1 files changed, 172 insertions, 0 deletions
diff --git a/test/maplinear.go b/test/maplinear.go
new file mode 100644
index 000000000..34d091491
--- /dev/null
+++ b/test/maplinear.go
@@ -0,0 +1,172 @@
+// +build darwin linux
+// run
+
+// 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.
+
+// Test that maps don't go quadratic for NaNs and other values.
+
+package main
+
+import (
+	"fmt"
+	"math"
+	"time"
+)
+
+// checkLinear asserts that the running time of f(n) is in O(n).
+// tries is the initial number of iterations.
+func checkLinear(typ string, tries int, f func(n int)) {
+	// Depending on the machine and OS, this test might be too fast
+	// to measure with accurate enough granularity. On failure,
+	// make it run longer, hoping that the timing granularity
+	// is eventually sufficient.
+
+	timeF := func(n int) time.Duration {
+		t1 := time.Now()
+		f(n)
+		return time.Since(t1)
+	}
+
+	t0 := time.Now()
+
+	n := tries
+	fails := 0
+	for {
+		t1 := timeF(n)
+		t2 := timeF(2 * n)
+
+		// should be 2x (linear); allow up to 3x
+		if t2 < 3*t1 {
+			if false {
+				fmt.Println(typ, "\t", time.Since(t0))
+			}
+			return
+		}
+		// If n ops run in under a second and the ratio
+		// doesn't work out, make n bigger, trying to reduce
+		// the effect that a constant amount of overhead has
+		// on the computed ratio.
+		if t1 < 1*time.Second {
+			n *= 2
+			continue
+		}
+		// Once the test runs long enough for n ops,
+		// try to get the right ratio at least once.
+		// If five in a row all fail, give up.
+		if fails++; fails >= 5 {
+			panic(fmt.Sprintf("%s: too slow: %d inserts: %v; %d inserts: %v\n",
+				typ, n, t1, 2*n, t2))
+		}
+	}
+}
+
+type I interface {
+	f()
+}
+
+type C int
+
+func (C) f() {}
+
+func main() {
+	// NaNs. ~31ms on a 1.6GHz Zeon.
+	checkLinear("NaN", 30000, func(n int) {
+		m := map[float64]int{}
+		nan := math.NaN()
+		for i := 0; i < n; i++ {
+			m[nan] = 1
+		}
+		if len(m) != n {
+			panic("wrong size map after nan insertion")
+		}
+	})
+
+	// ~6ms on a 1.6GHz Zeon.
+	checkLinear("eface", 10000, func(n int) {
+		m := map[interface{}]int{}
+		for i := 0; i < n; i++ {
+			m[i] = 1
+		}
+	})
+
+	// ~7ms on a 1.6GHz Zeon.
+	// Regression test for CL 119360043.
+	checkLinear("iface", 10000, func(n int) {
+		m := map[I]int{}
+		for i := 0; i < n; i++ {
+			m[C(i)] = 1
+		}
+	})
+
+	// ~6ms on a 1.6GHz Zeon.
+	checkLinear("int", 10000, func(n int) {
+		m := map[int]int{}
+		for i := 0; i < n; i++ {
+			m[i] = 1
+		}
+	})
+
+	// ~18ms on a 1.6GHz Zeon.
+	checkLinear("string", 10000, func(n int) {
+		m := map[string]int{}
+		for i := 0; i < n; i++ {
+			m[fmt.Sprint(i)] = 1
+		}
+	})
+
+	// ~6ms on a 1.6GHz Zeon.
+	checkLinear("float32", 10000, func(n int) {
+		m := map[float32]int{}
+		for i := 0; i < n; i++ {
+			m[float32(i)] = 1
+		}
+	})
+
+	// ~6ms on a 1.6GHz Zeon.
+	checkLinear("float64", 10000, func(n int) {
+		m := map[float64]int{}
+		for i := 0; i < n; i++ {
+			m[float64(i)] = 1
+		}
+	})
+
+	// ~22ms on a 1.6GHz Zeon.
+	checkLinear("complex64", 10000, func(n int) {
+		m := map[complex64]int{}
+		for i := 0; i < n; i++ {
+			m[complex(float32(i), float32(i))] = 1
+		}
+	})
+
+	// ~32ms on a 1.6GHz Zeon.
+	checkLinear("complex128", 10000, func(n int) {
+		m := map[complex128]int{}
+		for i := 0; i < n; i++ {
+			m[complex(float64(i), float64(i))] = 1
+		}
+	})
+
+	// ~70ms on a 1.6GHz Zeon.
+	// The iterate/delete idiom currently takes expected
+	// O(n lg n) time.  Fortunately, the checkLinear test
+	// leaves enough wiggle room to include n lg n time
+	// (it actually tests for O(n^log_2(3)).
+	// To prevent false positives, average away variation
+	// by doing multiple rounds within a single run.
+	checkLinear("iterdelete", 2500, func(n int) {
+		for round := 0; round < 4; round++ {
+			m := map[int]int{}
+			for i := 0; i < n; i++ {
+				m[i] = i
+			}
+			for i := 0; i < n; i++ {
+				for k := range m {
+					delete(m, k)
+					break
+				}
+			}
+		}
+	})
+}