Implementing High-Performance Large Language Models from Scratch with C++: In-Depth Analysis of the LLM-From-Abs-Scratch Project

LLM-From-Abs-Scratch is an open-source project maintained by Shoko-official (GitHub link: https://github.com/Shoko-official/LLM-From-Abs-Scratch, released on 2026-06-05). It aims to build high-performance large language models from scratch using C++ without relying on advanced frameworks like PyTorch or TensorFlow. The project focuses on low-level optimization and clear architecture, providing valuable learning resources for understanding the internal mechanisms of LLMs, and it has both performance advantages and educational value.

Performance Advantages

As a compiled language, C++ has significantly higher execution efficiency than Python, making it suitable for the massive matrix operation scenarios of LLMs. It allows fine-grained control over memory allocation, leverages SIMD instruction sets (AVX/AVX-512) for vectorized computation, implements custom CUDA kernels, and enables deep optimization for hardware architectures.

Educational Value

Implementing from scratch allows developers to deeply understand the low-level details of LLMs: the mathematical essence of self-attention mechanisms, the flow of feedforward networks, details of positional encoding, and the role of layer normalization and residual connections. It is an effective way to learn the Transformer architecture and deep learning principles.

Tensor Operation System

The custom tensor library supports multi-dimensional array storage and computation, including matrix multiplication, element-wise operations, broadcasting mechanisms, and automatic differentiation functions required for backpropagation.

Transformer Architecture Implementation

It fully implements the standard Transformer decoder architecture: multi-head attention mechanism (projecting to multiple subspaces, computing weights, then concatenating), feedforward neural network (GELU activation), layer normalization (normalization of sample features), and residual connections (alleviating deep training difficulties).

Tokenizer

It implements a Byte Pair Encoding (BPE) tokenizer, which converts raw text into integer sequences. This is the key first step for LLMs to process natural language.

Learning and Research

It provides a learning platform for computer science students and AI researchers. By reading and modifying the source code, they can deeply understand the design principles of LLMs and lay the foundation for innovative research.

Embedded Deployment

The high-performance and low-resource consumption characteristics of the C++ implementation make it suitable for deploying lightweight LLMs on edge/embedded devices (after optimization, it can run in resource-constrained environments).

Customized Development

It provides maximum flexibility. Enterprises and research institutions can modify the network structure, add attention variants, or integrate proprietary hardware acceleration according to their needs.

LLM-From-Abs-Scratch reflects the open-source community's pursuit of AI transparency. Against the backdrop of closed-source advanced models from major companies, it has important educational and research value. In the future, the project is expected to expand support for more model architecture variants, optimization algorithms, and hardware backends, becoming an important part of the C++ deep learning ecosystem and providing a foundation for developers to learn and innovate.