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// Copyright 2018 The CUE Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package bits
import (
"fmt"
"math"
"math/big"
"math/bits"
)
// Lsh returns x shifted left by n bits.
func Lsh(x *big.Int, n uint) *big.Int {
var z big.Int
z.Lsh(x, n)
return &z
}
// Rsh returns x shifted right by n bits.
func Rsh(x *big.Int, n uint) *big.Int {
var z big.Int
z.Rsh(x, n)
return &z
}
// At returns the value of the i'th bit of x.
func At(x *big.Int, i uint) (uint, error) {
if i > math.MaxInt32 {
return 0, fmt.Errorf("bit index too large")
}
return x.Bit(int(i)), nil
}
// SetBit returns x with x's i'th bit set to b (0 or 1). That is, if b is 1
// SetBit returns x with its i'th bit set; if b is 0 SetBit returns x with
// its i'th bit cleared.
func Set(x *big.Int, i int, bit uint) *big.Int {
var z big.Int
z.SetBit(x, i, bit)
return &z
}
// And returns the bitwise and of a and b.
func And(a, b *big.Int) *big.Int {
var z big.Int
z.And(a, b)
return &z
}
// Or returns the bitwise or of a and b (a | b in Go).
func Or(a, b *big.Int) *big.Int {
var z big.Int
z.Or(a, b)
return &z
}
// Xor returns the bitwise xor of a and b (a ^ b in Go).
func Xor(a, b *big.Int) *big.Int {
var z big.Int
z.Xor(a, b)
return &z
}
// Clear returns the bitwise and not of a and b (a &^ b in Go).
func Clear(a, b *big.Int) *big.Int {
var z big.Int
z.AndNot(a, b)
return &z
}
// OnesCount returns the number of one bits ("population count") in x.
func OnesCount(x *big.Int) int {
var count int
for _, w := range x.Bits() {
count += bits.OnesCount64(uint64(w))
}
return count
}
// TODO: Reverse, ReverseBytes?
// Not entirely sure what that means for infinite precision.
// Reverse returns the value of x with its bits in reversed order.
// func Reverse(x uint64) uint64 {
// return bits.Reverse64(x)
// }
// // ReverseBytes returns the value of x with its bytes in reversed order.
// func ReverseBytes(x uint64) uint64 {
// return bits.ReverseBytes64(x)
// }
// Len returns the length of the absolute value of x in bits. The bit length
// of 0 is 0.
func Len(x *big.Int) int {
return x.BitLen()
}
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