threshold-signbit8

Extract sign bit (MSB) of 8-bit number.

Function

signbit8(a7..a0) = a7

In 2's complement representation:

• Output 0: non-negative (0 to 127)
• Output 1: negative (-128 to -1)

Truth Table (selected)

unsigned	signed	signbit
0	0	0
127	+127	0
128	-128	1
255	-1	1

Architecture

Single neuron extracting MSB:

• Weights: [1, 0, 0, 0, 0, 0, 0, 0]
• Bias: -1

Fires when: a7 - 1 >= 0, i.e., a7 >= 1

Parameters

Inputs	8
Outputs	1
Neurons	1
Layers	1
Parameters	9
Magnitude	2

Usage

from safetensors.torch import load_file
import torch

w = load_file('model.safetensors')

def signbit8(a7, a6, a5, a4, a3, a2, a1, a0):
    inp = torch.tensor([float(a7), float(a6), float(a5), float(a4),
                        float(a3), float(a2), float(a1), float(a0)])
    return int((inp @ w['neuron.weight'].T + w['neuron.bias'] >= 0).item())

print(signbit8(0, 1, 1, 1, 1, 1, 1, 1))  # 0 (value = +127)
print(signbit8(1, 0, 0, 0, 0, 0, 0, 0))  # 1 (value = -128)

License

MIT