76 lines
2.4 KiB
Go
76 lines
2.4 KiB
Go
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package basic
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import (
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"math"
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"sync"
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"sync/atomic"
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)
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// Nutation2000B 是 jd 的纯函数，但升落、星历与掩星路径会对同一批瞬时反复求值：一条计算链里
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// 地球自转、状态上下文与几何装配各自求一次同一个瞬时。这里用有界直接映射表记住结果：
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// 槽位固定、无分配、RWMutex 保证 c-shared 宿主多线程安全。章动只依赖传入的 jd，与 ΔT 世代无关。
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// Nutation2000B is a pure function of jd, yet the rise/set, ephemeris and occultation chains evaluate
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// it repeatedly for the same instants from independent code paths. This bounded direct-mapped memo
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// removes that redundancy with fixed slots, no allocation and an RWMutex for the c-shared host.
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// Nutation depends only on its argument, so no ΔT generation stamp is needed.
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const nutationMemoBits = 13
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const nutationMemoSize = 1 << nutationMemoBits
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type nutationMemoEntry struct {
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// key 是 math.Float64bits(jd)+1，0 表示空槽（避免 jd=0 与空槽同码）。
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key uint64
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dpsi, deps float64
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}
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var (
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nutationMemoMu sync.RWMutex
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nutationMemoTable [nutationMemoSize]nutationMemoEntry
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nutationMemoHits uint64
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nutationMemoMiss uint64
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)
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func nutationMemoIndex(jd float64) uint64 {
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bits := math.Float64bits(jd)
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return (bits ^ (bits >> 31)) & (nutationMemoSize - 1)
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}
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func nutationMemoLoad(jd float64) (float64, float64, bool) {
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key := math.Float64bits(jd) + 1
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entry := &nutationMemoTable[nutationMemoIndex(jd)]
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nutationMemoMu.RLock()
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entryKey, dpsi, deps := entry.key, entry.dpsi, entry.deps
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nutationMemoMu.RUnlock()
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if key != 0 && entryKey == key {
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atomic.AddUint64(&nutationMemoHits, 1)
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return dpsi, deps, true
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}
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atomic.AddUint64(&nutationMemoMiss, 1)
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return 0, 0, false
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}
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func nutationMemoStore(jd, dpsi, deps float64) {
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key := math.Float64bits(jd) + 1
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if key == 0 {
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return
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}
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nutationMemoMu.Lock()
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nutationMemoTable[nutationMemoIndex(jd)] = nutationMemoEntry{key: key, dpsi: dpsi, deps: deps}
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nutationMemoMu.Unlock()
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}
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// nutationMemoStats 返回命中/未命中计数，供测试守护命中率。
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func nutationMemoStats() (uint64, uint64) {
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return atomic.LoadUint64(&nutationMemoHits), atomic.LoadUint64(&nutationMemoMiss)
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}
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func resetNutationMemo() {
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nutationMemoMu.Lock()
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for i := range nutationMemoTable {
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nutationMemoTable[i] = nutationMemoEntry{}
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}
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nutationMemoMu.Unlock()
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atomic.StoreUint64(&nutationMemoHits, 0)
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atomic.StoreUint64(&nutationMemoMiss, 0)
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}
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