net: halve the allocs in ParseCIDR by sharing slice backing
Share a slice backing between the host address, network ip and mask.
Add tests to verify that each slice header has len==cap to prevent
introducing new behavior into Go programs. This has a small tradeoff
of allocating a larger slice backing when the address is invalid.
Earlier error detection of invalid prefix length helps balance this
cost and a new benchmark for ParseCIDR helps measure it.
This yields a ~22% speedup for all nil err cidr tests:
name old time/op new time/op delta
ParseCIDR/IPv4-24 9.17µs ± 6% 7.20µs ± 7% -21.47% (p=0.000 n=20+20)
ParseCIDR/IPv6-24 9.02µs ± 6% 6.95µs ± 9% -23.02% (p=0.000 n=20+20)
ParseCIDR/IPv4-24 1.51kB ± 0% 1.55kB ± 0% +2.65% (p=0.000 n=20+20)
ParseCIDR/IPv6-24 1.51kB ± 0% 1.55kB ± 0% +2.65% (p=0.000 n=20+20)
ParseCIDR/IPv4-24 68.0 ± 0% 34.0 ± 0% -50.00% (p=0.000 n=20+20)
ParseCIDR/IPv6-24 68.0 ± 0% 34.0 ± 0% -50.00% (p=0.000 n=20+20)
Including non-nil err cidr tests gains around 25%~:
name old time/op new time/op delta
ParseCIDR/IPv4-24 11.8µs ±11% 8.9µs ± 8% -24.88% (p=0.000 n=20+20)
ParseCIDR/IPv6-24 11.7µs ± 7% 8.7µs ± 5% -25.93% (p=0.000 n=20+20)
ParseCIDR/IPv4-24 1.98kB ± 0% 2.00kB ± 0% +1.21% (p=0.000 n=20+20)
ParseCIDR/IPv6-24 1.98kB ± 0% 2.00kB ± 0% +1.21% (p=0.000 n=20+20)
ParseCIDR/IPv4-24 87.0 ± 0% 48.0 ± 0% -44.83% (p=0.000 n=20+20)
ParseCIDR/IPv6-24 87.0 ± 0% 48.0 ± 0% -44.83% (p=0.000 n=20+20)
Change-Id: I17f33c9049f7875b6ebdfde1f80b386a7aef9b94
GitHub-Last-Rev:
0a031f44b458e2c6465d0e59fb4653e08c44a854
GitHub-Pull-Request: golang/go#26948
Reviewed-on: https://go-review.googlesource.com/c/go/+/129118
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>