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The following commit(s) were added to refs/heads/master by this push:
new e1a0527a Add CRC16 CITT, the most common variant.
e1a0527a is described below
commit e1a0527a47f5f83662399b78ad2d247726bd2291
Author: Gary D. Gregory <[email protected]>
AuthorDate: Mon Aug 18 08:39:51 2025 -0400
Add CRC16 CITT, the most common variant.
- Javadoc
- Refactor
---
.../org/apache/commons/codec/digest/CRC16.java | 120 ++++++++++++++++-----
.../org/apache/commons/codec/digest/CRC16Test.java | 53 +++++++--
2 files changed, 136 insertions(+), 37 deletions(-)
diff --git a/src/main/java/org/apache/commons/codec/digest/CRC16.java
b/src/main/java/org/apache/commons/codec/digest/CRC16.java
index 58cbe826..d4cc3766 100644
--- a/src/main/java/org/apache/commons/codec/digest/CRC16.java
+++ b/src/main/java/org/apache/commons/codec/digest/CRC16.java
@@ -17,12 +17,16 @@
package org.apache.commons.codec.digest;
+import java.util.Objects;
import java.util.function.Supplier;
import java.util.zip.Checksum;
/**
* 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
* also known as CRC-16-MODBUS.
+ * <p>
+ * Since there are so many CRC-16 variants, we do not pick a default.
+ * </p>
*
* @see <a href="https://en.wikipedia.org/wiki/Cyclic_redundancy_check";>Cyclic
redundancy check</a>
* @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 {
*/
public static class Builder implements Supplier<CRC16> {
- private int init = DEFAULT_INIT;
- private int[] t = T_DEFAULT;
+ private int init = INIT_DEFAULT;
+ private int[] table;
/**
* Constructs a new instance.
@@ -69,16 +73,26 @@ public class CRC16 implements Checksum {
/**
* Sets the lookup table.
*
- * @param t the lookup table, making a clone of the input array.
+ * @param table the lookup table, making a clone of the input array,
must not be null.
* @return {@code this} instance.
*/
- public Builder setTable(final int[] t) {
- this.t = t != null ? t.clone() : T_DEFAULT;
+ public Builder setTable(final int[] table) {
+ return table(Objects.requireNonNull(table, "table").clone());
+ }
+
+ /**
+ * Sets the lookup table without making a clone.
+ *
+ * @param table the lookup table, must not be null.
+ * @return {@code this} instance.
+ */
+ private Builder table(final int[] table) {
+ this.table = Objects.requireNonNull(table, "table");
return this;
}
}
- private static final int DEFAULT_INIT = 0x0000;
+ private static final int INIT_DEFAULT = 0x0000;
// @formatter:off
private static final int[] T_MODBUS = {
0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241,
@@ -114,11 +128,49 @@ public class CRC16 implements Checksum {
0x4400, 0x84C1, 0x8581, 0x4540, 0x8701, 0x47C0, 0x4680, 0x8641,
0x8201, 0x42C0, 0x4380, 0x8341, 0x4100, 0x81C1, 0x8081, 0x4040
};
-
- private static final int[] T_DEFAULT = T_MODBUS;
+ // @formatter:on
+ // @formatter:off
+ private static final int[] T_CCITT = {
+ 0x0000, 0x1189, 0x2312, 0x329B, 0x4624, 0x57AD, 0x6536, 0x74BF,
+ 0x8C48, 0x9DC1, 0xAF5A, 0xBED3, 0xCA6C, 0xDBE5, 0xE97E, 0xF8F7,
+ 0x1081, 0x0108, 0x3393, 0x221A, 0x56A5, 0x472C, 0x75B7, 0x643E,
+ 0x9CC9, 0x8D40, 0xBFDB, 0xAE52, 0xDAED, 0xCB64, 0xF9FF, 0xE876,
+ 0x2102, 0x308B, 0x0210, 0x1399, 0x6726, 0x76AF, 0x4434, 0x55BD,
+ 0xAD4A, 0xBCC3, 0x8E58, 0x9FD1, 0xEB6E, 0xFAE7, 0xC87C, 0xD9F5,
