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Jeroen W. Pluimers on .NET, C#, Delphi, databases, and personal interests

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Archive for February 15th, 2017

Intel SSD back to life success story (using Lin… |Intel Communities

Posted by jpluimers on 2017/02/15

As many of other guys who have experienced that, I woke up one morning with “Operating system not found” and BAD_CTX as serial number. I was thousands miles from home and I only had the laptop itself and Ubuntu Live CD. I immediately started reading this forum and found the following: – the

[WayBack] Intel SSD back to life success story (using Lin… |Intel Communities


Posted in Uncategorized | 1 Comment »

HashLib4Pascal is a Delphi/FPC compatible library that provides an easy to use interface for computing hashes and checksums of strings (with a specified encoding), files, streams, byte arrays and untyped data to mention but a few.

Posted by jpluimers on 2017/02/15

One day I will need lots of hashing in Delphi: Xor-el/HashLib4Pascal: HashLib4Pascal is a Delphi/FPC compatible library that provides an easy to use interface for computing hashes and checksums of strings (with a specified encoding), files, streams, byte arrays and untyped data to mention but a few. [WayBack]

via: Hello all,I made a port of “HashLib” ( “with some fixes, additions and modifications” for Delphi (2010 ( I hope ) and above)… – Ugochukwu Mmaduekwe – Google+ [WayBack]

It’s a port of the C# HashLib – Home [WayBack]

Another fork is at


Posted in .NET, C#, Delphi, Delphi 10 Seattle, Delphi 10.1 Berlin (BigBen), Delphi 2010, Delphi XE, Delphi XE2, Delphi XE3, Delphi XE4, Delphi XE5, Delphi XE6, Delphi XE7, Delphi XE8, Development, Encoding, FreePascal, Pascal, Software Development | Leave a Comment »

Firebird – adjusting Delphi stored TDateTime (or OLE Automation date) fields that contain Dates, Times or DateTimes

Posted by jpluimers on 2017/02/15

Delphi programmers often store TDateTime (be it date, time or date+time values) as floating points in the database. They take the easy way out basically because TDateTime is nothing but a typed alias for the Delphi Double type (which is equivalent to the IEEE 754 double-precision binary floating-point format: binary64 type) .

Actually, TDateTime is equivalent to the OLE Automation date (which is described in the remarks of  DateTime.ToOADate Method (System)) which has an epoch of  midnight at 1899-12-30 (to be compatible with Lotus-123 including its leap-year-bug, background on that is at Why are the Microsoft Office file formats so complicated? (And some workarounds) – Joel on Software).

Anyway: the definition is this:

An OLE Automation date is implemented as a floating-point number whose integral component is the number of days before or after midnight, 30 December 1899, and whose fractional component represents the time on that day divided by 24. For example, midnight, 31 December 1899 is represented by 1.0; 6 A.M., 1 January 1900 is represented by 2.25; midnight, 29 December 1899 is represented by -1.0; and 6 A.M., 29 December 1899 is represented by -1.25.

The base OLE Automation Date is midnight, 30 December 1899. The minimum OLE Automation date is midnight, 1 January 0100. The maximum OLE Automation Date is the same as DateTime.MaxValue, the last moment of 31 December 9999.

The sample values are remarkably the same as the ones for TDateTime:

Value Description
0 December 30, 1899; 12:00 A.M.
2.75 January 1, 1900; 6:00 P.M.
-1.25 December 29, 1899; 6:00 A.M.
35065 January 1, 1996; 12:00 A.M.

The below SQL example uses the Firebird date/time/timestamp casting shortcuts:

select date      '1899-12-30'              + 42452.670590278 as Date20160323,
       timestamp '1899-12-30 00:00:00.000' + 42452.670590278 as DateTime20160323160539,
       time       '00:00:00'                + 60*60*24 * 0.5 as Noon,
       timestamp '1899-12-30 00:00:00.000' + 0          as DateTime18991230Midnight,
       timestamp '1899-12-30 00:00:00.000' + 2.75           as DateTime190001011800,
       timestamp '1899-12-30 00:00:00.000' + -1.25          as DateTime189912290600,
       timestamp '1899-12-30 00:00:00.000' + 35065          as DateTime19960101Midnight
from   rdb$database

Which – using DMY date format and 24 hour clock format settings – results in:

DATE20160323 DATETIME20160323160539 NOON       DATETIME18991230MIDNIGHT DATETIME190001011800 DATETIME189912290600 DATETIME19960101MIDNIGHT CONSTANT
24-3-2016    23-3-2016 16:05:39     12:00:00   30-12-1899               1-1-1900 18:00:00    28-12-1899 18:00:00  1-1-1996

Which basically taught me a new thing about firebird: Times are calculated in seconds, so date fractions need to be multiplied by 60 * 60 * 24.

You can see this in the following query and results:

select (cast('Now' as time) - cast('00:00:00.000' as time)) / (24 * 60 * 60) as DelphiTime,
        cast('Now' as time) - cast('00:00:00.000' as time) as SecondsSinceMidnight,
        cast('Now' as date) - cast('1899-12-30' as date) as DelphiDate,
        cast('Now' as timestamp) - cast('1899-12-30 00:00:00.000' as timestamp) as DelphiDateTime,
        24 * 60 * 60 as SecondsPerDay,
        cast('Now' as date) as "Date",
        cast('Now' as time) as "Time",
        cast('Now' as timestamp) as "TimeStamp"
from rdb$database
0,4366               37722,284            42835       42835,436600509      86400                10-4-2017  10:28:42     10-4-2017 10:28:42      

Note this post is complementary to Date format converter from Text or Unix/Mac/Filetime/Microsoft to virtually any readable form (which mentions the wrong Microsoft epoch as it should be 1899-12-30 midnight): the above shows how to do the conversion to readable dates in Firebird (might work in InterBase as well, but I’ve not used that for a long time).


PS: for Microsoft SQL Server: passing dates to the sql server: pass it as float – 2. -2 is the difference between delphi tdatetime start date and mssql start date.


Posted in Algorithms, Database Development, Development, Firebird, Floating point handling, Software Development | 2 Comments »

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