go.tools/container/intsets: support negative elements in BitString().

(I forgot about this when we added support for negative elements generally.)

We use floating point for negative numbers.  The order of the
output is reversed from the previous (little-endian) behaviour
since it makes for more readable floating point.

LGTM=gri
R=gri
CC=golang-codereviews
https://golang.org/cl/95570043
This commit is contained in:
Alan Donovan 2014-05-20 14:52:50 -04:00
parent c0060eca2c
commit 65906ce503
2 changed files with 47 additions and 14 deletions

View File

@ -698,19 +698,44 @@ func (s *Sparse) String() string {
return buf.String() return buf.String()
} }
// BitString returns the set s as a non-empty string of 1s and 0s. // BitString returns the set as a string of 1s and 0s denoting the sum
// The ith character is 1 if the set contains i. // of the i'th powers of 2, for each i in s. A radix point, always
// preceded by a digit, appears if the sum is non-integral.
//
// Examples:
// {}.BitString() = "0"
// {4,5}.BitString() = "110000"
// {-3}.BitString() = "0.001"
// {-3,0,4,5}.BitString() = "110001.001"
// //
func (s *Sparse) BitString() string { func (s *Sparse) BitString() string {
if s.IsEmpty() { if s.IsEmpty() {
return "0" return "0"
} }
b := make([]byte, s.Max()+1)
min, max := s.Min(), s.Max()
var nbytes int
if max > 0 {
nbytes = max
}
nbytes++ // zero bit
radix := nbytes
if min < 0 {
nbytes += len(".") - min
}
b := make([]byte, nbytes)
for i := range b { for i := range b {
b[i] = '0' b[i] = '0'
} }
if radix < nbytes {
b[radix] = '.'
}
s.forEach(func(x int) { s.forEach(func(x int) {
b[x] = '1' if x >= 0 {
x += len(".")
}
b[radix-x] = '1'
}) })
return string(b) return string(b)
} }

View File

@ -23,9 +23,6 @@ func TestBasics(t *testing.T) {
if s := s.String(); s != "{}" { if s := s.String(); s != "{}" {
t.Errorf("String({}): got %q, want \"{}\"", s) t.Errorf("String({}): got %q, want \"{}\"", s)
} }
if s := s.BitString(); s != "0" {
t.Errorf("BitString({}): got %q, want \"0\"", s)
}
if s.Has(3) { if s.Has(3) {
t.Errorf("Has(3): got true, want false") t.Errorf("Has(3): got true, want false")
} }
@ -421,13 +418,24 @@ func TestIntersectionWith(t *testing.T) {
} }
func TestBitString(t *testing.T) { func TestBitString(t *testing.T) {
for _, test := range []struct {
input []int
want string
}{
{nil, "0"},
{[]int{0}, "1"},
{[]int{0, 4, 5}, "110001"},
{[]int{0, 7, 177}, "1" + strings.Repeat("0", 169) + "10000001"},
{[]int{-3, 0, 4, 5}, "110001.001"},
{[]int{-3}, "0.001"},
} {
var set intsets.Sparse var set intsets.Sparse
set.Insert(0) for _, x := range test.input {
set.Insert(7) set.Insert(x)
set.Insert(177) }
want := "10000001" + strings.Repeat("0", 169) + "1" if got := set.BitString(); got != test.want {
if got := set.BitString(); got != want { t.Errorf("BitString(%s) = %s, want %s", set.String(), got, test.want)
t.Errorf("BitString: got %s, want %s", got, want) }
} }
} }