---
license: mit
tags:
- pytorch
- safetensors
- threshold-logic
- neuromorphic
---

# threshold-popcount8

8-bit population count. Counts the number of 1 bits in an 8-bit input.

## Function

popcount8(a7..a0) = count of 1 bits (0 to 8)

Output is 4 bits: y3y2y1y0 representing count in binary.

## Truth Table (selected rows)

| Input | Count | Output |
|-------|-------|--------|
| 00000000 | 0 | 0000 |
| 00000001 | 1 | 0001 |
| 01010101 | 4 | 0100 |
| 11110000 | 4 | 0100 |
| 11111111 | 8 | 1000 |

## Architecture

- y3 = (sum == 8)
- y2 = (sum >= 4) AND (sum <= 7)
- y1 = ((sum >= 2) AND (sum <= 3)) OR ((sum >= 6) AND (sum <= 7))
- y0 = XOR8 (parity of all 8 bits)

The parity computation uses a tree of XOR gates: XOR pairs, then XOR the results.

## Parameters

| | |
|---|---|
| Inputs | 8 |
| Outputs | 4 |
| Neurons | 31 |
| Layers | 5 |
| Parameters | 177 |
| Magnitude | 163 |

## Usage

```python
from safetensors.torch import load_file
# See create_safetensors.py for full implementation

# popcount8(1,0,1,0,1,0,1,0) = [0,1,0,0] = 4
```

## License

MIT