internal/crc16: first import

This package implements CRC16 checksums for the FTDI USB driver

internal/crc16/crc16.go

+// Copyright 2020 The go-lpc 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 crc16 // import "github.com/go-lpc/mim/internal/crc16"
+
+import (
+	"hash"
+	"io"
+)
+
+// Hash16 is the common interface implemented by all 16-bit hash functions.
+type Hash16 interface {
+	hash.Hash
+	Sum16() uint16
+}
+
+// The size of a CRC-16 checksum in bytes.
+const Size = 2
+
+// Table is a 256-word table representing the polynomial for efficient processing.
+type Table [256]uint16
+
+var (
+	ftdiTable = Table{
+		0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50A5, 0x60C6, 0x70E7, 0x8108,
+		0x9129, 0xA14A, 0xB16B, 0xC18C, 0xD1AD, 0xE1CE, 0xF1EF, 0x1231, 0x0210,
+		0x3273, 0x2252, 0x52B5, 0x4294, 0x72F7, 0x62D6, 0x9339, 0x8318, 0xB37B,
+		0xA35A, 0xD3BD, 0xC39C, 0xF3FF, 0xE3DE, 0x2462, 0x3443, 0x0420, 0x1401,
+		0x64E6, 0x74C7, 0x44A4, 0x5485, 0xA56A, 0xB54B, 0x8528, 0x9509, 0xE5EE,
+		0xF5CF, 0xC5AC, 0xD58D, 0x3653, 0x2672, 0x1611, 0x0630, 0x76D7, 0x66F6,
+		0x5695, 0x46B4, 0xB75B, 0xA77A, 0x9719, 0x8738, 0xF7DF, 0xE7FE, 0xD79D,
+		0xC7BC, 0x48C4, 0x58E5, 0x6886, 0x78A7, 0x0840, 0x1861, 0x2802, 0x3823,
+		0xC9CC, 0xD9ED, 0xE98E, 0xF9AF, 0x8948, 0x9969, 0xA90A, 0xB92B, 0x5AF5,
+		0x4AD4, 0x7AB7, 0x6A96, 0x1A71, 0x0A50, 0x3A33, 0x2A12, 0xDBFD, 0xCBDC,
+		0xFBBF, 0xEB9E, 0x9B79, 0x8B58, 0xBB3B, 0xAB1A, 0x6CA6, 0x7C87, 0x4CE4,
+		0x5CC5, 0x2C22, 0x3C03, 0x0C60, 0x1C41, 0xEDAE, 0xFD8F, 0xCDEC, 0xDDCD,
+		0xAD2A, 0xBD0B, 0x8D68, 0x9D49, 0x7E97, 0x6EB6, 0x5ED5, 0x4EF4, 0x3E13,
+		0x2E32, 0x1E51, 0x0E70, 0xFF9F, 0xEFBE, 0xDFDD, 0xCFFC, 0xBF1B, 0xAF3A,
+		0x9F59, 0x8F78, 0x9188, 0x81A9, 0xB1CA, 0xA1EB, 0xD10C, 0xC12D, 0xF14E,
+		0xE16F, 0x1080, 0x00A1, 0x30C2, 0x20E3, 0x5004, 0x4025, 0x7046, 0x6067,
+		0x83B9, 0x9398, 0xA3FB, 0xB3DA, 0xC33D, 0xD31C, 0xE37F, 0xF35E, 0x02B1,
+		0x1290, 0x22F3, 0x32D2, 0x4235, 0x5214, 0x6277, 0x7256, 0xB5EA, 0xA5CB,
+		0x95A8, 0x8589, 0xF56E, 0xE54F, 0xD52C, 0xC50D, 0x34E2, 0x24C3, 0x14A0,
+		0x0481, 0x7466, 0x6447, 0x5424, 0x4405, 0xA7DB, 0xB7FA, 0x8799, 0x97B8,
+		0xE75F, 0xF77E, 0xC71D, 0xD73C, 0x26D3, 0x36F2, 0x0691, 0x16B0, 0x6657,
+		0x7676, 0x4615, 0x5634, 0xD94C, 0xC96D, 0xF90E, 0xE92F, 0x99C8, 0x89E9,
+		0xB98A, 0xA9AB, 0x5844, 0x4865, 0x7806, 0x6827, 0x18C0, 0x08E1, 0x3882,
+		0x28A3, 0xCB7D, 0xDB5C, 0xEB3F, 0xFB1E, 0x8BF9, 0x9BD8, 0xABBB, 0xBB9A,
+		0x4A75, 0x5A54, 0x6A37, 0x7A16, 0x0AF1, 0x1AD0, 0x2AB3, 0x3A92, 0xFD2E,
+		0xED0F, 0xDD6C, 0xCD4D, 0xBDAA, 0xAD8B, 0x9DE8, 0x8DC9, 0x7C26, 0x6C07,
+		0x5C64, 0x4C45, 0x3CA2, 0x2C83, 0x1CE0, 0x0CC1, 0xEF1F, 0xFF3E, 0xCF5D,
+		0xDF7C, 0xAF9B, 0xBFBA, 0x8FD9, 0x9FF8, 0x6E17, 0x7E36, 0x4E55, 0x5E74,
+		0x2E93, 0x3EB2, 0x0ED1, 0x1EF0,
+	}
+)
+
+type digest struct {
+	crc uint16
+	tab *Table
+}
+
+func (d *digest) Size() int      { return 2 }
+func (d *digest) BlockSize() int { return 1 }
+func (d *digest) Reset()         { d.crc = 0xffff }
+
+func (d *digest) Write(p []byte) (n int, err error) {
+	d.crc = d.update(p)
+	return len(p), nil
+}
+
+func (d *digest) Sum16() uint16 { return d.crc }
+
+func (d *digest) Sum(in []byte) []byte {
+	s := d.Sum16()
+	return append(in, byte(s>>8), byte(s))
+}
+
+// update returns the result of adding the bytes in data to the crc.
+func (d *digest) update(data []byte) uint16 {
+	for _, v := range data {
+		d.crc = (d.crc&0xff)<<8 ^ (*d.tab)[(byte(d.crc>>8)^(v&0xff))&0xff]
+	}
+	return d.crc
+}
+
+// New creates a new hash.Hash16 computing the CRC-16 checksum
+// using the polynomial represented by the Table.
+// Its Sum method will lay the value out in big-endian byte order.
+func New(tab *Table) Hash16 {
+	if tab == nil {
+		tab = &ftdiTable
+	}
+	return &digest{
+		crc: 0xffff,
+		tab: tab,
+	}
+}
+
+var (
+	_ hash.Hash = (*digest)(nil)
+	_ Hash16    = (*digest)(nil)
+	_ io.Writer = (*digest)(nil)
+)

