regexp: simplify code for brackets, per rsc suggestion

R=rsc
CC=golang-dev
https://golang.org/cl/3545044

diff --git a/src/pkg/regexp/regexp.go b/src/pkg/regexp/regexp.go
index 1cc48a5394f9aa88a4196d68ecdf21ef00b03ec1..1728c7ec26de0858d77694dd52273071bba55c6b 100644 (file)
--- a/src/pkg/regexp/regexp.go
+++ b/src/pkg/regexp/regexp.go
@@ -98,8 +98,7 @@ const (
        iCharClass        // [a-z] character class
        iAny              // '.' any character including newline
        iNotNL            // [^\n] special case: any character but newline
-       iBra              // '(' parenthesized expression
-       iEbra             // ')'; end of '(' parenthesized expression
+       iBra              // '(' parenthesized expression: 2*braNum for left, 2*braNum+1 for right
        iAlt              // '|' alternation
        iNop              // do nothing; makes it easy to link without patching
 )
@@ -135,9 +134,11 @@ func (i *instr) print() {
        case iNotNL:
                print("notnl")
        case iBra:
-               print("bra", i.braNum)
-       case iEbra:
-               print("ebra", i.braNum)
+               if i.braNum&1 == 0 {
+                       print("bra", i.braNum/2)
+               } else {
+                       print("ebra", i.braNum/2)
+               }
        case iAlt:
                print("alt(", i.left.index, ")")
        case iNop:
@@ -391,12 +392,10 @@ func (p *parser) term() (start, end *instr) {
                }
                p.nlpar--
                p.nextc()
-               bra := &instr{kind: iBra}
+               bra := &instr{kind: iBra, braNum: 2 * nbra}
                p.re.add(bra)
-               ebra := &instr{kind: iEbra}
+               ebra := &instr{kind: iBra, braNum: 2*nbra + 1}
                p.re.add(ebra)
-               bra.braNum = nbra
-               ebra.braNum = nbra
                if start == nil {
                        if end == nil {
                                p.error(ErrInternal)
@@ -709,13 +708,7 @@ func (a *matchArena) addState(s []state, inst *instr, prefixed bool, match *matc
                }
                return s
        case iBra:
-               n := inst.braNum
-               match.m[2*n] = pos
-               s = a.addState(s, inst.next, prefixed, match, pos, end)
-               return s
-       case iEbra:
-               n := inst.braNum
-               match.m[2*n+1] = pos
+               match.m[inst.braNum] = pos
                s = a.addState(s, inst.next, prefixed, match, pos, end)
                return s
        }
@@ -821,7 +814,6 @@ func (re *Regexp) doExecute(str string, bytestr []byte, pos int) []int {
                                        s[out] = arena.addState(s[out], st.inst.next, st.prefixed, st.match, pos, end)
                                }
                        case iBra:
-                       case iEbra:
                        case iAlt:
                        case iEnd:
                                // choose leftmost longest