OData does not include any bit-manipulation operators.
Is there a way to create a $filter equivalent to
column & mask = mask
column & mask = 0
with the available odata operators?
add, sub, div, mul, mod, neg, round, floor, ceiling
In my case mask can only contain a single bit
One idea I got is to declare a generic "flags" enum (e.g. Bits.Bit1, Bits.Bit2) and then use cast + has but don't know if it works.
It is not possible to test integers for bits on/off via the OData v4 interface.
A flags enum work fine but integers can't be casted to an enum. I.e. you must expose the column as an enum in the metadata.
In case if you need only checking that entity Enum properties contains any of [Flags] values, you can use 'has' operator.
http://docs.oasis-open.org/odata/odata/v4.0/cs02/part2-url-conventions/odata-v4.0-cs02-part2-url-conventions.html#_Toc372793313
Related
I still have not found a easy way to do a "filtering" Flow in AkkaStreams. Doing a "mapping" flow is clear to me, with fromFunction, but doing a filtering one is not. In RxJava/Reactor there is a compose operator on Flowable/Observable that takes a function from a Flowable to another Flowable, so then a transformation can be described as a chain of operators, and of course the filter operator on a Source is what I need for a filtering Flow, but it is unclear to me how to define a filtering Flow, though clearly it is easy for me how to filter a Source of course.
Please advise
// Filter elements which are even (use the modulo operator: `%`)
def filterEvenValues: Flow[Int, Int, NotUsed] =
Flow[Int].filter(number => number % 2 == 0)
I want to store IP Address using c++ in sqlite3 DB in hex format. I am using TEXT as the format for storing hex values. I want to perform a check on the value being inserted in the DB. The value range I want to check for is 0x00000000 - 0xFFFFFFFF. For INTEGER type you can check by - CHECK (num BETWEEN 0 AND 100). Is there any way to add check constraint for Hex Values?
If there is an smarter way to store IP address in SQLITE please share with me.
Thanks
I think you have two main choices: (a) store as hex (i.e. text) and check "hex conformity", or (b) store as integer and print it as hex when reading data.
There may be several reasons for preferring the one over the other, e.g. if the application actually provides and receives integer values. Anyway, some examples for option (a) and option (b).
Option (a) - store as text and check hex conformity
the probably simplest way is to use a check based on GLOB as remarked by CL:
value TEXT CONSTRAINT "valueIsHex" CHECK(value GLOB "0x[a-fA-F0-9][a-fA-F0-9][a-fA-F0-9][a-fA-F0-9][a-fA-F0-9][a-fA-F0-9][a-fA-F0-9][a-fA-F0-9]")
If logic goes beyond that supported by GLOB, you could install a user defined function, either a general regexp() function or a custom function for your specific needs. This could be the case, if you want to store a complete IP-address in one field and still want to do a conformity check. For help on general regexp() function, confer this SO answer. For help on user defined functions confer, for example, this StackOverflow answer.
Option (b) - store as int and print as hex
If your application is actually working with integers, then change your db schema to integer and add a check like:
value INTEGER CONSTRAINT "valueIsValid" CHECK(value <= 0xFFFFFFFF)
For convenience, you can still print the value as hex using a query (or defining a corresponding view) like the following:
select printf('%08X', value) from theTable
I'm implementing AES encryption. During the mix column/inverse mix columns procedures, I need to do Galois field multiplication. I'm using the look-up tables in the following document(Section 5.4.2)
https://www.ime.usp.br/~rt/cranalysis/AESSimplified.pdf
If you go to the section specified above, the (0,0) column in the L table is empty. So what do I return when say I need to look up L(0,0). I tried to return 0, but that's giving me the wrong encryption.
The original action is multiplication. Therefore, if your value is 0x00 you don't have to look it up in the L table, and the result of the whole multiplication is zero.
