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[core] Document exact safe input range for fast_div1000_32

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J. Nick Koston
2026-03-01 23:27:38 -10:00
parent 263d6c1085
commit bf8990dcb0
1 changed files with 1 additions and 1 deletions
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esphome/core/helpers.h
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@@ -552,7 +552,7 @@ inline ESPHOME_ALWAYS_INLINE uint32_t fast_div1000_32(uint64_t us) {
uint32_t lo = static_cast<uint32_t>(us);
uint32_t hi = static_cast<uint32_t>(us >> 32);
// Combine remainder term: hi * (2^32 % 1000) + lo
// Note: hi * R fits in uint32_t when hi < UINT32_MAX / R (~14.5M), i.e. us < ~62 quadrillion
// Safe for us < (14510024 << 32), i.e. ~6.2e16 (~1,975 years of microseconds)
uint32_t adj = hi * R + lo;
// If adj overflowed, the true value is 2^32 + adj; apply the identity again
return hi * Q + (adj < lo ? (adj + R) / D + Q : adj / D);