In another comment of the Curiouser Case, Arnaud Bouchez pointed to an interesting optimization that is use in mORMot‘s UpperCopy255Buf function: a branchless parallel upper case conversion.
At the core of that implementation are the following lines of code
c := src[i]; d := c or _80; dest[i] := c - ((d - _61) and not (d - _7b)) and ((not c) and _80) shr 2;
Ok, it may not be too obvious what happens at first sight. Let’s break it down.
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In a comment to the previous article on a case insensitive hash code, Stefan Glienke pointed to an approach used in Spring4D’s comparers, which is a delightful hack.
Rather than converting the string to a “proper lower case”, it converts the string to an “approximate lower case” using an “or $20”, which happens to be good enough for a hash on string identifiers.
To figure the trick, one needs to check the ASCII Table. (more…)
Recent commits to the DWScript repository doubled the compiler performance when compiling many small scripts, like happens in the unit tests suites.
This started from a first profiling run where the memory allocations around the UnicodeLowerCase function came out as top bottlenecks.
Thing is, Pascal being a case-insensitive language, there are lots of case-insensitive comparisons, lookups, searches and hashes, and turns out a key hash code was computed with code like
A tentative new language feature has been pushed to the DWScript repository: “property reintroduce”.
The aim is to allow a method to be reintroduced as a property, and do so in a non-fatal fashion so it can be pushed to production and existing code can be migrated iteratively. (more…)
For quite sometime the issue tracker at BitBucket has been barely usable, and Atlassian does not seem to have bothered fixing it… So if you have issues with DWScript, please now post them on the issues tracker of the GitHub DWScript mirror. (more…)