finish uint128be

uint128be.go

@@ -1,6 +1,44 @@
 package unibase2n
 
-type usgnint128 struct {
+import (
+	"encoding/binary"
+	"math/bits"
+)
+
+type uint128be struct {
 	a uint64
 	b uint64
 }
+
+func readuint128be(b []byte) *uint128be {
+	return &uint128be{
+		a: binary.BigEndian.Uint64(b[:8]),
+		b: binary.BigEndian.Uint64(b[8:16]),
+	}
+}
+
+func (num *uint128be) add(n *uint128be) {
+	var c uint64
+	num.b, c = bits.Add64(num.b, n.b, 0)
+	num.a, _ = bits.Add64(num.a, n.a, c)
+	return
+}
+
+// shr only supports shifting 1 ~ 63 bits
+func (num *uint128be) shr(c uint8) {
+	mask := uint64(1)<<c - 1
+	aout := (num.a & mask) << (64 - c)
+	num.a = num.a >> c
+	num.b = aout | (num.b >> c)
+}
+
+func (num *uint128be) and(n *uint128be) {
+	num.a &= n.a
+	num.b &= n.b
+}
+
+func (num *uint128be) write(b []byte) {
+	binary.BigEndian.PutUint64(b[:8], num.a)
+	binary.BigEndian.PutUint64(b[8:16], num.b)
+	return
+}