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Add CRC16 CITT, the most common variant.
- Javadoc - Refactor
1 parent cb6edb5 commit e1a0527

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2 files changed

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‎src/main/java/org/apache/commons/codec/digest/CRC16.java‎

Lines changed: 94 additions & 26 deletions
Original file line numberDiff line numberDiff line change
@@ -17,12 +17,16 @@
1717

1818
package org.apache.commons.codec.digest;
1919

20+
import java.util.Objects;
2021
import java.util.function.Supplier;
2122
import java.util.zip.Checksum;
2223

2324
/**
2425
* CRC-16 checksum implementation based on polynomial {@code x<sup>16</spu> + x^15 + x^2 + 1 (0x8005)} and the initial value {@code 0x0000}. This CRC variant is
2526
* also known as CRC-16-MODBUS.
27+
* <p>
28+
* Since there are so many CRC-16 variants, we do not pick a default.
29+
* </p>
2630
*
2731
* @see <a href="https://en.wikipedia.org/wiki/Cyclic_redundancy_check">Cyclic redundancy check</a>
2832
* @see <a href="https://reveng.sourceforge.io/crc-catalogue/16.htm">Catalogue of parametrised CRC algorithms with 16 bits</a>
@@ -37,8 +41,8 @@ public class CRC16 implements Checksum {
3741
*/
3842
public static class Builder implements Supplier<CRC16> {
3943

40-
private int init = DEFAULT_INIT;
41-
private int[] t = T_DEFAULT;
44+
private int init = INIT_DEFAULT;
45+
private int[] table;
4246

4347
/**
4448
* Constructs a new instance.
@@ -69,16 +73,26 @@ public Builder setInit(final int init) {
6973
/**
7074
* Sets the lookup table.
7175
*
72-
* @param t the lookup table, making a clone of the input array.
76+
* @param table the lookup table, making a clone of the input array, must not be null.
7377
* @return {@code this} instance.
7478
*/
75-
public Builder setTable(final int[] t) {
76-
this.t = t != null ? t.clone() : T_DEFAULT;
79+
public Builder setTable(final int[] table) {
80+
return table(Objects.requireNonNull(table, "table").clone());
81+
}
82+
83+
/**
84+
* Sets the lookup table without making a clone.
85+
*
86+
* @param table the lookup table, must not be null.
87+
* @return {@code this} instance.
88+
*/
89+
private Builder table(final int[] table) {
90+
this.table = Objects.requireNonNull(table, "table");
7791
return this;
7892
}
7993
}
8094

