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Adler-32 checksums are 8 hexadecimal characters. The fast checksum inside every zlib stream.
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Adler-32 digest
The digest appears below in hexadecimal.
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Compute the Adler-32 checksum of any text instantly. Adler-32 is the fast 32-bit checksum used inside zlib, shown as 8 hex characters.
Adler-32 checksums are 8 hexadecimal characters. The fast checksum inside every zlib stream.
The digest appears below in hexadecimal.
Adler-32 keeps two running 16-bit sums modulo the prime 65521: s1 adds each byte, s2 adds each s1. The result is s2 in the high 16 bits and s1 in the low 16 bits. It needs only additions, so it runs noticeably faster than CRC32 on CPUs without CRC instructions, which is why zlib chose it.
Speed costs accuracy: Adler-32 is weaker than CRC32, especially on short inputs, where it can miss some error patterns that CRC32 catches. Zlib accepts the tradeoff because decompression itself validates structure. For standalone integrity checks, prefer CRC32 or SHA-256.