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Oct 10, 2013

y-cruncher's Digit Viewer

This is the full self-contained source code for y-cruncher's integrated Digit Viewer.
It includes everything including the heavily optimized back-end conversion code.

This Digit Viewer can also be found inside y-cruncher:

Version 1:

Version 1 is the original DigitViewer that's currently in use by y-cruncher v0.7.5. It was replaced and removed in v0.7.6.

Version 2:

Version 2 is a rewrite of the which was launched with y-cruncher v0.7.6.


  • Project: VSS - DigitViewer2/
  • Source: Source/DigitViewer2/
  • Namespace: DigitViewer2

Compile Instructions:


  • Open the Visual Studio project and compile from within the IDE.
  • Visual Studio 2017 is required.
  • Intel Compiler 2018 is required to build 17-Skylake. AVX512 support in Visual Studio is currently too buggy to use.


  • Run VSS - DigitViewer2/ from the directory it is in. It will create a folder Binaries with the three executables.
  • x64 and a sufficiently new version of GCC is required.
  • There is currently no "real" makefile for Linux builds since all development has been done Windows with Visual Studio.

Build Modes:

  • x86 : 00-x86
  • x86 : 04-SSE3
  • x64 : 04-SSE3
  • x64 : 07-Penryn (SSE4.1)
  • x64 : 13-Haswell (AVX2)
  • x64 : 17-Skylake (AVX512-BW)

The x86 modes are not supported in Linux.


  • New namespace: DigitViewer2
  • Classes renamed to, BasicDigitReader/Writer, BasicTextReader/Writer, and BasicYcdSetReader/Writer. The "basic" prepending is because they now operate at a lower level.
  • The "iterator" paradigm has been removed for all digit readers and writers. Instead, the new paradigm is bulk random access which is better suited for high-level parallelism in the future.
  • The automatic buffering that is used to support the iterator paradigm has been removed. Buffering is now explicit.
  • All classes are now thread-safe in anticipation of high-level parallelism in the future.

Because buffering has been removed, the new classes will be harder to use casually in a performant manner. While it's trivial to build a wrapper that re-adds the buffering to support efficient iteration, this is discouraged as processing a large number of digits one-at-a-time is going to be very slow.


  • All computational operations are now fully parallelized.
  • All computational operations are now fully vectorized for everything from SSE2 through AVX512.
  • Faster decompression of decimal digits by means of an integer invariant-multiply method.
  • Faster digit counts by brute-force parallel SIMD histogramming.
  • Cache blocking optimizations to reduce bandwidth consumption.

New Features

  • Digit hashing is now supported for hexadecimal digits as well.
  • Stats tracking is now done automatically for all digit conversion operations even when it is not requested. The performance improvements from parallelism and vectorization have made the cost negligible.
  • Unfinished .ycd files which have not been completely written out are marked with "(incomplete)" in their names.

To-Do's for the Future:

  • Enable drive parallelism. When digits are distributed over multiple storage devices, they can be processed in parallel. This will require reading the storage topology. It will also require an algorithm to do the actual parallelism when given a specific topology.

Compressed File Format:

To date, I've been too lazy to write a document on the compression format and how the .ycd files are laid out. But it should be pretty easy to see from just examining it through a hex viewer.

Two things that might be useful:

  • Base 16 .ycd files are stored as 64-bit integers words with 16 digits per word.
  • Base 10 .ycd files are stored as 64-bit integers words with 19 digits per word.

In both cases, each 8-byte word is little-endian.

y-cruncher has a build dependency on this Digit Viewer. Not just because it embeds the Digit Viewer, but it also uses the DigitWriter classes to output digits at the end of a computation.

So what you are seeing here is actual y-cruncher source code.


y-cruncher's Digit Viewer




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