From 3acb265c9ee8ac26ab43361997a5db0e4b9fa47c Mon Sep 17 00:00:00 2001 From: bunnei Date: Fri, 19 Feb 2021 18:04:23 -0800 Subject: common: wall_clock: Fix integer overflow with StandardWallClock. - Previous optimized impl. resulted in an integer overflow, so revert. - This is our slow/fallback path that should never be really be used, so the optimization in unimportant. --- src/common/uint128.h | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) (limited to 'src/common/uint128.h') diff --git a/src/common/uint128.h b/src/common/uint128.h index 83560a9ce..4780b2f9d 100644 --- a/src/common/uint128.h +++ b/src/common/uint128.h @@ -98,4 +98,24 @@ namespace Common { #endif } +// This function divides a u128 by a u32 value and produces two u64 values: +// the result of division and the remainder +[[nodiscard]] static inline std::pair Divide128On32(u128 dividend, u32 divisor) { + u64 remainder = dividend[0] % divisor; + u64 accum = dividend[0] / divisor; + if (dividend[1] == 0) + return {accum, remainder}; + // We ignore dividend[1] / divisor as that overflows + const u64 first_segment = (dividend[1] % divisor) << 32; + accum += (first_segment / divisor) << 32; + const u64 second_segment = (first_segment % divisor) << 32; + accum += (second_segment / divisor); + remainder += second_segment % divisor; + if (remainder >= divisor) { + accum++; + remainder -= divisor; + } + return {accum, remainder}; +} + } // namespace Common -- cgit v1.2.3