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license: mit
tags:
- pytorch
- safetensors
- threshold-logic
- neuromorphic
- arithmetic
- adder
---
# threshold-carrysave-adder
4-bit carry-save adder (CSA) as threshold circuit. Adds three 4-bit numbers producing a sum and carry vector, with no carry propagation delay.
## Circuit
```
A[3:0] ──┐
B[3:0] ──┼──► CSA ──┬──► S[3:0] (sum)
C[3:0] ──┘ └──► Cout[3:0] (carry)
Final result: A + B + C = S + (Cout << 1)
```
## How It Works
Each bit position computed independently (no ripple):
```
S[i] = A[i] XOR B[i] XOR C[i]
Cout[i] = MAJ(A[i], B[i], C[i])
```
The carry vector is shifted left by 1 before final addition.
## Truth Table (per bit)
| A | B | C | S | Cout |
|---|---|---|---|------|
| 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 1 | 1 | 0 |
| 0 | 1 | 0 | 1 | 0 |
| 0 | 1 | 1 | 0 | 1 |
| 1 | 0 | 0 | 1 | 0 |
| 1 | 0 | 1 | 0 | 1 |
| 1 | 1 | 0 | 0 | 1 |
| 1 | 1 | 1 | 1 | 1 |
## Architecture
| Component | Count | Neurons |
|-----------|-------|---------|
| XOR3 (sum) | 4 | 28 |
| MAJ3 (carry) | 4 | 4 |
**Total: 32 neurons, 256 parameters, 3 layers**
## Applications
CSAs are fundamental building blocks in:
- Fast multipliers (Wallace trees, Dadda trees)
- Multi-operand addition
- DSP circuits
- Reducing 3 operands to 2 without carry propagation
## Usage
```python
from safetensors.torch import load_file
w = load_file('model.safetensors')
# Example: 15 + 15 + 15 = 45
# S = 13 (1101), Cout = 7 (0111)
# Result = 13 + (7 << 1) = 13 + 14 = 27... wait
# Actually: S + 2*Cout = 13 + 14 = 27, but need final adder
# CSA output needs one final ripple-carry add
```
## Files
```
threshold-carrysave-adder/
├── model.safetensors
├── create_safetensors.py
├── config.json
└── README.md
```
## License
MIT
|