It occurred to me that SHA-3 being a cryptographic hash, it is one of those peculiar bits of code that are fully self-testing. Any bug in a cryptographic hash will quickly cascade to a different result, no matter the bug or the input.
This means the ad-hoc-compiler-monkey can be unleashed “safely”, and can be allowed to try “improper changes.”
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A new kernel for SHA-3 (Keccak) cryptographic hashing has been committed to the DWScript repository.
It is almost 3 times faster than the Pascal version, makes use of MMX asm, and involved an “ad hoc compiler”.
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A trivial way to turn a case-sensitive String hash function into a case-insensitive one is to to pass a lower-case (or upper-case) version of the String.
However, in our days of Unicode strings, this is not innocuous…
Following a recent post by A. Bouchez about an optimized CRC32 hash, I took it as an opportunity to re-run a small String Hashing Shootout on the worst hash function collision torture test I know: ZIP codes in UTF-16 (Delphi’s default String format).
In a Google+ comment to my recent article about inlining in XE6, Leif Uneus posted results from Scimark.
It appears that XE6 is about 30% slower than previous versions at least from XE5 to XE for 32bits floating point.
Note that Scimark does not make use of inlining, but does make heavy use of floating-point computations, loops and arrays.
Edit: issue discussed here was reported in QC 124652 (now marked as resolved)
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First noticed by dewresearch, Delphi XE6 introduced a new optimization for inlined functions that return a floating-point value.
Here is an exploration of what was improved… and what was not improved.
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I recently posted abut the new Slim R/W Locks introduced with Vista, and how they were vastly more efficient than TMREWS.
Apparently, they’re also more efficient than Critical Sections…
Here are a few findings on Multi-Read Exclusive-Write Synchronizer from a recent upgrade of DWScript‘s GlobalVar functions.
I ran some comparisons between a plain Critical Section, Delphi’s TMultiReadExclusiveWriteSynchronizer and Windows Slim Reader/Writer Lock, of which an implementation was added to the dwsXPlatform unit.
Here is a small utility I made whose purpose is to flush (empty) the Windows file cache. It can also flush and purge memory working sets, standby and modified lists.
It can be useful to reduce memory usage of a particular VM (on a host with dynamic memory) or for testing and bench-marking purposes.
Delphi offers two ways of enumerating files in a directory and its sub-directories, the first is the classic (and buggy) FindFirst/FindNext, the second is IOUtils TDirectory.GetFiles and not very efficient.
Here is why and how I implemented DWScript‘s dwsXPlatform.CollectFiles, and a tip about getting a small system-wide boost as a bonus.