From bf8990dcb02749d5d9e5915f5449ad91ad49ae2d Mon Sep 17 00:00:00 2001 From: "J. Nick Koston" Date: Sun, 1 Mar 2026 23:27:38 -1000 Subject: [PATCH] [core] Document exact safe input range for fast_div1000_32 --- esphome/core/helpers.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/esphome/core/helpers.h b/esphome/core/helpers.h index fc0b9cd99f..4f3930465d 100644 --- a/esphome/core/helpers.h +++ b/esphome/core/helpers.h @@ -552,7 +552,7 @@ inline ESPHOME_ALWAYS_INLINE uint32_t fast_div1000_32(uint64_t us) { uint32_t lo = static_cast(us); uint32_t hi = static_cast(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);