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strings: add Compare(x, y string) int, for symmetry with bytes.Compare
The implementation is the same assembly (or Go) routine. Change-Id: Ib937c461c24ad2d5be9b692b4eed40d9eb031412 Reviewed-on: https://go-review.googlesource.com/2828 Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
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@ -1431,6 +1431,9 @@ TEXT runtime·cmpstring(SB),NOSPLIT,$0-20
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MOVL AX, ret+16(FP)
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RET
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TEXT strings·Compare(SB),NOSPLIT,$0
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JMP runtime·cmpstring(SB)
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TEXT bytes·Compare(SB),NOSPLIT,$0-28
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MOVL s1+0(FP), SI
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MOVL s1+4(FP), BX
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@ -1364,6 +1364,9 @@ TEXT runtime·cmpstring(SB),NOSPLIT,$0-40
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MOVQ AX, ret+32(FP)
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RET
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TEXT strings·Compare(SB),NOSPLIT,$0
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JMP runtime·cmpstring(SB)
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TEXT bytes·Compare(SB),NOSPLIT,$0-56
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MOVQ s1+0(FP), SI
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MOVQ s1+8(FP), BX
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@ -832,6 +832,9 @@ TEXT runtime·cmpstring(SB),NOSPLIT,$0-20
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MOVL AX, ret+16(FP)
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RET
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TEXT strings·Compare(SB),NOSPLIT,$0
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JMP runtime·cmpstring(SB)
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TEXT bytes·Compare(SB),NOSPLIT,$0-28
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MOVL s1+0(FP), SI
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MOVL s1+4(FP), BX
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@ -10,6 +10,11 @@ package runtime
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import _ "unsafe" // for go:linkname
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//go:linkname strings_Compare strings.Compare
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func strings_Compare(s1, s2 string) int {
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return cmpstring(s1, s2)
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}
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func cmpstring(s1, s2 string) int {
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l := len(s1)
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if len(s2) < l {
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98
src/strings/compare_test.go
Normal file
98
src/strings/compare_test.go
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@ -0,0 +1,98 @@
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// Copyright 2013 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package strings_test
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// Derived from bytes/compare_test.go.
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// Benchmarks omitted since the underlying implementation is identical.
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import (
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. "strings"
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"testing"
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)
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var compareTests = []struct {
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a, b string
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i int
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}{
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{"", "", 0},
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{"a", "", 1},
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{"", "a", -1},
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{"abc", "abc", 0},
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{"ab", "abc", -1},
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{"abc", "ab", 1},
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{"x", "ab", 1},
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{"ab", "x", -1},
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{"x", "a", 1},
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{"b", "x", -1},
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// test runtime·memeq's chunked implementation
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{"abcdefgh", "abcdefgh", 0},
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{"abcdefghi", "abcdefghi", 0},
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{"abcdefghi", "abcdefghj", -1},
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}
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func TestCompare(t *testing.T) {
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for _, tt := range compareTests {
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cmp := Compare(tt.a, tt.b)
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if cmp != tt.i {
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t.Errorf(`Compare(%q, %q) = %v`, tt.a, tt.b, cmp)
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}
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}
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}
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func TestCompareIdenticalString(t *testing.T) {
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var s = "Hello Gophers!"
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if Compare(s, s) != 0 {
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t.Error("s != s")
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}
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if Compare(s, s[:1]) != 1 {
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t.Error("s > s[:1] failed")
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}
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}
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func TestCompareStrings(t *testing.T) {
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n := 128
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a := make([]byte, n+1)
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b := make([]byte, n+1)
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for len := 0; len < 128; len++ {
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// randomish but deterministic data. No 0 or 255.
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for i := 0; i < len; i++ {
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a[i] = byte(1 + 31*i%254)
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b[i] = byte(1 + 31*i%254)
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}
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// data past the end is different
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for i := len; i <= n; i++ {
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a[i] = 8
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b[i] = 9
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}
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cmp := Compare(string(a[:len]), string(b[:len]))
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if cmp != 0 {
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t.Errorf(`CompareIdentical(%d) = %d`, len, cmp)
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}
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if len > 0 {
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cmp = Compare(string(a[:len-1]), string(b[:len]))
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if cmp != -1 {
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t.Errorf(`CompareAshorter(%d) = %d`, len, cmp)
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}
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cmp = Compare(string(a[:len]), string(b[:len-1]))
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if cmp != 1 {
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t.Errorf(`CompareBshorter(%d) = %d`, len, cmp)
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}
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}
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for k := 0; k < len; k++ {
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b[k] = a[k] - 1
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cmp = Compare(string(a[:len]), string(b[:len]))
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if cmp != 1 {
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t.Errorf(`CompareAbigger(%d,%d) = %d`, len, k, cmp)
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}
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b[k] = a[k] + 1
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cmp = Compare(string(a[:len]), string(b[:len]))
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if cmp != -1 {
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t.Errorf(`CompareBbigger(%d,%d) = %d`, len, k, cmp)
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}
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b[k] = a[k]
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}
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}
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}
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@ -6,3 +6,10 @@ package strings
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// IndexByte returns the index of the first instance of c in s, or -1 if c is not present in s.
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func IndexByte(s string, c byte) int // ../runtime/asm_$GOARCH.s
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// Compare returns an integer comparing two strings lexicographically.
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// The result will be 0 if a==b, -1 if a < b, and +1 if a > b.
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//
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// In most cases it is simpler to use the built-in comparison operators
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// ==, <, >, and so on.
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func Compare(a, b string) int // ../runtime/noasm.go or ../runtime/asm_*.s
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