Package com.marksayson.deletionchecker.checksum

Class Checksums

java.lang.Object

com.marksayson.deletionchecker.checksum.Checksums

public final class Checksums
extends Object

Checksum helpers that operate over a region of a buffer without copying it.

Method Summary

Modifier and Type	Method	Description
static long	crc32cWithFieldZeroed(ByteBuffer file, int fieldOffset, int fieldLength)	Computes the CRC32C of file's bytes from index 0 to its limit, as if the fieldLength bytes starting at fieldOffset were zero.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Details

crc32cWithFieldZeroed

public static long crc32cWithFieldZeroed(ByteBuffer file,
 int fieldOffset,
 int fieldLength)

Computes the CRC32C of file's bytes from index 0 to its limit, as if the fieldLength bytes starting at fieldOffset were zero. This is how a file's own checksum field is excluded from the value that will be written into it: the writer hashes with the field zeroed, and verification re-derives the value the same way.

The three segments (before the field, fieldLength zero bytes, after the field) are streamed in place; the file is never copied. file's position and limit are unchanged.

Parameters:

file - a buffer whose [0, limit) range is the complete file

fieldOffset - the index of the first byte to treat as zero

fieldLength - the number of bytes to treat as zero

Returns:

the CRC32C as an unsigned 32-bit value in the low bits of the result