Checksum Methods

The basic idea is to use a CRC checksum generated using the parameters of a function or procedure. The checksum is an 8-byte figure that requires four letters in hexadecimal notation. If the function interface is modified, so is the checksum. This enables the kernel to deduce that the new version is no longer compatible with the old version.

The checksum is not a mathematically unique sum — (different procedures could be mapped to the same checksum because there are more combinations (in fact, an infinite number) derived from procedure parameters than there are checksums available (namely, 232). In practice, this is not a problem because the likelihood that a function interface has the same checksum after several of its parameters have been changed is low.

Continue reading here: Generating a Checksum

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