Atlas - SDL_time.c
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1/*
2  Simple DirectMedia Layer
3  Copyright (C) 1997-2025 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
36    year -= month <= 2;
37    const int era = (year >= 0 ? year : year - 399) / 400;
38    const unsigned yoe = (unsigned)(year - era * 400);                                  // [0, 399]
39    const unsigned doy = (153 * (month > 2 ? month - 3 : month + 9) + 2) / 5 + day - 1; // [0, 365]
40    const unsigned doe = yoe * 365 + yoe / 4 - yoe / 100 + doy;                         // [0, 146096]
41    const Sint64 z = (Sint64)(era) * 146097 + (Sint64)(doe)-719468;
42
43    if (day_of_week) {
44        *day_of_week = (int)(z >= -4 ? (z + 4) % 7 : (z + 5) % 7 + 6);
45    }
46    if (day_of_year) {
47        // This algorithm considers March 1 to be the first day of the year, so offset by Jan + Feb.
48        if (doy > 305) {
49            // Day 0 is the first day of the year.
50            *day_of_year = doy - 306;
51        } else {
52            const int doy_offset = 59 + (!(year % 4) && ((year % 100) || !(year % 400)));
53            *day_of_year = doy + doy_offset;
54        }
55    }
56
57    return z;
58}
59
60bool SDL_GetDateTimeLocalePreferences(SDL_DateFormat *dateFormat, SDL_TimeFormat *timeFormat)
61{
62    // Default to ISO 8061 date format, as it is unambiguous, and 24 hour time.
63    if (dateFormat) {
64        *dateFormat = SDL_DATE_FORMAT_YYYYMMDD;
65    }
66    if (timeFormat) {
67        *timeFormat = SDL_TIME_FORMAT_24HR;
68    }
69
70    SDL_GetSystemTimeLocalePreferences(dateFormat, timeFormat);
71
72    return true;
73}
74
75int SDL_GetDaysInMonth(int year, int month)
76{
77    static const int DAYS_IN_MONTH[] = {
78        31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
79    };
80
81    if (month < 1 || month > 12) {
82        SDL_SetError("Month out of range [1-12], requested: %i", month);
83        return -1;
84    }
85
86    int days = DAYS_IN_MONTH[month - 1];
87
88    /* A leap year occurs every 4 years...
89     * but not every 100 years...
90     * except for every 400 years.
91     */
92    if (month == 2 && (!(year % 4) && ((year % 100) || !(year % 400)))) {
93        ++days;
94    }
95
96    return days;
97}
98
99int SDL_GetDayOfYear(int year, int month, int day)
100{
101    int dayOfYear;
102
103    if (month < 1 || month > 12) {
104        SDL_SetError("Month out of range [1-12], requested: %i", month);
105        return -1;
106    }
107    if (day < 1 || day > SDL_GetDaysInMonth(year, month)) {
108        SDL_SetError("Day out of range [1-%i], requested: %i", SDL_GetDaysInMonth(year, month), month);
109        return -1;
110    }
111
112    SDL_CivilToDays(year, month, day, NULL, &dayOfYear);
113    return dayOfYear;
114}
115
116int SDL_GetDayOfWeek(int year, int month, int day)
117{
118    int dayOfWeek;
119
120    if (month < 1 || month > 12) {
121        SDL_SetError("Month out of range [1-12], requested: %i", month);
122        return -1;
123    }
124    if (day < 1 || day > SDL_GetDaysInMonth(year, month)) {
125        SDL_SetError("Day out of range [1-%i], requested: %i", SDL_GetDaysInMonth(year, month), month);
126        return -1;
127    }
128
129    SDL_CivilToDays(year, month, day, &dayOfWeek, NULL);
130    return dayOfWeek;
131}
132
133static bool SDL_DateTimeIsValid(const SDL_DateTime *dt)
134{
135    if (dt->month < 1 || dt->month > 12) {
136        SDL_SetError("Malformed SDL_DateTime: month out of range [1-12], current: %i", dt->month);
137        return false;
138    }
139
140    const int daysInMonth = SDL_GetDaysInMonth(dt->year, dt->month);
141    if (dt->day < 1 || dt->day > daysInMonth) {
142        SDL_SetError("Malformed SDL_DateTime: day of month out of range [1-%i], current: %i", daysInMonth, dt->month);
143        return false;
144    }
145    if (dt->hour < 0 || dt->hour > 23) {
146        SDL_SetError("Malformed SDL_DateTime: hour out of range [0-23], current: %i", dt->hour);
147        return false;
148    }
149    if (dt->minute < 0 || dt->minute > 59) {
150        SDL_SetError("Malformed SDL_DateTime: minute out of range [0-59], current: %i", dt->minute);
151        return false;
152    }
153    if (dt->second < 0 || dt->second > 60) {
154        SDL_SetError("Malformed SDL_DateTime: second out of range [0-60], current: %i", dt->second);
155        return false; // 60 accounts for a possible leap second.
