1 files changed, 141 insertions, 0 deletions
diff --git a/src/cmd/internal/notsha256/sha256.go b/src/cmd/internal/notsha256/sha256.go
new file mode 100644
index 00000000000..080b3449798
--- /dev/null
+++ b/src/cmd/internal/notsha256/sha256.go
@@ -0,0 +1,141 @@
+// 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()
+}