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https://github.com/golang/go
synced 2024-09-04 23:44:16 +00:00
regexp: fix repeat of preferred empty match
In Perl mode, (|a)* should match an empty string at the start of the input. Instead it matches as many a's as possible. Because (|a)+ is handled correctly, matching only an empty string, this leads to the paradox that e* can match more text than e+ (for e = (|a)) and that e+ is sometimes different from ee*. This is a very old bug that ultimately derives from the picture I drew for e* in https://swtch.com/~rsc/regexp/regexp1.html. The picture is correct for longest-match (POSIX) regexps but subtly wrong for preferred-match (Perl) regexps in the case where e has a preferred empty match. Pointed out by Andrew Gallant in private mail. The current code treats e* and e+ as the same structure, with different entry points. In the case of e* the preference list ends up not quite in the right order, in part because the “before e” and “after e” states are the same state. Splitting them apart fixes the preference list, and that can be done by compiling e* as if it were (e+)?. Like with any bug fix, there is a very low chance of breaking a program that accidentally depends on the buggy behavior. RE2, Go, and Rust all have this bug, and we've all agreed to fix it, to keep the implementations in sync. Fixes #46123. Change-Id: I70e742e71e0a23b626593b16ddef3c1e73b413b0 Reviewed-on: https://go-review.googlesource.com/c/go/+/318750 Trust: Russ Cox <rsc@golang.org> Run-TryBot: Russ Cox <rsc@golang.org> Reviewed-by: Rob Pike <r@golang.org> TryBot-Result: Go Bot <gobot@golang.org>
This commit is contained in:
Russ Cox
parent
fd4631e24f
commit
2a61b3c590
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@ -97,6 +97,7 @@ var findTests = []FindTest{
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{`\B`, "xx", build(1, 1, 1)},
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{`\B`, "x y", nil},
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{`\B`, "xx yy", build(2, 1, 1, 4, 4)},
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{`(|a)*`, "aa", build(3, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2)},
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// RE2 tests
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{`[^\S\s]`, "abcd", nil},
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@ -142,7 +142,7 @@ var onePassTests = []struct {
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{`^(?:(a)|(?:a*))$`, false},
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{`^(?:(?:(?:.(?:$))?))$`, true},
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{`^abcd$`, true},
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{`^(?:(?:a{0,})*?)$`, true},
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{`^(?:(?:a{0,})*?)$`, false},
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{`^(?:(?:a+)*)$`, true},
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{`^(?:(?:a|(?:aa)))$`, true},
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{`^(?:[^\s\S])$`, true},
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@ -57,8 +57,9 @@ func (l1 patchList) append(p *Prog, l2 patchList) patchList {
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// A frag represents a compiled program fragment.
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type frag struct {
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i uint32 // index of first instruction
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out patchList // where to record end instruction
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i uint32 // index of first instruction
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out patchList // where to record end instruction
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nullable bool // whether fragment can match empty string
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}
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type compiler struct {
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@ -159,7 +160,7 @@ func (c *compiler) compile(re *Regexp) frag {
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func (c *compiler) inst(op InstOp) frag {
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// TODO: impose length limit
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f := frag{i: uint32(len(c.p.Inst))}
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f := frag{i: uint32(len(c.p.Inst)), nullable: true}
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c.p.Inst = append(c.p.Inst, Inst{Op: op})
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return f
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}
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@ -194,7 +195,7 @@ func (c *compiler) cat(f1, f2 frag) frag {
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// TODO: elide nop
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f1.out.patch(c.p, f2.i)
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return frag{f1.i, f2.out}
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return frag{f1.i, f2.out, f1.nullable && f2.nullable}
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}
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func (c *compiler) alt(f1, f2 frag) frag {
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@ -211,6 +212,7 @@ func (c *compiler) alt(f1, f2 frag) frag {
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i.Out = f1.i
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i.Arg = f2.i
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f.out = f1.out.append(c.p, f2.out)
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f.nullable = f1.nullable || f2.nullable
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return f
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}
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@ -228,7 +230,12 @@ func (c *compiler) quest(f1 frag, nongreedy bool) frag {
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return f
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}
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func (c *compiler) star(f1 frag, nongreedy bool) frag {
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// loop returns the fragment for the main loop of a plus or star.
