a3381faf81
The divLarge code contained "todo"s about avoiding alias and clear calls in the initialization of variables. By rearranging the order of initialization and always using an auxiliary variable for the shifted divisor, all of these calls can be safely avoided. On average, normalizing the divisor (shift>0) is required 31/32 or 63/64 of the time. If one always performs the shift into an auxiliary variable first, this avoids the need to check for aliasing of vIn in the output variables u and z. The remainder u is initialized via a left shift of uIn and thus needs no alias check against uIn. Since uIn and vIn were both used, z needs no alias checks except against u which is used for storage of the remainder. This change has a minimal impact on performance (see below), but cleans up the initialization code and eliminates the "todo"s. name old time/op new time/op delta Div/20/10-4 86.7ns ± 6% 85.7ns ± 5% ~ (p=0.841 n=5+5) Div/200/100-4 523ns ± 5% 502ns ± 3% -4.13% (p=0.024 n=5+5) Div/2000/1000-4 2.55µs ± 3% 2.59µs ± 5% ~ (p=0.548 n=5+5) Div/20000/10000-4 80.4µs ± 4% 80.0µs ± 2% ~ (p=1.000 n=5+5) Div/200000/100000-4 6.43ms ± 6% 6.35ms ± 4% ~ (p=0.548 n=5+5) Fixes #22928 Change-Id: I30d8498ef1cf8b69b0f827165c517bc25a5c32d7 Reviewed-on: https://go-review.googlesource.com/130775 Reviewed-by: Robert Griesemer <gri@golang.org> |
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