}
+// log2 computes the binary logarithm of x, rounded up to the next integer.
+// (log2(0) == 0, log2(1) == 0, log2(2) == 1, log2(3) == 2, etc.)
+//
+func log2(x int) int {
+ n := 0
+ for p := 1; p < x; p += p {
+ // p == 2**n
+ n++
+ }
+ // p/2 < x <= p == 2**n
+ return n
+}
+
+
+func TestSearchEfficiency(t *testing.T) {
+ n := 100
+ step := 1
+ for exp := 2; exp < 10; exp++ {
+ // n == 10**exp
+ // step == 10**(exp-2)
+ max := log2(n)
+ for x := 0; x < n; x += step {
+ count := 0
+ i := Search(n, func(i int) bool { count++; return i <= x })
+ if i != x {
+ t.Errorf("n = %d: expected index %d; got %d", n, x, i)
+ }
+ if count > max {
+ t.Errorf("n = %d, x = %d: expected <= %d calls; got %d", n, x, max, count)
+ }
+ }
+ n *= 10
+ step *= 10
+ }
+}
+
+
// Smoke tests for convenience wrappers - not comprehensive.
var fdata = []float{0: -3.14, 1: 0, 2: 1, 3: 2, 4: 1000.7}