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// For plus, it can be used after changing the entry to f1.i.
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// For star, it can be used directly when f1 can't match an empty string.
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// (When f1 can match an empty string, f1* must be implemented as (f1+)?
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// to get the priority match order correct.)
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func (c *compiler) loop(f1 frag, nongreedy bool) frag {
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f := c.inst(InstAlt)
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i := &c.p.Inst[f.i]
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if nongreedy {
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@ -242,8 +249,17 @@ func (c *compiler) star(f1 frag, nongreedy bool) frag {
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return f
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}
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func (c *compiler) star(f1 frag, nongreedy bool) frag {
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if f1.nullable {
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// Use (f1+)? to get priority match order correct.
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// See golang.org/issue/46123.
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return c.quest(c.plus(f1, nongreedy), nongreedy)
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}
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return c.loop(f1, nongreedy)
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}
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func (c *compiler) plus(f1 frag, nongreedy bool) frag {
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return frag{f1.i, c.star(f1, nongreedy).out}
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return frag{f1.i, c.loop(f1, nongreedy).out, f1.nullable}
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}
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func (c *compiler) empty(op EmptyOp) frag {
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@ -255,6 +271,7 @@ func (c *compiler) empty(op EmptyOp) frag {
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func (c *compiler) rune(r []rune, flags Flags) frag {
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f := c.inst(InstRune)
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f.nullable = false
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i := &c.p.Inst[f.i]
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i.Rune = r
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flags &= FoldCase // only relevant flag is FoldCase
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@ -88,6 +88,21 @@ var compileTests = []struct {
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1* empty 4 -> 2
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2 anynotnl -> 3
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3 match
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`},
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{"(?:|a)+", ` 0 fail
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1 nop -> 4
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2 rune1 "a" -> 4
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3* alt -> 1, 2
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4 alt -> 3, 5
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5 match
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`},
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{"(?:|a)*", ` 0 fail
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1 nop -> 4
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2 rune1 "a" -> 4
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3 alt -> 1, 2
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4 alt -> 3, 6
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5* alt -> 3, 6
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6 match
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`},
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}
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12
src/regexp/testdata/basic.dat
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12
src/regexp/testdata/basic.dat
vendored
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@ -124,24 +124,20 @@ E ((a)) abc (0,1)(0,1)(0,1)
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E (a)b(c) abc (0,3)(0,1)(2,3)
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E a+b+c aabbabc (4,7)
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E a* aaa (0,3)
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#E (a*)* - (0,0)(0,0)
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E (a*)* - (0,0)(?,?) RE2/Go
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E (a*)* - (0,0)(0,0)
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E (a*)+ - (0,0)(0,0)
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#E (a*|b)* - (0,0)(0,0)
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E (a*|b)* - (0,0)(?,?) RE2/Go
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E (a*|b)* - (0,0)(0,0)
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E (a+|b)* ab (0,2)(1,2)
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E (a+|b)+ ab (0,2)(1,2)
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E (a+|b)? ab (0,1)(0,1)
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BE [^ab]* cde (0,3)
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#E (^)* - (0,0)(0,0)
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E (^)* - (0,0)(?,?) RE2/Go
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E (^)* - (0,0)(0,0)
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BE a* NULL (0,0)
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E ([abc])*d abbbcd (0,6)(4,5)
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E ([abc])*bcd abcd (0,4)(0,1)
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E a|b|c|d|e e (0,1)
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E (a|b|c|d|e)f ef (0,2)(0,1)
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#E ((a*|b))* - (0,0)(0,0)(0,0)
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E ((a*|b))* - (0,0)(?,?)(?,?) RE2/Go
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E ((a*|b))* - (0,0)(0,0)(0,0)
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BE abcd*efg abcdefg (0,7)
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BE ab* xabyabbbz (1,3)
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BE ab* xayabbbz (1,2)
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18
src/regexp/testdata/nullsubexpr.dat
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18
src/regexp/testdata/nullsubexpr.dat
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@ -1,8 +1,7 @@
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NOTE null subexpression matches : 2002-06-06
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E (a*)* a (0,1)(0,1)
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#E SAME x (0,0)(0,0)
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E SAME x (0,0)(?,?) RE2/Go
