Subset Bitmask Integer Encoder
Encode a bounded unique index subset into an exact nonnegative integer bitmask, with index zero as the least significant bit.
Description
Encode a bounded unique index subset into an exact nonnegative integer bitmask, with index zero as the least significant bit.
Encoding a subset as an integer mask assigns one bit to each universe index.
When to use this tool
Encode a bounded unique index subset into an exact nonnegative integer bitmask, with index zero as the least significant bit.
- Prepare the supplied indexes, size 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 indexes, size. 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.mask. Interpret false, null and empty lists using the distinctions below; they can be valid outputs.
Validate unique in-range indexes after sorting a copy, OR together 1 shifted left by each index and return decimal-text mask.1
| Input field | Meaning and representation | Accepted input |
|---|---|---|
| indexes | indexes. | List of finite numbers; at most 128 entries |
| size | size. | Safe integer |
| Output field | Interpretation |
|---|---|
| result | Object containing the named outputs below. |
| result.mask | The mask value under the stated formula or text convention. |
{
"input": {
"indexes": [
0,
3
],
"size": 4
},
"output": {
"result": {
"mask": "9"
}
}
}Limitations and assumptions
- size is at most 128 and index zero is the least-significant bit. Duplicate indexes are rejected rather than silently collapsed.
- 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
Retain the universe size, subset size and ordering convention with a rank. Use rank/unrank pairs from the same convention and distinguish subset masks from lexicographic indexes.
References
Similar or alternative tools
- Subset Bitmask Integer Decoder
Decode an exact bounded subset mask into ascending least-significant-bit indexes; masks with bits outside the explicit universe are rejected.
- Mixed Radix Digit Encoder
Encode bounded mixed-radix digits most-significant lane first into exact integer text; every radix is positive and every digit must fit.