Revert float pattern for C++.

Fixes #290.

lexers/c/cpp.go

@@ -24,7 +24,8 @@ var CPP = internal.Register(MustNewLexer(
 			{`(u8|u|U)(")`, ByGroups(LiteralStringAffix, LiteralString), Push("string")},
 			{`(L?)(")`, ByGroups(LiteralStringAffix, LiteralString), Push("string")},
 			{`(L?)(')(\\.|\\[0-7]{1,3}|\\x[a-fA-F0-9]{1,2}|[^\\\'\n])(')`, ByGroups(LiteralStringAffix, LiteralStringChar, LiteralStringChar, LiteralStringChar), nil},
-			{`(\.([0-9](?:'?[0-9]+)*)([eE][+-]?([0-9]('?[0-9]+)*))?|([0-9]('?[0-9]+)*)(([eE][+-]?([0-9]('?[0-9]+)*))|\.([0-9]('?[0-9]+)*)?([eE][+-]?([0-9]('?[0-9]+)*))?)|0[xX](\.([0-9A-Fa-f]('?[0-9A-Fa-f]+)*)([pP][-+]?([0-9]('?[0-9]+)*))?|([0-9A-Fa-f]('?[0-9A-Fa-f]+)*)(([pP][-+]?([0-9]('?[0-9]+)*))|\.([0-9A-Fa-f]('?[0-9A-Fa-f]+)*)?([pP][-+]?([0-9]('?[0-9]+)*))?)))[fFLlUu]*`, LiteralNumberFloat, nil},
+			{`(\d+\.\d*|\.\d+|\d+)[eE][+-]?\d+[LlUu]*`, LiteralNumberFloat, nil},
+			{`(\d+\.\d*|\.\d+|\d+[fF])[fF]?`, LiteralNumberFloat, nil},
 			{`0[xX]([0-9A-Fa-f]('?[0-9A-Fa-f]+)*)[LlUu]*`, LiteralNumberHex, nil},
 			{`0('?[0-7]+)+[LlUu]*`, LiteralNumberOct, nil},
 			{`0[Bb][01]('?[01]+)*[LlUu]*`, LiteralNumberBin, nil},

lexers/c/cpp_test.go

@@ -0,0 +1,27 @@
+package c_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/alecthomas/chroma"
+	"github.com/alecthomas/chroma/lexers/c"
+)
+
+func TestIssue290(t *testing.T) {
+	input := `// 64-bit floats have 53 digits of precision, including the whole-number-part.
+double a =     0011111110111001100110011001100110011001100110011001100110011010; // imperfect representation of 0.1
+double b =     0011111111001001100110011001100110011001100110011001100110011010; // imperfect representation of 0.2
+double c =     0011111111010011001100110011001100110011001100110011001100110011; // imperfect representation of 0.3
+double a + b = 0011111111010011001100110011001100110011001100110011001100110100; // Note that this is not quite equal to the "canonical" 0.3!a
+`
+	it, err := c.CPP.Tokenise(nil, input)
+	require.NoError(t, err)
+	for {
+		token := it()
+		if token == chroma.EOF {
+			break
+		}
+	}
+}