Classify bytes with a direct function rather than a map.

BENCHMARK                     BEFORE          AFTER           SPEEDUP (%)
BenchmarkSplit/len_1-12       637      ns/op  614      ns/op  3.6
BenchmarkSplit/len_4-12       722      ns/op  651      ns/op  9.8
BenchmarkSplit/len_16-12      1027     ns/op  766      ns/op  25
BenchmarkSplit/len_64-12      2240     ns/op  1169     ns/op  47
BenchmarkSplit/len_256-12     7581     ns/op  3075     ns/op  59
BenchmarkSplit/len_1024-12    28900    ns/op  10524    ns/op  65
BenchmarkSplit/len_4096-12    111494   ns/op  40101    ns/op  64
BenchmarkSplit/len_16384-12   443554   ns/op  160389   ns/op  63
BenchmarkSplit/len_65536-12   1839388  ns/op  699041   ns/op  62
BenchmarkSplit/len_100739-12  2852095  ns/op  1093299  ns/op  61

1 files changed, 13 insertions, 12 deletions

diff --git a/shell.go b/shell.go
index e244d10..bfb6f8c 100644
--- a/shell.go
+++ b/shell.go
@@ -140,20 +140,21 @@ var update = [...][]struct {
 	},
 }
 
-var byteClass = map[byte]class{
-	' ':  clBreak,
-	'\t': clBreak,
-	'\n': clNewline,
-	'\\': clQuote,
-	'\'': clSingle,
-	'"':  clDouble,
-}
-
 func classOf(b byte) class {
-	if c, ok := byteClass[b]; ok {
-		return c
+	switch b {
+	case ' ', '\t':
+		return clBreak
+	case '\n':
+		return clNewline
+	case '\\':
+		return clQuote
+	case '\'':
+		return clSingle
+	case '"':
+		return clDouble
+	default:
+		return clOther
 	}
-	return clOther
 }
 
 // A Scanner partitions input from a reader into tokens divided on space, tab,