This repository contains full examples and other associated code from https://en.algorithmica.org/hpc

The book is still unfinished, and my writing process is very slow and non-sequential — sometimes the "idea → code → benchmarks → article" pipeline may take 6 months or even more — so in this repository you can get a preview on a lot of interesting things that I haven't yet properly written up and published.

Things that have improved on the state-of-the-art:

• Many variants of binary search, the fastest one achieving ~15x speedup over std::lower_bound for small arrays (that fit in cache) and ~8x speedup for large arrays (>1e6).
• Argmin at the speed of memory.
• Implementation of the Floyd-Warshall algorithm that is about 50x faster than the naive "for-for-for" algorithm.

Things that match current state-of-the-art:

• A version of a segment tree that can compute prefix sums in ~2ns plus the time of the slowest memory read.
• (✓ published) An implementation of GCD that works 2-3 faster than std::gcd.
• Integer factorization taking ~0.5ms per 60-bit integer.
• An algorithm for parsing series of integers ~2x faster than scanf("%d") does.
• An implementation of BLAS-level matrix multiplication that can be expressed in about 30 lines of C.
• Various efficient hash tables.
• Efficient FFT and Karatsuba algorithm implementations.

Various benchmarks:

• Benchmarks for branching and predication.
• Benchmarks for RAM and CPU cache system.

At the implementation stage:

• Ordered Trees (apply the same technique as with binary searching, but with dynamically-allocated B-tree nodes)
• Range minimum queries (both static and dynamic)
• Filters (Bloom, cuckoo, xor, theoretical minimum)
• Dot product / logistic regression (newton's method, SIMD, quantization)
• Prime number sieves (blocking plus wheel)
• Sorting (speeding up quicksort and mergesort with SIMD and radix sort)
• Writing series of integers (SIMD + fast mod-10)
• Bitmaps (blocking, SIMD)

At the idea stage:

• String searching (SIMD-based strstr and rolling hashing)
• Using SIMD to speed up Pollard's algorithm (naive sqrt-parallelization)
• SIMD-based random number generation and hashing