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// Copyright 2009 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 notsha256 implements the NOTSHA256 algorithm,
// a hash defined as bitwise NOT of SHA256.
// It is used in situations where exact fidelity to SHA256 is unnecessary.
// In particular, it is used in the compiler toolchain,
// which cannot depend directly on cgo when GOEXPERIMENT=boringcrypto
// (and in that mode the real sha256 uses cgo).
package notsha256
import (
"encoding/binary"
"hash"
)
// The size of a checksum in bytes.
const Size = 32
// The blocksize in bytes.
const BlockSize = 64
const (
chunk = 64
init0 = 0x6A09E667
init1 = 0xBB67AE85
init2 = 0x3C6EF372
init3 = 0xA54FF53A
init4 = 0x510E527F
init5 = 0x9B05688C
init6 = 0x1F83D9AB
init7 = 0x5BE0CD19
)
// digest represents the partial evaluation of a checksum.
type digest struct {
h [8]uint32
x [chunk]byte
nx int
len uint64
}
func (d *digest) Reset() {
d.h[0] = init0
d.h[1] = init1
d.h[2] = init2
d.h[3] = init3
d.h[4] = init4
d.h[5] = init5
d.h[6] = init6
d.h[7] = init7
d.nx = 0
d.len = 0
}
// New returns a new hash.Hash computing the NOTSHA256 checksum.
// state of the hash.
func New() hash.Hash {
d := new(digest)
d.Reset()
return d
}
func (d *digest) Size() int {
return Size
}
func (d *digest) BlockSize() int { return BlockSize }
func (d *digest) Write(p []byte) (nn int, err error) {
nn = len(p)
d.len += uint64(nn)
if d.nx > 0 {
n := copy(d.x[d.nx:], p)
d.nx += n
if d.nx == chunk {
block(d, d.x[:])
d.nx = 0
}
p = p[n:]
}
if len(p) >= chunk {
n := len(p) &^ (chunk - 1)
block(d, p[:n])
p = p[n:]
}
if len(p) > 0 {
d.nx = copy(d.x[:], p)
}
return
}
func (d *digest) Sum(in []byte) []byte {
// Make a copy of d so that caller can keep writing and summing.
d0 := *d
hash := d0.checkSum()
return append(in, hash[:]...)
}
func (d *digest) checkSum() [Size]byte {
len := d.len
// Padding. Add a 1 bit and 0 bits until 56 bytes mod 64.
var tmp [64]byte
tmp[0] = 0x80
if len%64 < 56 {
d.Write(tmp[0 : 56-len%64])
} else {
d.Write(tmp[0 : 64+56-len%64])
}
// Length in bits.
len <<= 3
binary.BigEndian.PutUint64(tmp[:], len)
d.Write(tmp[0:8])
if d.nx != 0 {
panic("d.nx != 0")
}
var digest [Size]byte
binary.BigEndian.PutUint32(digest[0:], d.h[0]^0xFFFFFFFF)
binary.BigEndian.PutUint32(digest[4:], d.h[1]^0xFFFFFFFF)
binary.BigEndian.PutUint32(digest[8:], d.h[2]^0xFFFFFFFF)
binary.BigEndian.PutUint32(digest[12:], d.h[3]^0xFFFFFFFF)
binary.BigEndian.PutUint32(digest[16:], d.h[4]^0xFFFFFFFF)
binary.BigEndian.PutUint32(digest[20:], d.h[5]^0xFFFFFFFF)
binary.BigEndian.PutUint32(digest[24:], d.h[6]^0xFFFFFFFF)
binary.BigEndian.PutUint32(digest[28:], d.h[7]^0xFFFFFFFF)
return digest
}
// Sum256 returns the SHA256 checksum of the data.
func Sum256(data []byte) [Size]byte {
var d digest
d.Reset()
d.Write(data)
return d.checkSum()
}
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