I am just trying to implement 32-bit CRC Algorithm with initial seed of 0x0 to check a xml string integrity in .net wcf application.
i am returning a Xml string.and the fixed-length
hexadecimal string generated from the value of the CRC . how can i implement CRC alogirthm for a xml string and convert CRC to hexadecimal string.
zlib provides a crc32() function for this purpose. A little bit of googling will turn up many other implementations in source code.
Related
sjcl.js provides codecs for reading in hex strings and utf8Strings, but it doesn't provide a codec for reading in base-10 integer strings. I'm trying to read in private keys for ECC point generation that are from another program (going from codec to bitArray then from bitArray to bn). Seems like an odd oversight which leads me to believe it is in there somewhere, just missing it.
Thanks,
PeterT
I'm currently using Erlang for a big project but i have a question regarding a proper proceeding.
I receive bytes over a tcp socket. The bytes are according to a fixed protocol, the sender is a pyton client. The python client uses class inheritance to create bytes from the objects.
Now i would like to (in Erlang) take the bytes and convert these to their equivelant messages, they all have a common message header.
How can i do this as generic as possible in Erlang?
Kind Regards,
Me
Pattern matching/binary header consumption using Erlang's binary syntax. But you will need to know either exactly what bytes or bits your are expecting to receive, or the field sizes in bytes or bits.
For example, let's say that you are expecting a string of bytes that will either begin with the equivalent of the ASCII strings "PUSH" or "PULL", followed by some other data you will place somewhere. You can create a function head that matches those, and captures the rest to pass on to a function that does "push()" or "pull()" based on the byte header:
operation_type(<<"PUSH", Rest/binary>>) -> push(Rest);
operation_type(<<"PULL", Rest/binary>>) -> pull(Rest).
The bytes after the first four will now be in Rest, leaving you free to interpret whatever subsequent headers or data remain in turn. You could also match on the whole binary:
operation_type(Bin = <<"PUSH", _/binary>>) -> push(Bin);
operation_type(Bin = <<"PULL", _/binary>>) -> pull(Bin).
In this case the "_" variable works like it always does -- you're just checking for the lead, essentially peeking the buffer and passing the whole thing on based on the initial contents.
You could also skip around in it. Say you knew you were going to receive a binary with 4 bytes of fluff at the front, 6 bytes of type data, and then the rest you want to pass on:
filter_thingy(<<_:4/binary, Type:6/binary, Rest/binary>>) ->
% Do stuff with Rest based on Type...
It becomes very natural to split binaries in function headers (whether the data equates to character strings or not), letting the "Rest" fall through to appropriate functions as you go along. If you are receiving Python pickle data or something similar, you would want to write the parsing routine in a recursive way, so that the conclusion of each data type returns you to the top to determine the next type, with an accumulated tree that represents the data read so far.
I only covered 8-bit bytes above, but there is also a pure bitstring syntax, which lets you go as far into the weeds with bits and bytes as you need with the same ease of syntax. Matching is a real lifesaver here.
Hopefully this informed more than confused. Binary syntax in Erlang makes this the most pleasant binary parsing environment in a general programming language I've yet encountered.
http://www.erlang.org/doc/programming_examples/bit_syntax.html
I need to convert a ByteString to a Float32 (Exactly a 32-bit big-endian IEEE 754 floating point number). The ByteString is a part of an open sound control stream, received via UDP client.
I've spent a lot of time researching, so I'd like of someone handy with Smalltalk could give me a solution.
Thanks, in advance.
Since you seem to be receiving binary data, and not a decimal number in formatted ASCII, I would not recommend to call it ByteString, but rather ByteArray, Strings are an abstraction for containing characters, not bits.
In the case of VisualWorks, there is a class called UninterpretedBytes specialized in storing raw data (bits or rather bytes) for later interpretation.
This class has all the message you need to interpret the bytes, like for example #floatAt:bigEndian:
| yourBinaryStream buffer |
yourBinaryStream := ... insert some code to create your stream here...
buffer:= UninterpretedBytes from: (yourBinaryStream next: 4).
nextFloat := buffer floatAt: 1 bigEndian: true
In Pharo Smalltalk you can do:
(Float readFrom: '4.2') asIEEE32BitWord
readFrom: just reads a float from a string, and then you convert it to IEEE 754...
In VisualWorks you need to use the superclass method readFrom: as implemented in class Number.
First create a readstream on the string, for example:
Number readFrom: '192843.887' readStream
I've been banging my head for the last couple of hours with what seemed to be a very easy task.
My app is communicating with a server over tcpip. The protocol requires that the first 4 bytes of each request be the length of the stream, in reverse order. For example, if the length if 13, I need to supply (decimal) {0,0,0,13}; if it's 300, I need to supply {0,0,44,256}. Then, the actual data follows.
Apparently this is something very straightforward to do in Java, and also in VB (e.g. BitConverter.GetBytes(sendString.Length).Reverse().ToArray()). But in obj-c I just couldn't make it work, I've tried all sorts of conversions between NSString/NSData/NSArray, with no luck.
Thanks in advance!
The server is asking for the data in big-endian order (most significant byte first). Big-endian is the standard network byte order for Internet protocols (including IP, TCP, UDP, DNS, and lots more). It happens that you're compiling for a little-endian platform, so you need to swap the bytes.
However, you should not rely on being on a little-endian platform. Instead, you should make your code independent of the local (host) byte order, using the Core Foundation byte-swapping functions.
Specifically, you should use CFSwapInt32HostToBig to convert your 4-byte int to big-endian order. On a little-endian platform, this rearranges the bytes. On a big-endian platform, this does nothing.
Similarly, you should use CFSwapInt32BigToHost to convert the 4-byte ints you receive from the server to your host byte order.
Alternatively, you can use the standard POSIX byte-swapping functions. The htonl function stands for host-to-network-long, and converts a 32-bit int from host order to network (big-endian) order. The ntohl function converts a 32-bit int from network to host order. (Back when these functions were created, some popular operating systems had 16-bit ints and 32-bit longs. Can you believe it?)
NSInteger a = 300; //13;
char* aa = &a;
Byte b[] = {0,0,0,0};
memcpy(&b[0], &aa[3], 1);
memcpy(&b[1], &aa[2], 1);
memcpy(&b[2], &aa[1], 1);
memcpy(&b[3], &aa[0], 1);
As indicated in the accepted answer for the duplicate question, Foundation provides functions for byte swapping. In this case, since you're dealing with a long, you probably want NSSwapLong.
I'm trying to implement WebSocket handshake (76) in ObjC and can't figure out (as I'm new to C and ObjC) how can I get the following:
List item
I've got two number
155712099
173347027
I need to convert them to 32 bit big-endian numbers
concatenate them into a string
and express the resulting string in ASCII
Help is highly appreciated.
Since you're using the iPhone SDK, you have access to Core Foundation. Use:
uint32_t myInt32Value = ...;
uint32_t myInt32AsABigEndianNumber = CFSwapInt32HostToBig(myInt32Value);
Objective-C is based on C and usually has the C standard library available, so you can use the standard htonl function. You can then do the string manipulation using the normal string functions.