Random Byte Replacement Position

Description

Choose a uniform supplied byte position and a uniform different replacement byte among 255 alternatives; position and replacement both exposed.

A random construction is defined by its sampling support: positions, permutations, complete tilings, proposal sequences or another explicit set. Uniform choices at one stage do not necessarily make final visible outcomes uniform. A replay seed gives a deterministic sequence; equal values can hide different sampled positions. These tools are for reproducible synthetic examples rather than cryptographic entropy.

Choose a uniform supplied byte position and a uniform different replacement byte among 255 alternatives; position and replacement both exposed.

When to use this tool

Use this tool to choose a uniform supplied byte position and a uniform different replacement byte among 255 alternatives; position and replacement both exposed.

How to use the tool and how it works

Enter bytes, seed using the definitions below.
Run the operation. Resolve input-format errors before interpreting an output.
Read result.seed, result.index, result.replacement, result.bytes, using the stated boundary, ordering, sign and absence conventions.

Choose an input-byte position uniformly. Draw an integer 0–254 and shift it by one when at or above the original byte value, thereby choosing uniformly among the other 255 values. Replace only that position.^[1]

Input field	Meaning and units	Accepted input
bytes	Dense integer byte values 0–255, at most 128 entries.	Dense list of at most 128 finite numbers, under the stated integer/range rules.
seed	Nonblank replay seed, at most 256 UTF-16 code units; an injected source overrides seeded draws.	Text, at most 8,192 UTF-16 code units; narrower grammar/range rules also apply.

Output field	Interpretation
result	Object containing the fields below.
result.seed	Original supplied seed string; injected-source replay additionally requires that source’s state.
result.index	Zero-based selected source position.
result.replacement	Replacement byte guaranteed to differ from the original at index.
result.bytes	Generated/reordered byte values as integers 0–255, with narrower nonzero rules where stated.

json

{
  "input": {
    "bytes": [
      0,
      100
    ],
    "seed": "batch56"
  },
  "output": {
    "result": {
      "seed": "batch56",
      "index": 1,
      "replacement": 252,
      "bytes": [
        0,
        252
      ]
    }
  }
}

Limitations and assumptions

Input is a nonempty byte list of integers 0–255. The resulting block differs at exactly one position without a hardware fault model.
A nonblank seed of at most 256 UTF-16 code units is required. With ordinary use the seed initializes one deterministic advancing source; an application-injected random source takes precedence and the seed alone then cannot replay the result. Uniformity statements assume independent uniform source draws in [0,1). Source calls are bounded and degenerate injected sources can fail a rejection budget. This is not cryptographically secure.
Every declared outer field is required and unknown outer fields are rejected. Strings and JSON text have size limits, lists are bounded to 128 entries, and JSON nesting/node counts are bounded. Tighter operation-specific bounds stated above take precedence.
Ordinary numeric outputs must be finite and within safe-integer magnitude. Exact large lengths/counts use decimal strings. Original record indexes and code-unit positions are zero-based; span ends are exclusive unless stated otherwise.

Alternative or Complementary methods

Choose a generator whose support matches the intended experiment and retain source-position provenance. Use a separate statistically justified process model or cryptographic source where those properties matter.

References

Tool behavior and example: Random Byte Replacement Position — tool.io

Similar or alternative tools

Random Nonzero Padding Byte Block
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Uniform whole-block position permutation preserving internal order and duplicate display labels.