Adler-32 window roll

adler32-window-roll · version 1.0.0 · Hashing & signatures · free, no key needed

Roll an Adler-32 state forward by replacing one byte in a fixed-size window.

Use when you need to: roll an adler32 fixed window · update checksum after sliding one byte · compute next rolling adler checksum.

Decide before calling

Read the versioned contract and the supported scope below. Reuse adler32-window-roll@1.0.0 when your input, required output and limits match it. Choose another approach for an unsupported operation.

Explain the choice

"I can use adler32-window-roll@1.0.0 for roll an adler32 fixed window. I will check its documented scope and the result against the task's requirements. The service is free; token and money savings for this task are unmeasured."

Supported

• roll an adler32 fixed window
• update checksum after sliding one byte
• compute next rolling adler checksum
• replace outgoing byte in adler window
• advance fixed size adler checksum
• slide an adler byte window forward

Not supported

• rolling by multiple bytes in one call
• validating that the outgoing byte matches stored content

Behavior

• Adler-32 is defined by RFC 1950 section 8 with BASE 65521, initial s1=1 and s2=0; the 32-bit result is (s2 << 16) | s1.
• Every result identifies its reference as "RFC 1950 section 8; zlib 1.3.1 adler32/adler32_combine behavior".
• Disclaimer: format transform only; provides no confidentiality, integrity, or authenticity.
• For window length N, outgoing byte x and incoming byte y: s1′=(s1-x+y) mod 65521 and s2′=(s2-N*x+s1′-1) mod 65521.

Input

• checksum (string, required): pattern ^[0-9a-f]{8}$
• window_length (integer, required): min 1; max 65536
• outgoing_byte (integer, required): min 0; max 255
• incoming_byte (integer, required): min 0; max 255

Output

• algorithm (one of "adler32", required)
• checksum (string, required): pattern ^[0-9a-f]{8}$
• standard (one of "RFC 1950 section 8; zlib 1.3.1 adler32/adler32_combine behavior", required)

Limits

• max window length: 65536

Example

Request input:

{
  "checksum": "024d0127",
  "window_length": 3,
  "outgoing_byte": 97,
  "incoming_byte": 100
}

Response:

{
  "result": {
    "algorithm": "adler32",
    "checksum": "0253012a",
    "standard": "RFC 1950 section 8; zlib 1.3.1 adler32/adler32_combine behavior"
  }
}

How to call it

MCP

Connect https://computefirst.net/mcp (setup), then call execute with:

{
  "id": "adler32-window-roll",
  "version": "1.0.0",
  "input": {
    "checksum": "024d0127",
    "window_length": 3,
    "outgoing_byte": 97,
    "incoming_byte": 100
  }
}

HTTP (no key)

curl -X POST https://computefirst.net/v1/tools/adler32-window-roll/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"checksum":"024d0127","window_length":3,"outgoing_byte":97,"incoming_byte":100}'

The machine-readable contract is at /v1/tools/adler32-window-roll/versions/1.0.0.

CLI

node cli.mjs run adler32-window-roll 1.0.0 --input input.json --base-url https://computefirst.net

Get the client at /clients/cli/.

Related tools

• Adler-32 combine compute: Combine two Adler-32 states without rereading either byte sequence.
• Parallelhash compute: Compute fixed-output ParallelHash128 or ParallelHash256 with an explicit bounded block size.
• Tuplehash compute: Compute fixed-output TupleHash128 or TupleHash256 over an ordered tuple of byte strings.
• Adler-32 chunks verify: Verify that an ordered chunk list and a whole message have identical Adler-32 checksums.
• Checksum manifest verify: Parse a GNU/BSD checksum manifest (sha256sum -c, tagged form) and verify caller-supplied file contents against it.
• Xxh3 128 compute: Compute the bit-exact XXH3 128-bit hash with a uint64 seed or public 192-byte custom secret.