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E SAME x (0,0)(0,0)
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E SAME aaaaaa (0,6)(0,6)
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E SAME aaaaaax (0,6)(0,6)
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E (a*)+ a (0,1)(0,1)
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@ -19,8 +18,7 @@ E SAME aaaaaa (0,6)(0,6)
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E SAME aaaaaax (0,6)(0,6)
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E ([a]*)* a (0,1)(0,1)
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#E SAME x (0,0)(0,0)
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E SAME x (0,0)(?,?) RE2/Go
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E SAME x (0,0)(0,0)
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E SAME aaaaaa (0,6)(0,6)
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E SAME aaaaaax (0,6)(0,6)
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E ([a]*)+ a (0,1)(0,1)
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@ -28,8 +26,7 @@ E SAME x (0,0)(0,0)
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E SAME aaaaaa (0,6)(0,6)
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E SAME aaaaaax (0,6)(0,6)
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E ([^b]*)* a (0,1)(0,1)
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#E SAME b (0,0)(0,0)
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E SAME b (0,0)(?,?) RE2/Go
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E SAME b (0,0)(0,0)
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E SAME aaaaaa (0,6)(0,6)
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E SAME aaaaaab (0,6)(0,6)
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E ([ab]*)* a (0,1)(0,1)
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@ -41,11 +38,9 @@ E SAME bbbbbb (0,6)(0,6)
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E SAME aaaabcde (0,5)(0,5)
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E ([^a]*)* b (0,1)(0,1)
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E SAME bbbbbb (0,6)(0,6)
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#E SAME aaaaaa (0,0)(0,0)
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E SAME aaaaaa (0,0)(?,?) RE2/Go
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E SAME aaaaaa (0,0)(0,0)
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E ([^ab]*)* ccccxx (0,6)(0,6)
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#E SAME ababab (0,0)(0,0)
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E SAME ababab (0,0)(?,?) RE2/Go
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E SAME ababab (0,0)(0,0)
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E ((z)+|a)* zabcde (0,2)(1,2)
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@ -65,8 +60,7 @@ B \(a*\)*\(x\)\(\1\) axa (0,3)(0,1)(1,2)(2,3)
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B \(a*\)*\(x\)\(\1\)\(x\) axax (0,4)(0,1)(1,2)(2,3)(3,4)
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B \(a*\)*\(x\)\(\1\)\(x\) axxa (0,3)(1,1)(1,2)(2,2)(2,3)
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#E (a*)*(x) x (0,1)(0,0)(0,1)
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E (a*)*(x) x (0,1)(?,?)(0,1) RE2/Go
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E (a*)*(x) x (0,1)(0,0)(0,1)
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E (a*)*(x) ax (0,2)(0,1)(1,2)
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E (a*)*(x) axa (0,2)(0,1)(1,2)
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BIN
src/regexp/testdata/re2-exhaustive.txt.bz2
vendored
BIN
src/regexp/testdata/re2-exhaustive.txt.bz2
vendored
Binary file not shown.
145
src/regexp/testdata/re2-search.txt
vendored
145
src/regexp/testdata/re2-search.txt
vendored
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@ -1,5 +1,5 @@
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# RE2 basic search tests built by make log
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# Thu Sep 8 13:43:43 EDT 2011
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# Wed May 12 12:13:22 EDT 2021
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Regexp.SearchTests
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strings
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""
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@ -227,22 +227,6 @@ regexps
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0-0;0-0;0-0;0-0
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strings
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""
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""
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regexps
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"a*"
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0-0;0-0;0-0;0-0
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0-0;0-0;0-0;0-0
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"^(?:a*)$"
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0-0;0-0;0-0;0-0
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0-0;0-0;0-0;0-0
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"^(?:a*)"
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0-0;0-0;0-0;0-0
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0-0;0-0;0-0;0-0
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"(?:a*)$"
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0-0;0-0;0-0;0-0
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0-0;0-0;0-0;0-0
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strings
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""
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"xabcdx"
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regexps
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"ab|cd"
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@ -3651,6 +3635,86 @@ regexps
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0-1;0-1;0-1;0-1
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strings
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""
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"a"
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regexps
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"a\\C+"
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-;-;-;-
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-;-;-;-
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"^(?:a\\C+)$"
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-;-;-;-
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-;-;-;-
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"^(?:a\\C+)"
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-;-;-;-
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-;-;-;-
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"(?:a\\C+)$"
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-;-;-;-
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-;-;-;-
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strings
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""
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"a"
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regexps
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"a\\C?"