+ 0x3183, 0x200A, 0x1291, 0x0318, 0x77A7, 0x662E, 0x54B5, 0x453C,
+ 0xBDCB, 0xAC42, 0x9ED9, 0x8F50, 0xFBEF, 0xEA66, 0xD8FD, 0xC974,
+ 0x4204, 0x538D, 0x6116, 0x709F, 0x0420, 0x15A9, 0x2732, 0x36BB,
+ 0xCE4C, 0xDFC5, 0xED5E, 0xFCD7, 0x8868, 0x99E1, 0xAB7A, 0xBAF3,
+ 0x5285, 0x430C, 0x7197, 0x601E, 0x14A1, 0x0528, 0x37B3, 0x263A,
+ 0xDECD, 0xCF44, 0xFDDF, 0xEC56, 0x98E9, 0x8960, 0xBBFB, 0xAA72,
+ 0x6306, 0x728F, 0x4014, 0x519D, 0x2522, 0x34AB, 0x0630, 0x17B9,
+ 0xEF4E, 0xFEC7, 0xCC5C, 0xDDD5, 0xA96A, 0xB8E3, 0x8A78, 0x9BF1,
+ 0x7387, 0x620E, 0x5095, 0x411C, 0x35A3, 0x242A, 0x16B1, 0x0738,
+ 0xFFCF, 0xEE46, 0xDCDD, 0xCD54, 0xB9EB, 0xA862, 0x9AF9, 0x8B70,
+ 0x8408, 0x9581, 0xA71A, 0xB693, 0xC22C, 0xD3A5, 0xE13E, 0xF0B7,
+ 0x0840, 0x19C9, 0x2B52, 0x3ADB, 0x4E64, 0x5FED, 0x6D76, 0x7CFF,
+ 0x9489, 0x8500, 0xB79B, 0xA612, 0xD2AD, 0xC324, 0xF1BF, 0xE036,
+ 0x18C1, 0x0948, 0x3BD3, 0x2A5A, 0x5EE5, 0x4F6C, 0x7DF7, 0x6C7E,
+ 0xA50A, 0xB483, 0x8618, 0x9791, 0xE32E, 0xF2A7, 0xC03C, 0xD1B5,
+ 0x2942, 0x38CB, 0x0A50, 0x1BD9, 0x6F66, 0x7EEF, 0x4C74, 0x5DFD,
+ 0xB58B, 0xA402, 0x9699, 0x8710, 0xF3AF, 0xE226, 0xD0BD, 0xC134,
+ 0x39C3, 0x284A, 0x1AD1, 0x0B58, 0x7FE7, 0x6E6E, 0x5CF5, 0x4D7C,
+ 0xC60C, 0xD785, 0xE51E, 0xF497, 0x8028, 0x91A1, 0xA33A, 0xB2B3,
+ 0x4A44, 0x5BCD, 0x6956, 0x78DF, 0x0C60, 0x1DE9, 0x2F72, 0x3EFB,
+ 0xD68D, 0xC704, 0xF59F, 0xE416, 0x90A9, 0x8120, 0xB3BB, 0xA232,
+ 0x5AC5, 0x4B4C, 0x79D7, 0x685E, 0x1CE1, 0x0D68, 0x3FF3, 0x2E7A,
+ 0xE70E, 0xF687, 0xC41C, 0xD595, 0xA12A, 0xB0A3, 0x8238, 0x93B1,
+ 0x6B46, 0x7ACF, 0x4854, 0x59DD, 0x2D62, 0x3CEB, 0x0E70, 0x1FF9,
+ 0xF78F, 0xE606, 0xD49D, 0xC514, 0xB1AB, 0xA022, 0x92B9, 0x8330,
+ 0x7BC7, 0x6A4E, 0x58D5, 0x495C, 0x3DE3, 0x2C6A, 0x1EF1, 0x0F78
+ };
+ // @formatter:on
/**
* Creates a new builder.
+ * <p>
+ * Since there are so many CRC-16 variants, we do not pick a default.
+ * </p>
*
* @return a new builder.
*/
@@ -127,45 +179,61 @@ public class CRC16 implements Checksum {
}
/**
- * Creates a new default CRC16.
+ * Creates a new CRC16-CCITT.
+ * <p>
+ * The init value is {@code 0x0000}.
+ * </p>
*
- * @return a new default CRC16.
+ * @return a new CRC16-CCITT.
*/
- public static CRC16 crc16() {
- return builder().setInit(DEFAULT_INIT).setTable(T_DEFAULT).get();
+ public static CRC16 ccitt() {
+ return builder().setInit(0x0000).table(T_CCITT).get();
}
/**
- * Creates a new MODBUS CRC16.
+ * Gets a copy of the CCITT table.
*
- * @return a new MODBUS CRC16.
+ * @return a copy of the CCITT table.
*/
- public static CRC16 modbus() {
- return builder().setInit(0xFFFF).setTable(T_MODBUS).get();
+ public static int[] getCcittTable() {
+ return T_CCITT.clone();
}
- // @formatter:on
/**
- * CRC.
+ * Gets a copy of the MODBUS table.
+ *
+ * @return a copy of the MODBUS table.
*/
- private int crc;
- private final int init;
- private final int[] t;
+ public static int[] getModbusTable() {
+ return T_MODBUS.clone();
+ }
/**
- * Constructs a new instance.
+ * Creates a new CRC16-MODBUS.
+ * <p>
+ * The init value is {@code 0xFFFF}.
+ * </p>
+ *
+ * @return a new CRC16-MODBUS.
*/
- public CRC16() {
- this(builder());
+ public static CRC16 modbus() {
+ return builder().setInit(0xFFFF).table(T_MODBUS).get();
}
+ /**
+ * CRC.
+ */
+ private int crc;
+ private final int init;
+ private final int[] table;
+
/**
* Constructs a new instance.
