IliaDenisov
75 lines
1.3 KiB
Go
75 lines
1.3 KiB
Go
package world
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import "math/bits"
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// u128 is an unsigned 128-bit integer for safe squared comparisons.
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type u128 struct{ hi, lo uint64 }
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func u128FromMul64(a, b uint64) u128 {
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hi, lo := bits.Mul64(a, b)
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return u128{hi: hi, lo: lo}
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}
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func u128Add(a, b u128) u128 {
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lo := a.lo + b.lo
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hi := a.hi + b.hi
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if lo < a.lo {
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hi++
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}
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return u128{hi: hi, lo: lo}
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}
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func u128Cmp(a, b u128) int {
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if a.hi < b.hi {
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return -1
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}
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if a.hi > b.hi {
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return 1
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}
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if a.lo < b.lo {
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return -1
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}
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if a.lo > b.lo {
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return 1
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}
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return 0
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}
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func abs64(x int64) int64 {
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if x < 0 {
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return -x
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}
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return x
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}
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func sqU128Int64(x int64) u128 {
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u := uint64(abs64(x))
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return u128FromMul64(u, u)
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}
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func distSqU128(dx, dy int64) u128 {
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return u128Add(sqU128Int64(dx), sqU128Int64(dy))
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}
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// shortestTorusDelta returns the shortest signed delta from a->b on a torus axis of size.
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// It is deterministic in tie cases (size even, exactly half): chooses negative direction.
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func shortestTorusDelta(a, b, size int) int64 {
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d := int64(b - a)
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s := int64(size)
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half := s / 2
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// Normalize d into (-s, s).
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d = d % s
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if d <= -half {
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d += s
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} else if d > half {
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d -= s
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}
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// Tie case when size even and d == +half: choose -half.
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if s%2 == 0 && d == half {
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d = -half
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}
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return d
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}
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