Checksum Field Insertion Tool
Insert an explicit unsigned exact checksum integer into a bounded byte field with caller-selected byte order; does not recompute checksum coverage.
Description
Insert an explicit unsigned exact checksum integer into a bounded byte field with caller-selected byte order; does not recompute checksum coverage.
Inserting a checksum value replaces one bounded field while preserving all other packet bytes.
When to use this tool
Insert an explicit unsigned exact checksum integer into a bounded byte field with caller-selected byte order; does not recompute checksum coverage.
- Prepare the supplied bytes, start, width, checksum, littleEndian fields for this operation.
- Compare the complete example with the representation used by your own input before carrying the result into another step.
How to use the tool and how it works
- Enter bytes, start, width, checksum, littleEndian. Use the exact text syntax, units and index conventions explained below.
- Run the tool. If input validation fails, correct the supplied fields before interpreting any result.
- Read result.bytes. Interpret false, null and empty lists using the distinctions below; they can be valid outputs.
Validate start and width 1 to 16, require the unsigned checksum to fit that many bytes and encode it in the chosen endian order. Replace exactly that slice in bytes.1
| Input field | Meaning and representation | Accepted input |
|---|---|---|
| bytes | bytes. | List of integers from 0 to 255; at most 128 bytes |
| start | start. | Integer from 0 to bytes.length - width inclusive |
| width | width. | Integer from 1 to 16 inclusive |
| checksum | Exact decimal integer text; keep it quoted in JSON rather than converting through a floating-point number. | Optional leading + or - and 1 to 256 decimal digits; no whitespace |
| littleEndian | Explicit choice for little endian; supply a boolean rather than a text label. | true or false |
| Output field | Interpretation |
|---|---|
| result | Object containing the named outputs below. |
| result.bytes | The bytes list in the ordering and representation described above. |
{
"input": {
"bytes": [
0,
0,
9
],
"start": 0,
"width": 2,
"checksum": "258",
"littleEndian": false
},
"output": {
"result": {
"bytes": [
1,
2,
9
]
}
}
}Limitations and assumptions
- The tool does not calculate the checksum or update dependent packet fields. No input buffer or external packet is mutated.
- All declared input fields are required and unexpected top-level fields are rejected. Numbers must be finite; lists are limited to 128 entries and ordinary text fields to 8,192 UTF-16 code units, with tighter limits where stated.
- JSON text inputs must parse within bounded nesting and size limits. Numeric outputs outside the safe finite range are rejected; large exact integer results use decimal strings. Indexes and half-open spans are zero-based unless a rank is explicitly described as one-based.
Alternative or Complementary methods
Use the complete specified checksum algorithm and independent test vectors when verifying a payload. Field packing, parameter shape and arithmetic agreement are separate checks; none supplies cryptographic authenticity.
References
Similar or alternative tools
- Checksum Field Extractor
Extract a bounded unsigned checksum field from explicit bytes as decimal integer text with caller-selected byte order.
- Checksum Field Zeroing Tool
Zero an explicitly bounded checksum field span in copied frame bytes; coverage and protocol layout remain caller responsibilities.