Saturday Is Coming Faster - Convert year_month_day to Weekday Faster - Part 2
summary
Claims a new calendar routine that converts year_month_day to weekday up to 3x faster than the usual chrono path and shows the actual arithmetic behind it: using octal representation to exploit modulus 7, constructing a fractional multiplier M with 32 important bits after the point, replacing division by a multiply plus a right shift by 29 bits, and deriving the exact constant so the trick reproduces correct weekdays across the tested range.
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