Add benchmarks that compare two ways of checking for
`multihash.IDENTITY` code:
1. `Cid.Prefix().MhType`
2. Decode of `Cid.Hash()`
This benchmark illustrates that using Cid.Prefix is more efficient than
`multihash.Decode`. Users wishing to perform such a check should use
`Cid.Prefix`.
Consider that `Cid.Prefix` is already efficient enough and introducing a
dedicated API for performing this check will likely result in small
gains.
Relates to #133
We allocate once via "make([]byte, len)",
and again when that buffer is converted to a string.
Thankfully, since Go 1.10 we have strings.Builder,
designed specifically for this use case.
In a downstream benchmark in go-car,
which needs to reconstruct many CID values,
we see small but nice gains:
name old time/op new time/op delta
ReadBlocks-16 1.09ms ± 4% 1.06ms ± 5% -3.33% (p=0.007 n=11+11)
name old speed new speed delta
ReadBlocks-16 478MB/s ± 4% 494MB/s ± 5% +3.46% (p=0.007 n=11+11)
name old alloc/op new alloc/op delta
ReadBlocks-16 1.30MB ± 0% 1.25MB ± 0% -3.86% (p=0.000 n=12+12)
name old allocs/op new allocs/op delta
ReadBlocks-16 9.50k ± 0% 8.45k ± 0% -11.05% (p=0.000 n=12+12)
The append+make slice extension idiom works, but note that append uses
the slice's length as its base. We need to append the number of bytes
required for length to reach cidLength, not the capacity.
The added test case panicked before this change, and works now:
--- FAIL: TestReadCidsFromBuffer (0.00s)
panic: runtime error: slice bounds out of range [:73] with capacity 64 [recovered]
panic: runtime error: slice bounds out of range [:73] with capacity 64
goroutine 37 [running]:
testing.tRunner.func1.2({0x570d60, 0xc000016438})
testing/testing.go:1203 +0x24e
testing.tRunner.func1()
testing/testing.go:1206 +0x218
panic({0x570d60, 0xc000016438})
runtime/panic.go:1038 +0x215
github.com/ipfs/go-cid.CidFromReader({0x5b0e20, 0xc000010900})
github.com/ipfs/go-cid/cid.go:803 +0x75f
github.com/ipfs/go-cid.TestReadCidsFromBuffer(0xc00014ba00)
github.com/ipfs/go-cid/cid_test.go:710 +0x625
testing.tRunner(0xc00014ba00, 0x58af38)
testing/testing.go:1253 +0x102
created by testing.(*T).Run
testing/testing.go:1300 +0x35a
exit status 2
FAIL github.com/ipfs/go-cid 0.004s
You can't see it from here, but go-mulithash now uses registry system,
so it's reasonably possible to introduce new hashers, and to use
(some parts of!) go-multihash without bringing in lots of transitive
dependencies.
The main package of go-multihash still brings in everything
transitively that it did before, so go-cid's transitives aren't
shrinking, and no code is changing here... but it's closer.
If we did cut over to the new go-mulithash/core, we could make
many transitive dependencies become optional.
Base36 was introduced mainly for use in DNS, and various user agents
force lowercase, so tests should use that instead.
License: MIT
Signed-off-by: Marcin Rataj <lidel@lidel.org>
