Description
Choose one uniform legal contiguous block start in a finite index domain; positive block length cannot exceed domain size.
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 one uniform legal contiguous block start in a finite index domain; positive block length cannot exceed domain size.
When to use this tool
Use this tool to choose one uniform legal contiguous block start in a finite index domain; positive block length cannot exceed domain size.
How to use the tool and how it works
- Enter length, blockLength, seed using the definitions below.
- Run the operation. Resolve input-format errors before interpreting an output.
- Read result.seed, result.start, result.end, using the stated boundary, ordering, sign and absence conventions.
Draw start uniformly in 0…length−blockLength and return the half-open interval [start,start+blockLength).1
| Input field | Meaning and units | Accepted input |
|---|---|---|
| length | Explicit integer source/sequence length under the bounds stated above. | Finite safe integer satisfying the stated bounds. |
| blockLength | Positive fixed contiguous block size no greater than length. | Finite safe integer satisfying the stated bounds. |
| 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.start | Inclusive selected interval start or original ring-start index. |
| result.end | Exclusive end of the selected fixed-length contiguous interval. |
{
"input": {
"length": 5,
"blockLength": 2,
"seed": "batch56"
},
"output": {
"result": {
"seed": "batch56",
"start": 2,
"end": 4
}
}
}Limitations and assumptions
- length is 1–128 and blockLength 1–length. The block is contiguous without wrapping.
- 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
Similar or alternative tools
- Random Block Order Permutation
Uniform whole-block position permutation preserving internal order and duplicate display labels.
- Random Contiguous Bit Burst Mask
Choose one uniform nonwrapping contiguous positive bit burst start; the mask is left-to-right text, not an encoded integer.