internal/crc16/crc16_test.go

+// Copyright 2020 The go-lpc 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 crc16_test
+
+import (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+	"testing"
+
+	"github.com/go-lpc/mim/internal/crc16"
+)
+
+func TestCRC16(t *testing.T) {
+	for _, tc := range []struct {
+		raw  []byte
+		want uint16
+	}{
+		{
+			raw:  []byte{0x1, 0x2, 0x3, 0x4, 0x5},
+			want: 0x9304,
+		},
+	} {
+		t.Run(fmt.Sprintf("0x%x", tc.want), func(t *testing.T) {
+			crc := crc16.New(nil)
+			if got, want := crc.BlockSize(), 1; got != want {
+				t.Fatalf("invalid crc16 block size: got=%d, want=%d", got, want)
+			}
+
+			crc.Reset()
+
+			_, err := crc.Write(tc.raw)
+			if err != nil {
+				t.Fatalf("could not write crc16 hash: %+v", err)
+			}
+
+			if got, want := crc.Sum16(), tc.want; got != want {
+				t.Fatalf("invalid crc16 checksum: got=0x%x, want=0x%x",
+					got, want,
+				)
+			}
+
+			asBytes := func(v uint16) []byte {
+				buf := make([]byte, crc.Size())
+				binary.BigEndian.PutUint16(buf, v)
+				return buf
+			}
+
+			if got, want := crc.Sum(nil), asBytes(tc.want); !bytes.Equal(got, want) {
+				t.Fatalf("invalid crc16 checksum: got=0x%x, want=0x%x",
+					got, want,
+				)
+			}
+		})
+	}
+}