Segmented iterators can improve the performance of algorithms by allowing efficient processing of contiguous local ranges while handling boundaries at a higher level.

Neoclassical C++: segmented iterators revisited L: https://boostedcpp.net/2026/05/18/neoclassical-c-segmented-iterators-revisited-1/ C: https://news.ycombinator.com/item?id=48236057 posted on 2026.05.22 at 10:06:44 (c=0, p=3)

Neoclassical C++: segmented iterators revisited https://boostedcpp.net/2026/05/18/neoclassical-c-segmented-iterators-revisited-1/ #HackerNews #Neoclassical #C++ #segmented #iterators #C++ #programming #BoostedCpp #software #development

Neoclassical C++: segmented iterators revisited ---- - a day ago | 7 points | 0 comments - URL: https://boostedcpp.net/2026/05/18/neoclassical-c-segmented-iterators-revisited-1/ - Discussions: https://news.ycombinator.com/item?id=48236057 - Summary: This article revisits Matt Austern’s 2000 paper on segmented iterators, an abstraction where iterators expose an outer segment layer and an inner local layer. For segmented containers like `deque`, standard flat iterators incur overhead at block boundaries and prevent auto-vectorization. Segmented iterators enable hierarchical algorithms that process contiguous local ranges—often raw pointers—efficiently while only handling boundaries at the outer level. The author benchmarks experimental segmented algorithms in Boost.Container against flat and `std::` counterparts using `boost::container::deque`. Testing across MSVC, Clang, and GCC shows dramatic speedups for the segmented path, especially on small, trivially comparable types. For example, MSVC 2026 achieves a nearly 6× geomean speedup over the non-segmented fallback, with individual algorithms like `fill` reaching 17× thanks to SIMD vectorization over contiguous blocks. Performance gains vary by compiler: MSVC 2026 and Clang excel without unroll hints, while GCC 16 benefits from them; Clang can regress with forced unrolling. Standard library implementations generally perform comparably to the non-segmented Boost loops. The conclusion is that segmented iterators remain a powerful abstraction that lets modern compilers and hardware realize significant performance gains.