The sha256 hash writer doesn't implement WriteString.
(See https://github.com/golang/go/issues/38776.)
As a consequence, we end up converting many strings to []byte.
Wrapping a bufio.Writer around the hash writer lets us
avoid these conversions by using WriteString.
Using a bufio.Writer is, perhaps surprisingly, almost as cheap as using unsafe.
The reason is that the sha256 writer does internal buffering,
but doesn't do any when handed larger writers.
Using a bufio.Writer merely shifts the data copying from one buffer
to a different one.
Using a concrete type for Print and print cuts 10% off of the execution time.
name old time/op new time/op delta
Hash-8 15.3µs ± 0% 11.5µs ± 0% -24.84% (p=0.000 n=10+10)
name old alloc/op new alloc/op delta
Hash-8 2.82kB ± 0% 1.98kB ± 0% -29.57% (p=0.000 n=10+10)
name old allocs/op new allocs/op delta
Hash-8 140 ± 0% 82 ± 0% -41.43% (p=0.000 n=10+10)
Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
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