156    }
157    if (dt->nanosecond < 0 || dt->nanosecond >= SDL_NS_PER_SECOND) {
158        SDL_SetError("Malformed SDL_DateTime: nanosecond out of range [0-999999999], current: %i", dt->nanosecond);
159        return false;
160    }
161
162    return true;
163}
164
165bool SDL_DateTimeToTime(const SDL_DateTime *dt, SDL_Time *ticks)
166{
167    static const Sint64 max_seconds = SDL_NS_TO_SECONDS(SDL_MAX_TIME) - 1;
168    static const Sint64 min_seconds = SDL_NS_TO_SECONDS(SDL_MIN_TIME) + 1;
169    bool result = true;
170
171    CHECK_PARAM(!dt) {
172        return SDL_InvalidParamError("dt");
173    }
174    CHECK_PARAM(!ticks) {
175        return SDL_InvalidParamError("ticks");
176    }
177    CHECK_PARAM(!SDL_DateTimeIsValid(dt)) {
178        // The validation function sets the error string.
179        return false;
180    }
181
182    *ticks = SDL_CivilToDays(dt->year, dt->month, dt->day, NULL, NULL) * SDL_SECONDS_PER_DAY;
183    *ticks += (((dt->hour * 60) + dt->minute) * 60) + dt->second - dt->utc_offset;
184    if (*ticks > max_seconds || *ticks < min_seconds) {
185        *ticks = SDL_clamp(*ticks, min_seconds, max_seconds);
186        result = SDL_SetError("Date out of range for SDL_Time representation; SDL_Time value clamped");
187    }
188    *ticks = SDL_SECONDS_TO_NS(*ticks) + dt->nanosecond;
189
190    return result;
191}
192
193#define DELTA_EPOCH_1601_100NS (11644473600ll * 10000000ll) // [100 ns] (100 ns units between 1601-01-01 and 1970-01-01, 11644473600 seconds)
194
195void SDL_TimeToWindows(SDL_Time ticks, Uint32 *dwLowDateTime, Uint32 *dwHighDateTime)
196{
197    /* Convert nanoseconds to Win32 ticks.
198     * SDL_Time has a range of roughly 292 years, so even SDL_MIN_TIME can't underflow the Win32 epoch.
199     */
200    const Uint64 wtime = (Uint64)((ticks / 100) + DELTA_EPOCH_1601_100NS);
201
202    if (dwLowDateTime) {
203        *dwLowDateTime = (Uint32)wtime;
204    }
205
206    if (dwHighDateTime) {
207        *dwHighDateTime = (Uint32)(wtime >> 32);
208    }
209}
210
211SDL_Time SDL_TimeFromWindows(Uint32 dwLowDateTime, Uint32 dwHighDateTime)
212{
213    static const Uint64 wintime_min = (Uint64)((SDL_MIN_TIME / 100) + DELTA_EPOCH_1601_100NS);
214    static const Uint64 wintime_max = (Uint64)((SDL_MAX_TIME / 100) + DELTA_EPOCH_1601_100NS);
215
216    Uint64 wtime = (((Uint64)dwHighDateTime << 32) | dwLowDateTime);
217
218    // Clamp the windows time range to the SDL_Time min/max
219    wtime = SDL_clamp(wtime, wintime_min, wintime_max);
220
221    return (SDL_Time)(wtime - DELTA_EPOCH_1601_100NS) * 100;
222}
223
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