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