src/strings/compare_test.go

// Copyright 2013 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package strings_test

// Derived from bytes/compare_test.go.
// Benchmarks omitted since the underlying implementation is identical.

import (
	"internal/testenv"
	. "strings"
	"testing"
	"unsafe"
)

var compareTests = []struct {
	a, b string
	i    int
}{
	{"", "", 0},
	{"a", "", 1},
	{"", "a", -1},
	{"abc", "abc", 0},
	{"ab", "abc", -1},
	{"abc", "ab", 1},
	{"x", "ab", 1},
	{"ab", "x", -1},
	{"x", "a", 1},
	{"b", "x", -1},
	// test runtime·memeq's chunked implementation
	{"abcdefgh", "abcdefgh", 0},
	{"abcdefghi", "abcdefghi", 0},
	{"abcdefghi", "abcdefghj", -1},
}

func TestCompare(t *testing.T) {
	for _, tt := range compareTests {
		numShifts := 16
		for offset := 0; offset <= numShifts; offset++ {
			shiftedB := (Repeat("*", offset) + tt.b)[offset:]
			cmp := Compare(tt.a, shiftedB)
			if cmp != tt.i {
				t.Errorf(`Compare(%q, %q), offset %d = %v; want %v`, tt.a, tt.b, offset, cmp, tt.i)
			}
		}
	}
}

func TestCompareIdenticalString(t *testing.T) {
	var s = "Hello Gophers!"
	if Compare(s, s) != 0 {
		t.Error("s != s")
	}
	if Compare(s, s[:1]) != 1 {
		t.Error("s > s[:1] failed")
	}
}

func TestCompareStrings(t *testing.T) {
	// unsafeString converts a []byte to a string with no allocation.
	// The caller must not modify b while the result string is in use.
	unsafeString := func(b []byte) string {
		return unsafe.String(unsafe.SliceData(b), len(b))
	}

	lengths := make([]int, 0) // lengths to test in ascending order
	for i := 0; i <= 128; i++ {
		lengths = append(lengths, i)
	}
	lengths = append(lengths, 256, 512, 1024, 1333, 4095, 4096, 4097)

	if !testing.Short() || testenv.Builder() != "" {
		lengths = append(lengths, 65535, 65536, 65537, 99999)
	}

	n := lengths[len(lengths)-1]
	a := make([]byte, n+1)
	b := make([]byte, n+1)
	lastLen := 0
	for _, len := range lengths {
		// randomish but deterministic data. No 0 or 255.
		for i := 0; i < len; i++ {
			a[i] = byte(1 + 31*i%254)
			b[i] = byte(1 + 31*i%254)
		}
		// data past the end is different
		for i := len; i <= n; i++ {
			a[i] = 8
			b[i] = 9
		}

		sa, sb := unsafeString(a), unsafeString(b)
		cmp := Compare(sa[:len], sb[:len])
		if cmp != 0 {
			t.Errorf(`CompareIdentical(%d) = %d`, len, cmp)
		}
		if len > 0 {
			cmp = Compare(sa[:len-1], sb[:len])
			if cmp != -1 {
				t.Errorf(`CompareAshorter(%d) = %d`, len, cmp)
			}
			cmp = Compare(sa[:len], sb[:len-1])
			if cmp != 1 {
				t.Errorf(`CompareBshorter(%d) = %d`, len, cmp)
			}
		}
		for k := lastLen; k < len; k++ {
			b[k] = a[k] - 1
			cmp = Compare(unsafeString(a[:len]), unsafeString(b[:len]))
			if cmp != 1 {
				t.Errorf(`CompareAbigger(%d,%d) = %d`, len, k, cmp)
			}
			b[k] = a[k] + 1
			cmp = Compare(unsafeString(a[:len]), unsafeString(b[:len]))
			if cmp != -1 {
				t.Errorf(`CompareBbigger(%d,%d) = %d`, len, k, cmp)
			}
			b[k] = a[k]
		}
		lastLen = len
	}
}