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-;-;-;-
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0-1;0-1;0-1;0-1
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"^(?:a\\C?)$"
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-;-;-;-
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0-1;0-1;0-1;0-1
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"^(?:a\\C?)"
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-;-;-;-
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0-1;0-1;0-1;0-1
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"(?:a\\C?)$"
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-;-;-;-
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0-1;0-1;0-1;0-1
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strings
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""
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"a"
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regexps
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"a\\C*?"
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-;-;-;-
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0-1;0-1;0-1;0-1
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"^(?:a\\C*?)$"
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-;-;-;-
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0-1;0-1;0-1;0-1
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"^(?:a\\C*?)"
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-;-;-;-
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0-1;0-1;0-1;0-1
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"(?:a\\C*?)$"
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-;-;-;-
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0-1;0-1;0-1;0-1
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strings
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""
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"a"
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regexps
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"a\\C+?"
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-;-;-;-
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-;-;-;-
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"^(?:a\\C+?)$"
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-;-;-;-
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-;-;-;-
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"^(?:a\\C+?)"
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-;-;-;-
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-;-;-;-
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"(?:a\\C+?)$"
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-;-;-;-
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-;-;-;-
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strings
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""
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"a"
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regexps
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"a\\C??"
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-;-;-;-
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0-1;0-1;0-1;0-1
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"^(?:a\\C??)$"
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-;-;-;-
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0-1;0-1;0-1;0-1
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"^(?:a\\C??)"
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-;-;-;-
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0-1;0-1;0-1;0-1
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"(?:a\\C??)$"
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-;-;-;-
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0-1;0-1;0-1;0-1
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strings
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""
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"baba"
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regexps
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"a\\C*|ba\\C"
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@ -3666,7 +3730,50 @@ regexps
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-;-;-;-
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-;1-4;-;1-4
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strings
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"abc"
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""
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"Inc."
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regexps
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"a.*?c|a.*?b"
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"\\w*I\\w*"
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-;-;-;-
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-;0-3;-;0-3
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"^(?:\\w*I\\w*)$"
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-;-;-;-
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-;-;-;-
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"^(?:\\w*I\\w*)"
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-;-;-;-
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-;0-3;-;0-3
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"(?:\\w*I\\w*)$"
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-;-;-;-
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-;-;-;-
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strings
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""
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"aaa"
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regexps
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"(?:|a)*"
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0-0;0-0;0-0;0-0
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0-3;0-0;0-3;0-3
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"^(?:(?:|a)*)$"
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0-0;0-0;0-0;0-0
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0-3;0-3;0-3;0-3
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"^(?:(?:|a)*)"
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0-0;0-0;0-0;0-0
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0-3;0-0;0-3;0-3
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"(?:(?:|a)*)$"
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0-0;0-0;0-0;0-0
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0-3;0-3;0-3;0-3
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strings
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""
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"aaa"
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regexps
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"(?:|a)+"
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0-0;0-0;0-0;0-0
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0-3;0-0;0-3;0-3
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"^(?:(?:|a)+)$"
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0-0;0-0;0-0;0-0
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0-3;0-3;0-3;0-3
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"^(?:(?:|a)+)"
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0-0;0-0;0-0;0-0
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0-3;0-0;0-3;0-3
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"(?:(?:|a)+)$"
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0-0;0-0;0-0;0-0
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0-3;0-3;0-3;0-3
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