81-
private static final int DEFAULT_INIT = 0x0000;
95+
private static final int INIT_DEFAULT = 0x0000;
8296
// @formatter:off
8397
private static final int[] T_MODBUS = {
8498
0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241,
@@ -114,11 +128,49 @@ public Builder setTable(final int[] t) {
114128
0x4400, 0x84C1, 0x8581, 0x4540, 0x8701, 0x47C0, 0x4680, 0x8641,
115129
0x8201, 0x42C0, 0x4380, 0x8341, 0x4100, 0x81C1, 0x8081, 0x4040
116130
};
117-
118-
private static final int[] T_DEFAULT = T_MODBUS;
131+
// @formatter:on
132+
// @formatter:off
133+
private static final int[] T_CCITT = {
134+
0x0000, 0x1189, 0x2312, 0x329B, 0x4624, 0x57AD, 0x6536, 0x74BF,
135+
0x8C48, 0x9DC1, 0xAF5A, 0xBED3, 0xCA6C, 0xDBE5, 0xE97E, 0xF8F7,
136+
0x1081, 0x0108, 0x3393, 0x221A, 0x56A5, 0x472C, 0x75B7, 0x643E,
137+
0x9CC9, 0x8D40, 0xBFDB, 0xAE52, 0xDAED, 0xCB64, 0xF9FF, 0xE876,
138+
0x2102, 0x308B, 0x0210, 0x1399, 0x6726, 0x76AF, 0x4434, 0x55BD,
139+
0xAD4A, 0xBCC3, 0x8E58, 0x9FD1, 0xEB6E, 0xFAE7, 0xC87C, 0xD9F5,
140+
0x3183, 0x200A, 0x1291, 0x0318, 0x77A7, 0x662E, 0x54B5, 0x453C,
141+
0xBDCB, 0xAC42, 0x9ED9, 0x8F50, 0xFBEF, 0xEA66, 0xD8FD, 0xC974,
142+
0x4204, 0x538D, 0x6116, 0x709F, 0x0420, 0x15A9, 0x2732, 0x36BB,
143+
0xCE4C, 0xDFC5, 0xED5E, 0xFCD7, 0x8868, 0x99E1, 0xAB7A, 0xBAF3,
144+
0x5285, 0x430C, 0x7197, 0x601E, 0x14A1, 0x0528, 0x37B3, 0x263A,
145+
0xDECD, 0xCF44, 0xFDDF, 0xEC56, 0x98E9, 0x8960, 0xBBFB, 0xAA72,
146+
0x6306, 0x728F, 0x4014, 0x519D, 0x2522, 0x34AB, 0x0630, 0x17B9,
147+
0xEF4E, 0xFEC7, 0xCC5C, 0xDDD5, 0xA96A, 0xB8E3, 0x8A78, 0x9BF1,
148+
0x7387, 0x620E, 0x5095, 0x411C, 0x35A3, 0x242A, 0x16B1, 0x0738,
149+
0xFFCF, 0xEE46, 0xDCDD, 0xCD54, 0xB9EB, 0xA862, 0x9AF9, 0x8B70,
150+
0x8408, 0x9581, 0xA71A, 0xB693, 0xC22C, 0xD3A5, 0xE13E, 0xF0B7,
151+
0x0840, 0x19C9, 0x2B52, 0x3ADB, 0x4E64, 0x5FED, 0x6D76, 0x7CFF,
152+
0x9489, 0x8500, 0xB79B, 0xA612, 0xD2AD, 0xC324, 0xF1BF, 0xE036,
153+
0x18C1, 0x0948, 0x3BD3, 0x2A5A, 0x5EE5, 0x4F6C, 0x7DF7, 0x6C7E,
154+
0xA50A, 0xB483, 0x8618, 0x9791, 0xE32E, 0xF2A7, 0xC03C, 0xD1B5,
155+
0x2942, 0x38CB, 0x0A50, 0x1BD9, 0x6F66, 0x7EEF, 0x4C74, 0x5DFD,
156+
0xB58B, 0xA402, 0x9699, 0x8710, 0xF3AF, 0xE226, 0xD0BD, 0xC134,
157+
0x39C3, 0x284A, 0x1AD1, 0x0B58, 0x7FE7, 0x6E6E, 0x5CF5, 0x4D7C,
158+
0xC60C, 0xD785, 0xE51E, 0xF497, 0x8028, 0x91A1, 0xA33A, 0xB2B3,
159+
0x4A44, 0x5BCD, 0x6956, 0x78DF, 0x0C60, 0x1DE9, 0x2F72, 0x3EFB,
160+
0xD68D, 0xC704, 0xF59F, 0xE416, 0x90A9, 0x8120, 0xB3BB, 0xA232,
161+
0x5AC5, 0x4B4C, 0x79D7, 0x685E, 0x1CE1, 0x0D68, 0x3FF3, 0x2E7A,
162+
0xE70E, 0xF687, 0xC41C, 0xD595, 0xA12A, 0xB0A3, 0x8238, 0x93B1,
163+
0x6B46, 0x7ACF, 0x4854, 0x59DD, 0x2D62, 0x3CEB, 0x0E70, 0x1FF9,
164+
0xF78F, 0xE606, 0xD49D, 0xC514, 0xB1AB, 0xA022, 0x92B9, 0x8330,
165+
0x7BC7, 0x6A4E, 0x58D5, 0x495C, 0x3DE3, 0x2C6A, 0x1EF1, 0x0F78
166+
};
167+
// @formatter:on
119168

