Cache lib/interval's small bit-masks
diff --git a/lib/interval/interval.go b/lib/interval/interval.go
index 45f556c..9293423 100644
--- a/lib/interval/interval.go
+++ b/lib/interval/interval.go
@@ -42,15 +42,33 @@
one = big.NewInt(1)
)
+var smallBitMasks = [...]*big.Int{
+ big.NewInt(0x00),
+ big.NewInt(0x01),
+ big.NewInt(0x03),
+ big.NewInt(0x07),
+ big.NewInt(0x0F),
+ big.NewInt(0x1F),
+ big.NewInt(0x3F),
+ big.NewInt(0x7F),
+ big.NewInt(0xFF),
+}
+
// bitMask returns ((1<<n) - 1), where n is the largest of n0 and n1.
func bitMask(n0 int, n1 int) *big.Int {
n := n0
if n < n1 {
n = n1
}
- if n > (1 << 30) {
+ if n < 0 {
+ panic("unreachable")
+ } else if n > (1 << 30) {
panic("interval: input is too large")
}
+
+ if n < len(smallBitMasks) {
+ return smallBitMasks[n]
+ }
z := big.NewInt(1)
z = z.Lsh(z, uint(n))
z = z.Sub(z, one)
