98int SDL_GetDayOfYear(int year, int month, int day)
99{
100    int dayOfYear;
101
102    if (month < 1 || month > 12) {
103        SDL_SetError("Month out of range [1-12], requested: %i", month);
104        return -1;
105    }
106    if (day < 1 || day > SDL_GetDaysInMonth(year, month)) {
107        SDL_SetError("Day out of range [1-%i], requested: %i", SDL_GetDaysInMonth(year, month), month);
108        return -1;
109    }
110
111    SDL_CivilToDays(year, month, day, NULL, &dayOfYear);
112    return dayOfYear;
113}
114
115int SDL_GetDayOfWeek(int year, int month, int day)
116{
117    int dayOfWeek;
118
119    if (month < 1 || month > 12) {
120        SDL_SetError("Month out of range [1-12], requested: %i", month);
121        return -1;
122    }
123    if (day < 1 || day > SDL_GetDaysInMonth(year, month)) {
124        SDL_SetError("Day out of range [1-%i], requested: %i", SDL_GetDaysInMonth(year, month), month);
125        return -1;
126    }
127
128    SDL_CivilToDays(year, month, day, &dayOfWeek, NULL);
129    return dayOfWeek;
130}
131
132static bool SDL_DateTimeIsValid(const SDL_DateTime *dt)
133{
134    if (dt->month < 1 || dt->month > 12) {
135        SDL_SetError("Malformed SDL_DateTime: month out of range [1-12], current: %i", dt->month);
136        return false;
137    }
138
139    const int daysInMonth = SDL_GetDaysInMonth(dt->year, dt->month);
140    if (dt->day < 1 || dt->day > daysInMonth) {
141        SDL_SetError("Malformed SDL_DateTime: day of month out of range [1-%i], current: %i", daysInMonth, dt->month);
142        return false;
143    }
144    if (dt->hour < 0 || dt->hour > 23) {
145        SDL_SetError("Malformed SDL_DateTime: hour out of range [0-23], current: %i", dt->hour);
146        return false;
147    }
148    if (dt->minute < 0 || dt->minute > 59) {
149        SDL_SetError("Malformed SDL_DateTime: minute out of range [0-59], current: %i", dt->minute);
150        return false;
151    }
152    if (dt->second < 0 || dt->second > 60) {
153        SDL_SetError("Malformed SDL_DateTime: second out of range [0-60], current: %i", dt->second);
154        return false; // 60 accounts for a possible leap second.
155    }
156    if (dt->nanosecond < 0 || dt->nanosecond >= SDL_NS_PER_SECOND) {
157        SDL_SetError("Malformed SDL_DateTime: nanosecond out of range [0-999999999], current: %i", dt->nanosecond);
158        return false;
159    }
160
161    return true;
162}
163
164bool SDL_DateTimeToTime(const SDL_DateTime *dt, SDL_Time *ticks)
165{
166    static const Sint64 max_seconds = SDL_NS_TO_SECONDS(SDL_MAX_TIME) - 1;
167    static const Sint64 min_seconds = SDL_NS_TO_SECONDS(SDL_MIN_TIME) + 1;
168    bool result = true;
169
170    CHECK_PARAM(!dt) {
171        return SDL_InvalidParamError("dt");
172    }
173    CHECK_PARAM(!ticks) {
174        return SDL_InvalidParamError("ticks");
175    }
176    CHECK_PARAM(!SDL_DateTimeIsValid(dt)) {
177        // The validation function sets the error string.
178        return false;
179    }
180
181    *ticks = SDL_CivilToDays(dt->year, dt->month, dt->day, NULL, NULL) * SDL_SECONDS_PER_DAY;
182    *ticks += (((dt->hour * 60) + dt->minute) * 60) + dt->second - dt->utc_offset;
183    if (*ticks > max_seconds || *ticks < min_seconds) {
184        *ticks = SDL_clamp(*ticks, min_seconds, max_seconds);
185        result = SDL_SetError("Date out of range for SDL_Time representation; SDL_Time value clamped");
186    }
187    *ticks = SDL_SECONDS_TO_NS(*ticks) + dt->nanosecond;
188
189    return result;
190}
191
192#define DELTA_EPOCH_1601_100NS (11644473600ll * 10000000ll) // [100 ns] (100 ns units between 1601-01-01 and 1970-01-01, 11644473600 seconds)
193
194void SDL_TimeToWindows(SDL_Time ticks, Uint32 *dwLowDateTime, Uint32 *dwHighDateTime)
195{
196    /* Convert nanoseconds to Win32 ticks.
197     * SDL_Time has a range of roughly 292 years, so even SDL_MIN_TIME can't underflow the Win32 epoch.
198     */
199    const Uint64 wtime = (Uint64)((ticks / 100) + DELTA_EPOCH_1601_100NS);
200
201    if (dwLowDateTime) {
202        *dwLowDateTime = (Uint32)wtime;
203    }
204
205    if (dwHighDateTime) {
206        *dwHighDateTime = (Uint32)(wtime >> 32);
207    }
208}
209
210SDL_Time SDL_TimeFromWindows(Uint32 dwLowDateTime, Uint32 dwHighDateTime)
211{
212    static const Uint64 wintime_min = (Uint64)((SDL_MIN_TIME / 100) + DELTA_EPOCH_1601_100NS);
213    static const Uint64 wintime_max = (Uint64)((SDL_MAX_TIME / 100) + DELTA_EPOCH_1601_100NS);
214
215    Uint64 wtime = (((Uint64)dwHighDateTime << 32) | dwLowDateTime);
216
217    // Clamp the windows time range to the SDL_Time min/max
218    wtime = SDL_clamp(wtime, wintime_min, wintime_max);
219
220    return (SDL_Time)(wtime - DELTA_EPOCH_1601_100NS) * 100;
221}
222
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