big: add Int methods to act on numbered bits.
Speeds up setting individual bits by ~75%, useful
when using big.Int as a bit set.
R=gri, rsc
CC=golang-dev
https://golang.org/cl/4538053
diff --git a/src/pkg/big/nat.go b/src/pkg/big/nat.go
index 4848d42..2fdae9f 100755
--- a/src/pkg/big/nat.go
+++ b/src/pkg/big/nat.go
@@ -773,6 +773,43 @@
}
+func (z nat) setBit(x nat, i uint, b uint) nat {
+ j := int(i / _W)
+ m := Word(1) << (i % _W)
+ n := len(x)
+ switch b {
+ case 0:
+ z = z.make(n)
+ copy(z, x)
+ if j >= n {
+ // no need to grow
+ return z
+ }
+ z[j] &^= m
+ return z.norm()
+ case 1:
+ if j >= n {
+ n = j + 1
+ }
+ z = z.make(n)
+ copy(z, x)
+ z[j] |= m
+ // no need to normalize
+ return z
+ }
+ panic("set bit is not 0 or 1")
+}
+
+
+func (z nat) bit(i uint) uint {
+ j := int(i / _W)
+ if j >= len(z) {
+ return 0
+ }
+ return uint(z[j] >> (i % _W) & 1)
+}
+
+
func (z nat) and(x, y nat) nat {
m := len(x)
n := len(y)
