strings: Index(s, "x") not as optimized as bytes.IndexByte

[bradfitz]

bytes.IndexByte is implemented in assembly:

http://golang.org/pkg/bytes/#IndexByte

The strings package lacks an IndexByte method.  It does have a special case for Index
when len(sep) == 1, but not in assembly:

http://golang.org/src/pkg/strings/strings.go?s=1834:1863#L71

Low priority, but inconsistent. I noticed a couple weeks ago when I was looking at some
profiles.

[robpike]

Comment 1:

Status changed to Accepted.

[rsc]

Comment 2:

Labels changed: added go1.1.

[rsc]

Comment 3:

Labels changed: added size-l.

[bradfitz]

Comment 4:

Also:
runtime.eqstring doesn't use the assembly from bytes/asm_amd64.s

[adg]

Comment 5:

What's the best approach here? Copy the code from bytes, or use unsafe tricks to convert
the string to a []byte and defer to bytes.IndexByte?

[bradfitz]

Comment 6:

Russ was proposing moving some of this shared code into package runtime, and having
bytes, strings, and the runtime use it.

[alberts]

Comment 7:

On the runtime.eqstring topic: I've been dealing with database type app that scans
through lots of strings doing equality comparisons, where depending on some details, the
variability in the string is known to be at the start or at the end.
I believe it would have been very useful to have something like
strings.Equal(s1, s2 string, reverse bool) bool
that calls into some suitable assembler somewhere.
Could probably roll our own, but this seems close to the kind of thing the runtime
should be good at.

[bradfitz]

Comment 8:

That's a pretty gross API for the strings package, or the runtime package.

[rsc]

Comment 9:

Please do not send CLs for this issue. I will take care of it later.

[rsc]

Comment 10:

Labels changed: added go1.1maybe, removed go1.1.

[randall77]

Comment 12:

This issue was updated by revision 3d5daa2.

R=bradfitz, r, khr, dave, remyoudompheng, fullung, minux.ma, ality
CC=golang-dev
https://golang.org/cl/8056043

[bradfitz]

Comment 13:

Labels changed: added optimization.

[bradfitz]

Comment 14:

Labels changed: added performance.

[bradfitz]

Comment 15:

Labels changed: removed optimization.

[bradfitz]

Comment 16:

I opened a related issue #5354 for bytes.Compare.