search_test.go

     1  // Copyright 2010 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package sort_test
     6  
     7  import (
     8  	"runtime"
     9  	. "sort"
    10  	stringspkg "strings"
    11  	"testing"
    12  )
    13  
    14  func f(a []int, x int) func(int) bool {
    15  	return func(i int) bool {
    16  		return a[i] >= x
    17  	}
    18  }
    19  
    20  var data = []int{0: -10, 1: -5, 2: 0, 3: 1, 4: 2, 5: 3, 6: 5, 7: 7, 8: 11, 9: 100, 10: 100, 11: 100, 12: 1000, 13: 10000}
    21  
    22  var tests = []struct {
    23  	name string
    24  	n    int
    25  	f    func(int) bool
    26  	i    int
    27  }{
    28  	{"empty", 0, nil, 0},
    29  	{"1 1", 1, func(i int) bool { return i >= 1 }, 1},
    30  	{"1 true", 1, func(i int) bool { return true }, 0},
    31  	{"1 false", 1, func(i int) bool { return false }, 1},
    32  	{"1e9 991", 1e9, func(i int) bool { return i >= 991 }, 991},
    33  	{"1e9 true", 1e9, func(i int) bool { return true }, 0},
    34  	{"1e9 false", 1e9, func(i int) bool { return false }, 1e9},
    35  	{"data -20", len(data), f(data, -20), 0},
    36  	{"data -10", len(data), f(data, -10), 0},
    37  	{"data -9", len(data), f(data, -9), 1},
    38  	{"data -6", len(data), f(data, -6), 1},
    39  	{"data -5", len(data), f(data, -5), 1},
    40  	{"data 3", len(data), f(data, 3), 5},
    41  	{"data 11", len(data), f(data, 11), 8},
    42  	{"data 99", len(data), f(data, 99), 9},
    43  	{"data 100", len(data), f(data, 100), 9},
    44  	{"data 101", len(data), f(data, 101), 12},
    45  	{"data 10000", len(data), f(data, 10000), 13},
    46  	{"data 10001", len(data), f(data, 10001), 14},
    47  	{"descending a", 7, func(i int) bool { return []int{99, 99, 59, 42, 7, 0, -1, -1}[i] <= 7 }, 4},
    48  	{"descending 7", 1e9, func(i int) bool { return 1e9-i <= 7 }, 1e9 - 7},
    49  	{"overflow", 2e9, func(i int) bool { return false }, 2e9},
    50  }
    51  
    52  func TestSearch(t *testing.T) {
    53  	for _, e := range tests {
    54  		i := Search(e.n, e.f)
    55  		if i != e.i {
    56  			t.Errorf("%s: expected index %d; got %d", e.name, e.i, i)
    57  		}
    58  	}
    59  }
    60  
    61  func TestFind(t *testing.T) {
    62  	str1 := []string{"foo"}
    63  	str2 := []string{"ab", "ca"}
    64  	str3 := []string{"mo", "qo", "vo"}
    65  	str4 := []string{"ab", "ad", "ca", "xy"}
    66  
    67  	// slice with repeating elements
    68  	strRepeats := []string{"ba", "ca", "da", "da", "da", "ka", "ma", "ma", "ta"}
    69  
    70  	// slice with all element equal
    71  	strSame := []string{"xx", "xx", "xx"}
    72  
    73  	tests := []struct {
    74  		data      []string
    75  		target    string
    76  		wantPos   int
    77  		wantFound bool
    78  	}{
    79  		{[]string{}, "foo", 0, false},
    80  		{[]string{}, "", 0, false},
    81  
    82  		{str1, "foo", 0, true},
    83  		{str1, "bar", 0, false},
    84  		{str1, "zx", 1, false},
    85  
    86  		{str2, "aa", 0, false},
    87  		{str2, "ab", 0, true},
    88  		{str2, "ad", 1, false},
    89  		{str2, "ca", 1, true},
    90  		{str2, "ra", 2, false},
    91  
    92  		{str3, "bb", 0, false},
    93  		{str3, "mo", 0, true},
    94  		{str3, "nb", 1, false},
    95  		{str3, "qo", 1, true},
    96  		{str3, "tr", 2, false},
    97  		{str3, "vo", 2, true},
    98  		{str3, "xr", 3, false},
    99  
   100  		{str4, "aa", 0, false},
   101  		{str4, "ab", 0, true},
   102  		{str4, "ac", 1, false},
   103  		{str4, "ad", 1, true},
   104  		{str4, "ax", 2, false},
   105  		{str4, "ca", 2, true},
   106  		{str4, "cc", 3, false},
   107  		{str4, "dd", 3, false},
   108  		{str4, "xy", 3, true},
   109  		{str4, "zz", 4, false},
   110  
   111  		{strRepeats, "da", 2, true},
   112  		{strRepeats, "db", 5, false},
   113  		{strRepeats, "ma", 6, true},
   114  		{strRepeats, "mb", 8, false},
   115  
   116  		{strSame, "xx", 0, true},
   117  		{strSame, "ab", 0, false},
   118  		{strSame, "zz", 3, false},
   119  	}
   120  
   121  	for _, tt := range tests {
   122  		t.Run(tt.target, func(t *testing.T) {
   123  			cmp := func(i int) int {
   124  				return stringspkg.Compare(tt.target, tt.data[i])
   125  			}
   126  
   127  			pos, found := Find(len(tt.data), cmp)
   128  			if pos != tt.wantPos || found != tt.wantFound {
   129  				t.Errorf("Find got (%v, %v), want (%v, %v)", pos, found, tt.wantPos, tt.wantFound)
   130  			}
   131  		})
   132  	}
   133  }
   134  
   135  // log2 computes the binary logarithm of x, rounded up to the next integer.