I have a mapping Nx2 between two set of encodings (not relevant: Unicode and GB18030) under this format:
Warning: huge XML, don't open if having slow connection:
http://source.icu-project.org/repos/icu/data/trunk/charset/data/xml/gb-18030-2000.xml
Snapshot:
<a u="00B7" b="A1 A4"/>
<a u="00B8" b="81 30 86 30"/>
<a u="00B9" b="81 30 86 31"/>
<a u="00BA" b="81 30 86 32"/>
I would like to save the b-values (right column) in a data structure and to access them directly (no searching) with indexes based on a-values (left column).
Example:
I can store those elements in a data structure like this:
unsigned short *my_page[256] = {my_00,my_01, ....., my_ff}
, where the elements are defined like:
static unsigned short my_00[256] etc.
.
So basically a matrix of matrix => 256x256 = 65536 available elements.
In the case of other encodings with less elements and different values (ex. Chinese Big5, Japanese Shift, Korean KSC etc), I can access the elements using a bijective function like this:
element = my_page[(unicode[i]>>8)&0x00FF][unicode[i]&0x00FF];, where unicode[i] is filled with the a-like elements from the mapping (as mentioned above). How do I generate and fill the my_page structure is analogous. For the working encodings, I have like around 7000 characters to store (and they are stored in a unique place in my_page).
The problem comes with the GB18030 encoding, trying to store 30861 elements in my_page (65536 elements). I am trying to use the same bijective function for filling (and then accessing, analogously) the my_page structure, but it fails since the access mode does not return unique results.
For example: For the unicode values, there are more than 1 element accessed via
my_page[(unicode[i]>>8)&0x00FF][unicode[i]&0x00FF] since the indexes can be the same for i and for i+1 for example. Do you know another way of accessing/filling the elements in the my_page structure based only on pre-computed indexes like I was trying to do?
I assume I have to use something like a pseudo-hash function that returns me a range of values VRange and based on a set of rules I can extract from the range VRange the integer indexes of my_page[256][256].
If you have any advice, please let me know :)
Thank you !
For GB18030, refer to this document: http://icu-project.org/docs/papers/gb18030.html
As explained in this article:
“The number of valid byte sequences -- of Unicode code points covered and of mappings defined between them -- makes it impractical to directly use a normal, purely mapping-table-based codepage converter. With about 1.1 million mappings, a simple mapping table would be several megabytes in size.”
So most probably is not good to implement a conversion based on a pure mapping table.
For large parts, there is a direct mapping between GB18030 and Unicode. Most of the four-bytes characters can be translated algorithmically. The author of the article suggests to handle them such ranges with a special code, and the other ones with a classic mapping table. These characters are the ones given in the XML mapping table: http://source.icu-project.org/repos/icu/data/trunk/charset/data/xml/gb-18030-2000.xml
Therefore, the index-based access on Matrix-like structure in C++ can be a problem opened for whom wants to research on such bijective functions.
My users will in some cases be able to view a web version of a database table that stores data they've entered. For various reasons I need to include all the stored data, including a number of integer flags for each record that encapsulate adjacencies and so forth within the data (this is for speed and convenience at runtime). But rather than exposing them one-for-one in the webview, I'd like to have an obfuscated field that's just called "reserved" and contains a single unintelligible string representing those flags that I can easily encode and decode.
How can I do this efficiently in C++/Objective C?
Thanks!
Is it necessary that this field is exposed to the user visually, or just that it’s losslessly captured in the HTML content of the webview? If possible, can you include the flags as a hidden input element with each row, i.e., <input type=“hidden” …?
Why not convert each of the fields to hex, and append them as a string and save that value?
As long as you always append the strings in the same order, breaking them back apart and converting them back to numbers should be trivial.
Use symmetric encryption (example) to encode and decode the values. Of course, only you should know of the key.
Alternatively, Assymetric RSA is more powerfull encryption but is less efficient and is more complex to use.
Note: i am curios about the "various reasons" that require this design...
Multiply your flag integer by 7, add 3, and convert to base-36. To check if the resulting string is modified, convert back to base-2, and check if the result modulo 7 is still 3. If so, divide by 7 to get the flags. note that this is subject to replay attacks - users can copy any valid string in.
Just calculate a CRC-32 (or similar) and append it to your value. That will tell you, with a very high probability, if your value has been corrupted.