core/clock/solar.c
| Line | Branch | Exec | Source |
|---|---|---|---|
| 1 | /** | ||
| 2 | * @file solar.c | ||
| 3 | * @brief How the day's light is going, worked out from three plain clock readings. | ||
| 4 | * | ||
| 5 | * @ingroup lib_core | ||
| 6 | */ | ||
| 7 | #include "clock/solar.h" | ||
| 8 | |||
| 9 | /// A day's worth of minutes, for wrapping the night span across midnight | ||
| 10 | #define MINUTES_PER_DAY 1440 | ||
| 11 | |||
| 12 | /** | ||
| 13 | * @brief Whether all three readings are real minutes of the day, so the maths below is not run on a | ||
| 14 | * missing time. Sunrise and sunset landing on the same minute also count as missing, since that | ||
| 15 | * could be a sun that never sets or one that never rises and there is no telling which. | ||
| 16 | * | ||
| 17 | * @param rise Sunrise, minutes past midnight, or -1 for no data. | ||
| 18 | * @param set Sunset, minutes past midnight, or -1 for no data. | ||
| 19 | * @param now The clock, minutes past midnight, or -1 for no data. | ||
| 20 | * @return True when all three are real readings and the sun both rises and sets. | ||
| 21 | */ | ||
| 22 | 23 | static bool have_all(int rise, int set, int now) | |
| 23 | { | ||
| 24 | // a reading below zero turns into a huge unsigned one, so each check covers both ends | ||
| 25 | 45 | return (unsigned)rise < MINUTES_PER_DAY && | |
| 26 |
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22 | (unsigned)set < MINUTES_PER_DAY && |
| 27 |
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45 | (unsigned)now < MINUTES_PER_DAY && |
| 28 | rise != set; | ||
| 29 | } | ||
| 30 | |||
| 31 | /** | ||
| 32 | * @brief Minutes going forward round the clock from one reading to another. | ||
| 33 | * | ||
| 34 | * Sunset falls after midnight in a high latitude summer, so the daylight can run from 03:00 round | ||
| 35 | * to 00:30. Measuring everything forward from sunrise this way covers that and an ordinary day | ||
| 36 | * with the same maths. | ||
| 37 | * | ||
| 38 | * @param from The earlier reading, minutes past midnight. | ||
| 39 | * @param to The later reading, minutes past midnight. | ||
| 40 | * @return 0 to 1439. | ||
| 41 | */ | ||
| 42 | 46 | static int forward(int from, int to) | |
| 43 | { | ||
| 44 | 46 | int minutes = to - from; | |
| 45 |
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46 | if (minutes < 0) |
| 46 | { | ||
| 47 | 20 | minutes += MINUTES_PER_DAY; | |
| 48 | } | ||
| 49 | 46 | return minutes; | |
| 50 | } | ||
| 51 | |||
| 52 | 9 | int solar_day_progress(int rise, int set, int now) | |
| 53 | { | ||
| 54 |
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9 | if (!have_all(rise, set, now)) |
| 55 | { | ||
| 56 | 3 | return -1; | |
| 57 | } | ||
| 58 | |||
| 59 | 6 | int span = forward(rise, set); | |
| 60 | 6 | int elapsed = forward(rise, now); | |
| 61 |
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6 | if (elapsed > span) |
| 62 | { | ||
| 63 | 3 | return -1; // past sunset and not yet round to sunrise, so it is night | |
| 64 | } | ||
| 65 | 3 | return (elapsed * 100) / span; | |
| 66 | } | ||
| 67 | |||
| 68 | 6 | int solar_night_progress(int rise, int set, int now) | |
| 69 | { | ||
| 70 |
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6 | if (!have_all(rise, set, now) || forward(rise, now) <= forward(rise, set)) |
| 71 | { | ||
| 72 | 3 | return -1; | |
| 73 | } | ||
| 74 | |||
| 75 | // sunset to the next sunrise, which is whatever the daylight leaves of the day | ||
| 76 | 3 | int span = MINUTES_PER_DAY - forward(rise, set); | |
| 77 | 3 | return (forward(set, now) * 100) / span; | |
| 78 | } | ||
| 79 | |||
| 80 | 8 | int solar_next_event(int rise, int set, int now, bool *is_sunrise) | |
| 81 | { | ||
| 82 |
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8 | if (!have_all(rise, set, now)) |
| 83 | { | ||
| 84 | 2 | return -1; | |
| 85 | } | ||
| 86 | |||
| 87 |
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6 | if (forward(rise, now) < forward(rise, set)) |
| 88 | { | ||
| 89 | 3 | *is_sunrise = false; | |
| 90 | 3 | return forward(now, set); | |
| 91 | } | ||
| 92 | 3 | *is_sunrise = true; | |
| 93 | 3 | return forward(now, rise); | |
| 94 | } | ||
| 95 |