120169
/**
121170
* Creates a new builder.
171+
* <p>
172+
* Since there are so many CRC-16 variants, we do not pick a default.
173+
* </p>
122174
*
123175
* @return a new builder.
124176
*/
@@ -127,45 +179,61 @@ public static Builder builder() {
127179
}
128180

129181
/**
130-
* Creates a new default CRC16.
182+
* Creates a new CRC16-CCITT.
183+
* <p>
184+
* The init value is {@code 0x0000}.
185+
* </p>
131186
*
132-
* @return a new default CRC16.
187+
* @return a new CRC16-CCITT.
133188
*/
134-
public static CRC16 crc16() {
135-
return builder().setInit(DEFAULT_INIT).setTable(T_DEFAULT).get();
189+
public static CRC16 ccitt() {
190+
return builder().setInit(0x0000).table(T_CCITT).get();
136191
}
137192

138193
/**
139-
* Creates a new MODBUS CRC16.
194+
* Gets a copy of the CCITT table.
140195
*
141-
* @return a new MODBUS CRC16.
196+
* @return a copy of the CCITT table.
142197
*/
143-
public static CRC16 modbus() {
144-
return builder().setInit(0xFFFF).setTable(T_MODBUS).get();
198+
public static int[] getCcittTable() {
199+
return T_CCITT.clone();
145200
}
146201

147-
// @formatter:on
148202
/**
149-
* CRC.
203+
* Gets a copy of the MODBUS table.
204+
*
205+
* @return a copy of the MODBUS table.
150206
*/
151-
private int crc;
152-
private final int init;
153-
private final int[] t;
207+
public static int[] getModbusTable() {
208+
return T_MODBUS.clone();
209+
}
154210

155211
/**
156-
* Constructs a new instance.
212+
* Creates a new CRC16-MODBUS.
213+
* <p>
214+
* The init value is {@code 0xFFFF}.
215+
* </p>
216+
*
217+
* @return a new CRC16-MODBUS.
157218
*/
158-
public CRC16() {
159-
this(builder());
219+
public static CRC16 modbus() {
220+
return builder().setInit(0xFFFF).table(T_MODBUS).get();
160221
}
161222

223+
/**
224+
* CRC.
225+
*/
226+
private int crc;
227+
private final int init;
228+
private final int[] table;
229+
162230
/**
163231
* Constructs a new instance.
164232
*/
165233
private CRC16(final Builder builder) {
166234
this.init = builder.init;
167235
this.crc = builder.init;
168-
this.t = builder.t;
236+
this.table = Objects.requireNonNull(builder.table, "table");
169237
}
170238

171239
/**
@@ -196,6 +264,6 @@ public void update(final byte[] b, final int off, final int len) {
196264

197265
@Override
198266
public void update(final int b) {
199-
crc = crc >>> 8 ^ t[(crc ^ b) & 0xff];
267+
crc = crc >>> 8 ^ table[(crc ^ b) & 0xff];
200268
}
201269
}

‎src/test/java/org/apache/commons/codec/digest/CRC16Test.java‎

Lines changed: 42 additions & 11 deletions
Original file line numberDiff line numberDiff line change
@@ -18,6 +18,7 @@
1818
package org.apache.commons.codec.digest;
1919

2020
import static org.junit.jupiter.api.Assertions.assertEquals;
21+
import static org.junit.jupiter.api.Assertions.assertNotSame;
2122

2223
import java.nio.charset.StandardCharsets;
2324
import java.util.zip.Checksum;
@@ -32,20 +33,38 @@ class CRC16Test {
3233
private static final byte[] BYTES_123456789 = "123456789".getBytes(StandardCharsets.US_ASCII);
3334

