Fast exact summation using small and large superaccumulators

Interesting article by Radford M. Neal:

I present two new methods for exactly summing a set of floating-point numbers, and then correctly rounding to the nearest floating-point number. Higher accuracy than simple summation (rounding after each addition) is important in many applications, such as finding the sample mean of data.

Optimizing Dijkstra for real-world performance

Another interesting paper:

Our experimental results currently put our prototype implementation at about twice as fast as the Boost implementation of the algorithm on both real-world and generated large graphs. Furthermore, this preliminary implementation was written in only a few weeks, by a single programmer. The fact that such an early prototype compares favorably against Boost, a well-known open source library developed by expert programmers, gives us reason to believe our design for the queue is indeed better suited to the problem at hand, and the favorable time measurements are not a product of any specific implementation technique we employed.

The Influence of Malloc Placement on TSX Hardware Transactional Memory

Interesting paper:

We show that the placement policies of dynamic storage allocators -- such as those found in common "malloc" implementations -- can influence the L1 conflict miss rate in the L1. Conflict misses -- sometimes called mapping misses -- arise because of less than ideal associativity and represent imbalanced distribution of active memory blocks over the set of available L1 indices. Under transactional execution conflict misses may manifest as aborts, representing wasted or futile effort instead of a simple stall as would occur in normal execution mode.

Conversion numbers to binary ASCII representation - new method

Recently I've checked different methods to convert numbers to binary representation, including use of new PDEP instruction from BMI2 extension.

Today I've updated the article with new SWAR version 2, a tricky use of multiplication. The method is not faster, but I like the approach---in certain conditions multiplication can be seen as multi-shift/bit-or instruction. I've already use multiplication in this way to emulate instruction pmovmskb.

Speeding up bit-parallel population count

Nearly 50% faster than naive version for large data sets. Discovered by accident. :)

Github repositories

I've put source code for my two articles at github:

• SSSE3: fast popcount --- repository
• SSE4 string search - modification of Karp-Rabin algorithm --- repository

Repositories contain original code, read: C99, 32-bit for GCC with inline assembly and also new programs in C++11 using intrinsics, tested in 64-bit environment.


BTW the article about popcount has gained popularity, and I hope another crazy idea about hacking MPSADBW will spread all over the world.

SIMD-ized searching in unique constant dictionary

The problem: there is a ordered dictionary containing only unique keys. Dictionary is read only, and keys are 32-bit (SSE) or 64-bit (AVX2). Read more