strings: fix and reenable amd64 Index for 17-31 byte strings

Fixes #15689

Change-Id: I56d0103738cc35cd5bc5e77a0e0341c0dd55530e
Reviewed-on: https://go-review.googlesource.com/23440
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Ilya Tocar <ilya.tocar@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Nigel Tao <nigeltao@golang.org>

diff --git a/src/runtime/asm_amd64.s b/src/runtime/asm_amd64.s
index e50c44304441de2ab405ff39c445e2b0232ed365..f9932cd4349268d70cf7dea4aa5ae912062d500d 100644 (file)
--- a/src/runtime/asm_amd64.s
+++ b/src/runtime/asm_amd64.s
@@ -1787,7 +1787,7 @@ partial_success9to15:
        JB loop9to15
        JMP fail
 _16_or_more:
-       CMPQ AX, $17
+       CMPQ AX, $16
        JA   _17_to_31
        MOVOU (BP), X1
        LEAQ -15(DI)(DX*1), DX
@@ -1801,7 +1801,6 @@ loop16:
        CMPQ DI,DX
        JB loop16
        JMP fail
-//TODO: the code below is wrong.  Fix it.  See #15679.
 _17_to_31:
        LEAQ 1(DI)(DX*1), DX
        SUBQ AX, DX

diff --git a/src/strings/strings_amd64.go b/src/strings/strings_amd64.go
index 91b29ce358fa6d805d93dcf02a02a16d107bd880..55bf2d2f6fc77a05eb4f3f7dbecbefb121b1c80f 100644 (file)
--- a/src/strings/strings_amd64.go
+++ b/src/strings/strings_amd64.go
@@ -7,7 +7,7 @@ package strings
 // indexShortStr returns the index of the first instance of c in s, or -1 if c is not present in s.
 // indexShortStr requires 2 <= len(c) <= shortStringLen
 func indexShortStr(s, c string) int // ../runtime/asm_$GOARCH.s
-const shortStringLen = 16           // TODO: restore to 31 when #15679 is fixed
+const shortStringLen = 31
 
 // Index returns the index of the first instance of sep in s, or -1 if sep is not present in s.
 func Index(s, sep string) int {

diff --git a/src/strings/strings_test.go b/src/strings/strings_test.go
index 6bd6fb5443d31f72cf24e21d563e4b7c4df3b470..fcef761da798a4fd892634ac366a70100d33f544 100644 (file)
--- a/src/strings/strings_test.go
+++ b/src/strings/strings_test.go
@@ -190,6 +190,43 @@ func TestLastIndexByte(t *testing.T) {
        }
 }
 
+func simpleIndex(s, sep string) int {
+       n := len(sep)
+       for i := n; i <= len(s); i++ {
+               if s[i-n:i] == sep {
+                       return i - n
+               }
+       }
+       return -1
+}
+
+func TestIndexRandom(t *testing.T) {
+       const chars = "abcdefghijklmnopqrstuvwxyz0123456789"
+       for times := 0; times < 10; times++ {
+               for strLen := 5 + rand.Intn(5); strLen < 140; strLen += 10 { // Arbitrary
+                       s1 := make([]byte, strLen)
+                       for i := range s1 {
+                               s1[i] = chars[rand.Intn(len(chars))]
+                       }
+                       s := string(s1)
+                       for i := 0; i < 50; i++ {
+                               begin := rand.Intn(len(s) + 1)
+                               end := begin + rand.Intn(len(s)+1-begin)
+                               sep := s[begin:end]
+                               if i%4 == 0 {
+                                       pos := rand.Intn(len(sep) + 1)
+                                       sep = sep[:pos] + "A" + sep[pos:]
+                               }
+                               want := simpleIndex(s, sep)
+                               res := Index(s, sep)
+                               if res != want {
+                                       t.Errorf("Index(%s,%s) = %d; want %d", s, sep, res, want)
+                               }
+                       }
+               }
+       }
+}
+
 var indexRuneTests = []struct {
        s    string
        rune rune