3435
@Test
35-
void testDefault() {
36-
final Checksum crc16 = CRC16.crc16();
36+
void testDefaultCcitt() {
37+
final Checksum crc16 = CRC16.ccitt();
3738
crc16.update(BYTES_123456789, 0, 9);
38-
assertEquals(0xBB3D, crc16.getValue());
39+
assertEquals(0x2189, crc16.getValue());
3940
crc16.update(BYTES_123456789, 0, 9);
40-
assertEquals(0xED7B, crc16.getValue());
41+
assertEquals(0xE026, crc16.getValue());
4142
crc16.reset();
4243
crc16.update(BYTES_123456789, 0, 9);
43-
assertEquals(0xBB3D, crc16.getValue());
44+
assertEquals(0x2189, crc16.getValue());
45+
}
46+
47+
@Test
48+
void testDefaultModbus() {
49+
final Checksum crc16 = CRC16.modbus();
50+
crc16.update(BYTES_123456789, 0, 9);
51+
assertEquals(0x4B37, crc16.getValue());
52+
crc16.update(BYTES_123456789, 0, 9);
53+
assertEquals(0x090A, crc16.getValue());
54+
crc16.reset();
55+
crc16.update(BYTES_123456789, 0, 9);
56+
assertEquals(0x4B37, crc16.getValue());
57+
}
58+
59+
@Test
60+
void testGetTables() {
61+
assertNotSame(CRC16.getCcittTable(), CRC16.getCcittTable());
62+
assertNotSame(CRC16.getModbusTable(), CRC16.getModbusTable());
4463
}
4564

4665
@Test
4766
void testInit() {
48-
final Checksum crc16 = CRC16.builder().setInit(0xFFFF).get();
67+
final Checksum crc16 = CRC16.builder().setTable(CRC16.getModbusTable()).setInit(0xFFFF).get();
4968
crc16.update(BYTES_123456789, 0, 9);
5069
assertEquals(0x4B37, crc16.getValue());
5170
crc16.update(BYTES_123456789, 0, 9);
@@ -56,8 +75,8 @@ void testInit() {
5675
}
5776

5877
@Test
59-
void testModbus() {
60-
final Checksum crc16 = CRC16.modbus();
78+
void testModbusCustom() {
79+
final Checksum crc16 = CRC16.builder().setTable(CRC16.getModbusTable()).setInit(0xFFFF).get();
6180
crc16.update(BYTES_123456789, 0, 9);
6281
assertEquals(0x4B37, crc16.getValue());
6382
crc16.update(BYTES_123456789, 0, 9);
@@ -69,7 +88,19 @@ void testModbus() {
6988

7089
@Test
7190
void testReset() {
72-
final Checksum crc16 = new CRC16();
91+
final Checksum crc16 = CRC16.modbus();
92+
crc16.update(BYTES_123456789, 0, 9);
93+
assertEquals(0x4B37, crc16.getValue());
94+
crc16.update(BYTES_123456789, 0, 9);
95+
assertEquals(0x090A, crc16.getValue());
96+
crc16.reset();
97+
crc16.update(BYTES_123456789, 0, 9);
98+
assertEquals(0x4B37, crc16.getValue());
99+
}
100+
101+
@Test
102+
void testResetCustomModbus() {
103+
final Checksum crc16 = CRC16.builder().setTable(CRC16.getModbusTable()).setInit(0x0000).get();
73104
crc16.update(BYTES_123456789, 0, 9);
74105
assertEquals(0xBB3D, crc16.getValue());
75106
crc16.update(BYTES_123456789, 0, 9);
@@ -81,14 +112,14 @@ void testReset() {
81112

82113
@Test
83114
void testUpdateArray() {
84-
final Checksum crc16 = new CRC16();
115+
final Checksum crc16 = CRC16.builder().setTable(CRC16.getModbusTable()).setInit(0x0000).get();
85116
crc16.update(BYTES_123456789, 0, 9);
86117
assertEquals(0xBB3D, crc16.getValue());
87118
}
88119

89120
@Test
90121
void testUpdateInt() {
91-
final Checksum crc16 = new CRC16();
122+
final Checksum crc16 = CRC16.builder().setTable(CRC16.getModbusTable()).setInit(0x0000).get();
92123
final byte[] bytes = BYTES_123456789;
93124
for (final byte element : bytes) {
94125
crc16.update(element);

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