   136  // (log2(0) == 0, log2(1) == 0, log2(2) == 1, log2(3) == 2, etc.)
   137  func log2(x int) int {
   138  	n := 0
   139  	for p := 1; p < x; p += p {
   140  		// p == 2**n
   141  		n++
   142  	}
   143  	// p/2 < x <= p == 2**n
   144  	return n
   145  }
   146  
   147  func TestSearchEfficiency(t *testing.T) {
   148  	n := 100
   149  	step := 1
   150  	for exp := 2; exp < 10; exp++ {
   151  		// n == 10**exp
   152  		// step == 10**(exp-2)
   153  		max := log2(n)
   154  		for x := 0; x < n; x += step {
   155  			count := 0
   156  			i := Search(n, func(i int) bool { count++; return i >= x })
   157  			if i != x {
   158  				t.Errorf("n = %d: expected index %d; got %d", n, x, i)
   159  			}
   160  			if count > max {
   161  				t.Errorf("n = %d, x = %d: expected <= %d calls; got %d", n, x, max, count)
   162  			}
   163  		}
   164  		n *= 10
   165  		step *= 10
   166  	}
   167  }
   168  
   169  // Smoke tests for convenience wrappers - not comprehensive.
   170  
   171  var fdata = []float64{0: -3.14, 1: 0, 2: 1, 3: 2, 4: 1000.7}
   172  var sdata = []string{0: "f", 1: "foo", 2: "foobar", 3: "x"}
   173  
   174  var wrappertests = []struct {
   175  	name   string
   176  	result int
   177  	i      int
   178  }{
   179  	{"SearchInts", SearchInts(data, 11), 8},
   180  	{"SearchFloat64s", SearchFloat64s(fdata, 2.1), 4},
   181  	{"SearchStrings", SearchStrings(sdata, ""), 0},
   182  	{"IntSlice.Search", IntSlice(data).Search(0), 2},
   183  	{"Float64Slice.Search", Float64Slice(fdata).Search(2.0), 3},
   184  	{"StringSlice.Search", StringSlice(sdata).Search("x"), 3},
   185  }
   186  
   187  func TestSearchWrappers(t *testing.T) {
   188  	for _, e := range wrappertests {
   189  		if e.result != e.i {
   190  			t.Errorf("%s: expected index %d; got %d", e.name, e.i, e.result)
   191  		}
   192  	}
   193  }
   194  
   195  func runSearchWrappers() {
   196  	SearchInts(data, 11)
   197  	SearchFloat64s(fdata, 2.1)
   198  	SearchStrings(sdata, "")
   199  	IntSlice(data).Search(0)
   200  	Float64Slice(fdata).Search(2.0)
   201  	StringSlice(sdata).Search("x")
   202  }
   203  
   204  func TestSearchWrappersDontAlloc(t *testing.T) {
   205  	if testing.Short() {
   206  		t.Skip("skipping malloc count in short mode")
   207  	}
   208  	if runtime.GOMAXPROCS(0) > 1 {
   209  		t.Skip("skipping; GOMAXPROCS>1")
   210  	}
   211  	allocs := testing.AllocsPerRun(100, runSearchWrappers)
   212  	if allocs != 0 {
   213  		t.Errorf("expected no allocs for runSearchWrappers, got %v", allocs)
   214  	}
   215  }
   216  
   217  func BenchmarkSearchWrappers(b *testing.B) {
   218  	for i := 0; i < b.N; i++ {
   219  		runSearchWrappers()
   220  	}
   221  }
   222  
   223  // Abstract exhaustive test: all sizes up to 100,
   224  // all possible return values. If there are any small
   225  // corner cases, this test exercises them.
   226  func TestSearchExhaustive(t *testing.T) {
   227  	for size := 0; size <= 100; size++ {
   228  		for targ := 0; targ <= size; targ++ {
   229  			i := Search(size, func(i int) bool { return i >= targ })
   230  			if i != targ {
   231  				t.Errorf("Search(%d, %d) = %d", size, targ, i)
   232  			}
   233  		}
   234  	}
   235  }
   236  
   237  // Abstract exhaustive test for Find.
   238  func TestFindExhaustive(t *testing.T) {
   239  	// Test Find for different sequence sizes and search targets.
   240  	// For each size, we have a (unmaterialized) sequence of integers:
   241  	//   2,4...size*2
   242  	// And we're looking for every possible integer between 1 and size*2 + 1.
   243  	for size := 0; size <= 100; size++ {
   244  		for x := 1; x <= size*2+1; x++ {
   245  			var wantFound bool
   246  			var wantPos int
   247  
   248  			cmp := func(i int) int {
   249  				// Encodes the unmaterialized sequence with elem[i] == (i+1)*2
   250  				return x - (i+1)*2
   251  			}
   252  			pos, found := Find(size, cmp)
   253  
   254  			if x%2 == 0 {
   255  				wantPos = x/2 - 1
   256  				wantFound = true
   257  			} else {
   258  				wantPos = x / 2
   259  				wantFound = false
   260  			}
   261  			if found != wantFound || pos != wantPos {
   262  				t.Errorf("Find(%d, %d): got (%v, %v), want (%v, %v)", size, x, pos, found, wantPos, wantFound)
   263  			}
   264  		}
   265  	}
   266  }
   267
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