In a large codebase within Google, there are thousands of uses of:
	ContainsAny|IndexAny|LastIndexAny|Trim|TrimLeft|TrimRight

An analysis of their usage shows that over 97% of them only use character
sets consisting of only ASCII symbols.

Uses of ContainsAny|IndexAny|LastIndexAny:
	 6% are 1   character  (e.g., "\n" or " ")
	58% are 2-4 characters (e.g., "<>" or "\r\n\t ")
	24% are 5-9 characters (e.g., "()[]*^$")
	10% are 10+ characters (e.g., "+-=&|><!(){}[]^\"~*?:\\/ ")
We optimize for ASCII sets, which are commonly used to search for
"control" characters in some string. We don't optimize for the
single character scenario since IndexRune or IndexByte could be used.

Uses of Trim|TrimLeft|TrimRight:
	71% are 1   character  (e.g., "\n" or " ")
	14% are 2   characters (e.g., "\r\n")
	10% are 3-4 characters (e.g., " \t\r\n")
	 5% are 10+ characters (e.g., "0123456789abcdefABCDEF")
We optimize for the single character case with a simple closured function
that only checks for that character's value. We optimize for the medium
and larger sets using a 16-byte bit-map representing a set of ASCII characters.

The benchmarks below have the following suffix name "%d:%d" where the first
number is the length of the input and the second number is the length
of the charset.

== bytes package ==
benchmark                            old ns/op     new ns/op     delta
BenchmarkIndexAnyASCII/1:1-4         5.09          5.23          +2.75%
BenchmarkIndexAnyASCII/1:2-4         5.81          5.85          +0.69%
BenchmarkIndexAnyASCII/1:4-4         7.22          7.50          +3.88%
BenchmarkIndexAnyASCII/1:8-4         11.0          11.1          +0.91%
BenchmarkIndexAnyASCII/1:16-4        17.5          17.8          +1.71%
BenchmarkIndexAnyASCII/16:1-4        36.0          34.0          -5.56%
BenchmarkIndexAnyASCII/16:2-4        46.6          36.5          -21.67%
BenchmarkIndexAnyASCII/16:4-4        78.0          40.4          -48.21%
BenchmarkIndexAnyASCII/16:8-4        136           47.4          -65.15%
BenchmarkIndexAnyASCII/16:16-4       254           61.5          -75.79%
BenchmarkIndexAnyASCII/256:1-4       542           388           -28.41%
BenchmarkIndexAnyASCII/256:2-4       705           382           -45.82%
BenchmarkIndexAnyASCII/256:4-4       1089          386           -64.55%
BenchmarkIndexAnyASCII/256:8-4       1994          394           -80.24%
BenchmarkIndexAnyASCII/256:16-4      3843          411           -89.31%
BenchmarkIndexAnyASCII/4096:1-4      8522          5873          -31.08%
BenchmarkIndexAnyASCII/4096:2-4      11253         5861          -47.92%
BenchmarkIndexAnyASCII/4096:4-4      17824         5883          -66.99%
BenchmarkIndexAnyASCII/4096:8-4      32053         5871          -81.68%
BenchmarkIndexAnyASCII/4096:16-4     60512         5888          -90.27%
BenchmarkTrimASCII/1:1-4             79.5          70.8          -10.94%
BenchmarkTrimASCII/1:2-4             79.0          105           +32.91%
BenchmarkTrimASCII/1:4-4             79.6          109           +36.93%
BenchmarkTrimASCII/1:8-4             78.8          118           +49.75%
BenchmarkTrimASCII/1:16-4            80.2          132           +64.59%
BenchmarkTrimASCII/16:1-4            243           116           -52.26%
BenchmarkTrimASCII/16:2-4            243           171           -29.63%
BenchmarkTrimASCII/16:4-4            243           176           -27.57%
BenchmarkTrimASCII/16:8-4            241           184           -23.65%
BenchmarkTrimASCII/16:16-4           238           199           -16.39%
BenchmarkTrimASCII/256:1-4           2580          840           -67.44%
BenchmarkTrimASCII/256:2-4           2603          1175          -54.86%
BenchmarkTrimASCII/256:4-4           2572          1188          -53.81%
BenchmarkTrimASCII/256:8-4           2550          1191          -53.29%
BenchmarkTrimASCII/256:16-4          2585          1208          -53.27%
BenchmarkTrimASCII/4096:1-4          39773         12181         -69.37%
BenchmarkTrimASCII/4096:2-4          39946         17231         -56.86%
BenchmarkTrimASCII/4096:4-4          39641         17179         -56.66%
BenchmarkTrimASCII/4096:8-4          39835         17175         -56.88%
BenchmarkTrimASCII/4096:16-4         40229         17215         -57.21%

