core/clock/moon.c
| Line | Branch | Exec | Source |
|---|---|---|---|
| 1 | /** | ||
| 2 | * @file moon.c | ||
| 3 | * @brief Pure moon-phase math, host-testable off-device. | ||
| 4 | * | ||
| 5 | * @ingroup lib_core | ||
| 6 | */ | ||
| 7 | #include "clock/moon.h" | ||
| 8 | |||
| 9 | 18 | int32_t moon_age_sec(time_t utc) | |
| 10 | { | ||
| 11 | // the offset from the epoch fits 32 bits until 2068 which outlives the watch. | ||
| 12 | // staying in 32 bits keeps the 64 bit division helpers out of the binary | ||
| 13 | 18 | int32_t age = (int32_t)(utc - MOON_EPOCH_UTC) % MOON_SYNODIC_SEC; | |
| 14 |
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18 | if (age < 0) |
| 15 | { | ||
| 16 | 1 | age += MOON_SYNODIC_SEC; | |
| 17 | } | ||
| 18 | |||
| 19 | 18 | return age; | |
| 20 | } | ||
| 21 | |||
| 22 | 6 | int moon_glyph_index(time_t utc, int count) | |
| 23 | { | ||
| 24 |
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6 | if (count <= 0) |
| 25 | { | ||
| 26 | 2 | return 0; | |
| 27 | } | ||
| 28 | |||
| 29 | // round the age to the nearest of count evenly spaced glyphs around the ring. | ||
| 30 | // age times count tops out around 71 million for the 28 glyph ring so int32 holds it | ||
| 31 | 4 | int32_t age = moon_age_sec(utc); | |
| 32 | 4 | int idx = (int)(((age * count) + MOON_SYNODIC_SEC / 2) / MOON_SYNODIC_SEC); | |
| 33 | 4 | return idx % count; | |
| 34 | } | ||
| 35 | |||
| 36 | 3 | int moon_illumination_pct(time_t utc) | |
| 37 | { | ||
| 38 | 3 | int32_t age = moon_age_sec(utc); | |
| 39 | 3 | int32_t half = MOON_SYNODIC_SEC / 2; | |
| 40 | |||
| 41 | // a triangle from new to full and back. not the true cosine curve, but close enough | ||
| 42 | // for a percent readout and it stays pure integer math | ||
| 43 | 5 | int32_t lit = age <= half ? (age * 100) / half | |
| 44 |
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3 | : ((MOON_SYNODIC_SEC - age) * 100) / half; |
| 45 | 3 | return (int)lit; | |
| 46 | } | ||
| 47 | |||
| 48 | 8 | int moon_days_to_phase(time_t utc, bool to_full) | |
| 49 | { | ||
| 50 |
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8 | int32_t target = to_full ? MOON_SYNODIC_SEC / 2 : MOON_SYNODIC_SEC; |
| 51 | 8 | int32_t until = target - moon_age_sec(utc); | |
| 52 |
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8 | if (until < 0) |
| 53 | { | ||
| 54 | // just past the target so the next one is almost a whole cycle away | ||
| 55 | 3 | until += MOON_SYNODIC_SEC; | |
| 56 | } | ||
| 57 |
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8 | if (until >= MOON_SYNODIC_SEC) |
| 58 | { | ||
| 59 | // right on the new moon the age is 0, which puts the target a whole cycle out | ||
| 60 | 1 | until -= MOON_SYNODIC_SEC; | |
| 61 | } | ||
| 62 | |||
| 63 | // half a day either side of the moon counts as now. a moon that was full six hours ago is | ||
| 64 | // still tonight's, and rounding a nearly whole cycle would read 30 | ||
| 65 |
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8 | if (until > MOON_SYNODIC_SEC - 43200) |
| 66 | { | ||
| 67 | 1 | return 0; | |
| 68 | } | ||
| 69 | |||
| 70 | // whole days rounded to the nearest so half a day out still reads right | ||
| 71 | 7 | return (int)((until + 43200) / 86400); | |
| 72 | } | ||
| 73 | |||
| 74 | 2 | const char *moon_phase_name(time_t utc) | |
| 75 | { | ||
| 76 | static const char *names[8] = { | ||
| 77 | "NEW", "WAX CRES", "1ST QTR", "WAX GIB", | ||
| 78 | "FULL", "WAN GIB", "3RD QTR", "WAN CRES", | ||
| 79 | }; | ||
| 80 | |||
| 81 | 2 | return names[moon_glyph_index(utc, 8)]; | |
| 82 | } | ||
| 83 |