*/
private CRC16(final Builder builder) {
this.init = builder.init;
this.crc = builder.init;
- this.t = builder.t;
+ this.table = Objects.requireNonNull(builder.table, "table");
}
/**
@@ -196,6 +264,6 @@ public class CRC16 implements Checksum {
@Override
public void update(final int b) {
- crc = crc >>> 8 ^ t[(crc ^ b) & 0xff];
+ crc = crc >>> 8 ^ table[(crc ^ b) & 0xff];
}
}
diff --git a/src/test/java/org/apache/commons/codec/digest/CRC16Test.java
b/src/test/java/org/apache/commons/codec/digest/CRC16Test.java
index 3393ead0..fd373efc 100644
--- a/src/test/java/org/apache/commons/codec/digest/CRC16Test.java
+++ b/src/test/java/org/apache/commons/codec/digest/CRC16Test.java
@@ -18,6 +18,7 @@
package org.apache.commons.codec.digest;
import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotSame;
import java.nio.charset.StandardCharsets;
import java.util.zip.Checksum;
@@ -32,20 +33,38 @@ class CRC16Test {
private static final byte[] BYTES_123456789 =
"123456789".getBytes(StandardCharsets.US_ASCII);
@Test
- void testDefault() {
- final Checksum crc16 = CRC16.crc16();
+ void testDefaultCcitt() {
+ final Checksum crc16 = CRC16.ccitt();
crc16.update(BYTES_123456789, 0, 9);
- assertEquals(0xBB3D, crc16.getValue());
+ assertEquals(0x2189, crc16.getValue());
crc16.update(BYTES_123456789, 0, 9);
- assertEquals(0xED7B, crc16.getValue());
+ assertEquals(0xE026, crc16.getValue());
crc16.reset();
crc16.update(BYTES_123456789, 0, 9);
- assertEquals(0xBB3D, crc16.getValue());
+ assertEquals(0x2189, crc16.getValue());
+ }
+
+ @Test
+ void testDefaultModbus() {
+ final Checksum crc16 = CRC16.modbus();
+ crc16.update(BYTES_123456789, 0, 9);
+ assertEquals(0x4B37, crc16.getValue());
+ crc16.update(BYTES_123456789, 0, 9);
+ assertEquals(0x090A, crc16.getValue());
+ crc16.reset();
+ crc16.update(BYTES_123456789, 0, 9);
+ assertEquals(0x4B37, crc16.getValue());
+ }
+
+ @Test
+ void testGetTables() {
+ assertNotSame(CRC16.getCcittTable(), CRC16.getCcittTable());
+ assertNotSame(CRC16.getModbusTable(), CRC16.getModbusTable());
}
@Test
void testInit() {
- final Checksum crc16 = CRC16.builder().setInit(0xFFFF).get();
+ final Checksum crc16 =
CRC16.builder().setTable(CRC16.getModbusTable()).setInit(0xFFFF).get();
crc16.update(BYTES_123456789, 0, 9);
assertEquals(0x4B37, crc16.getValue());
crc16.update(BYTES_123456789, 0, 9);
@@ -56,8 +75,8 @@ class CRC16Test {
}
@Test
- void testModbus() {
- final Checksum crc16 = CRC16.modbus();
+ void testModbusCustom() {
+ final Checksum crc16 =
CRC16.builder().setTable(CRC16.getModbusTable()).setInit(0xFFFF).get();
crc16.update(BYTES_123456789, 0, 9);
assertEquals(0x4B37, crc16.getValue());
crc16.update(BYTES_123456789, 0, 9);
@@ -69,7 +88,19 @@ class CRC16Test {
@Test
void testReset() {
- final Checksum crc16 = new CRC16();
+ final Checksum crc16 = CRC16.modbus();
+ crc16.update(BYTES_123456789, 0, 9);
+ assertEquals(0x4B37, crc16.getValue());
+ crc16.update(BYTES_123456789, 0, 9);
+ assertEquals(0x090A, crc16.getValue());
+ crc16.reset();
+ crc16.update(BYTES_123456789, 0, 9);
+ assertEquals(0x4B37, crc16.getValue());
+ }
+
+ @Test
+ void testResetCustomModbus() {
+ final Checksum crc16 =
CRC16.builder().setTable(CRC16.getModbusTable()).setInit(0x0000).get();
crc16.update(BYTES_123456789, 0, 9);
assertEquals(0xBB3D, crc16.getValue());
crc16.update(BYTES_123456789, 0, 9);
@@ -81,14 +112,14 @@ class CRC16Test {
@Test
void testUpdateArray() {
- final Checksum crc16 = new CRC16();
+ final Checksum crc16 =
CRC16.builder().setTable(CRC16.getModbusTable()).setInit(0x0000).get();
crc16.update(BYTES_123456789, 0, 9);
assertEquals(0xBB3D, crc16.getValue());
}
@Test
void testUpdateInt() {
- final Checksum crc16 = new CRC16();
+ final Checksum crc16 =
CRC16.builder().setTable(CRC16.getModbusTable()).setInit(0x0000).get();
final byte[] bytes = BYTES_123456789;
for (final byte element : bytes) {
crc16.update(element);