== strings package ==
benchmark                            old ns/op     new ns/op     delta
BenchmarkIndexAnyASCII/1:1-4         5.94          4.97          -16.33%
BenchmarkIndexAnyASCII/1:2-4         5.94          5.55          -6.57%
BenchmarkIndexAnyASCII/1:4-4         7.45          7.21          -3.22%
BenchmarkIndexAnyASCII/1:8-4         10.8          10.6          -1.85%
BenchmarkIndexAnyASCII/1:16-4        17.4          17.2          -1.15%
BenchmarkIndexAnyASCII/16:1-4        36.4          32.2          -11.54%
BenchmarkIndexAnyASCII/16:2-4        49.6          34.6          -30.24%
BenchmarkIndexAnyASCII/16:4-4        77.5          37.9          -51.10%
BenchmarkIndexAnyASCII/16:8-4        138           45.5          -67.03%
BenchmarkIndexAnyASCII/16:16-4       241           59.1          -75.48%
BenchmarkIndexAnyASCII/256:1-4       509           378           -25.74%
BenchmarkIndexAnyASCII/256:2-4       720           381           -47.08%
BenchmarkIndexAnyASCII/256:4-4       1142          384           -66.37%
BenchmarkIndexAnyASCII/256:8-4       1999          391           -80.44%
BenchmarkIndexAnyASCII/256:16-4      3735          403           -89.21%
BenchmarkIndexAnyASCII/4096:1-4      7973          5824          -26.95%
BenchmarkIndexAnyASCII/4096:2-4      11432         5809          -49.19%
BenchmarkIndexAnyASCII/4096:4-4      18327         5819          -68.25%
BenchmarkIndexAnyASCII/4096:8-4      33059         5828          -82.37%
BenchmarkIndexAnyASCII/4096:16-4     59703         5817          -90.26%
BenchmarkTrimASCII/1:1-4             71.9          71.8          -0.14%
BenchmarkTrimASCII/1:2-4             73.3          103           +40.52%
BenchmarkTrimASCII/1:4-4             71.8          106           +47.63%
BenchmarkTrimASCII/1:8-4             71.2          113           +58.71%
BenchmarkTrimASCII/1:16-4            71.6          128           +78.77%
BenchmarkTrimASCII/16:1-4            152           116           -23.68%
BenchmarkTrimASCII/16:2-4            160           168           +5.00%
BenchmarkTrimASCII/16:4-4            172           170           -1.16%
BenchmarkTrimASCII/16:8-4            200           177           -11.50%
BenchmarkTrimASCII/16:16-4           254           193           -24.02%
BenchmarkTrimASCII/256:1-4           1438          864           -39.92%
BenchmarkTrimASCII/256:2-4           1551          1195          -22.95%
BenchmarkTrimASCII/256:4-4           1770          1200          -32.20%
BenchmarkTrimASCII/256:8-4           2195          1216          -44.60%
BenchmarkTrimASCII/256:16-4          3054          1224          -59.92%
BenchmarkTrimASCII/4096:1-4          21726         12557         -42.20%
BenchmarkTrimASCII/4096:2-4          23586         17508         -25.77%
BenchmarkTrimASCII/4096:4-4          26898         17510         -34.90%
BenchmarkTrimASCII/4096:8-4          33714         17595         -47.81%
BenchmarkTrimASCII/4096:16-4         47429         17700         -62.68%

The benchmarks added test the worst case. For IndexAny, that is when the
charset matches none of the input. For Trim, it is when the charset matches
all of the input.

Change-Id: I970874d101a96b33528fc99b165379abe58cf6ea
Reviewed-on: https://go-review.googlesource.com/31593
Run-TryBot: Joe Tsai <thebrokentoaster@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Martin Möhrmann <martisch@uos.de>