iam getting from c.dot net web service
byte[] data = new byte[] {-33, -96,0, 0, 0,0,0,0};
I want to convert this into long value
I tried this
long result = (long)ByteBuffer.wrap(index).getInt();
I am getting the result as -543162368 wheras actual value is 41183
First off you want to call getLong() instead of getInt() on the buffer.
However, the data you're receiving is little-endian, which means that it starts with the low order byte first. ByteBuffers are constructed as default with big endian order. You need to set the order to LITTLE_ENDIAN to get the correct value out.
ByteBuffer buffer = ByteBuffer.wrap(index)
buffer.order(ByteOrder.LITTLE_ENDIAN);
long result = buffer.getLong();
Since you apparently can't set the byte order or use getLong, you will need to do it like this:
// Reverse array
for (int i = 0; i < 4; ++i)
{
byte temp = data[i];
data[i] = data[8-i];
data[8-i] = temp;
}
// Get two ints and shift the first int into the high order bytes
// of the result.
ByteBuffer buffer = ByteBuffer.wrap(data);
long result = ((long)buffer.getInt()) << 32;
result |= (long)buffer.getInt();
result should now contain the value.
Related
I'm trying to write a function within a compute shader (HLSL) that accept an argument being an array on different size. The compiler always reject it.
Example (not working!):
void TestFunc(in uint SA[])
{
int K;
for (K = 0; SA[K] != 0; K++) {
// Some code using SA array
}
}
[numthreads(1, 1, 1)]
void CSMain(
uint S1[] = {1, 2, 3, 4 }; // Compiler happy and discover the array size
uint S2[] = {10, 20}; // Compiler happy and discover the array size
TestFunc(S1);
TestFunc(S2);
}
If I give an array size in TestFunc(), then the compiler is happy when calling TestFunc() passing that specific array size but refuse the call for another size.
You cannot have function parameters of indeterminate size.
You need to initialize an array of know length, and an int variable that holds the array length.
void TestFunc(in uint SA[4], in uint saCount)
{ int K;
for (K = 0; SA[K] != 0; K++)
{
// Some code using SA array, saCount is your array length;
}
}
[numthreads(1, 1, 1)]
void CSMain()
{
uint S1count = 4;
uint S1[] = {1, 2, 3, 4 };
uint S2count = 2;
uint S2[] = {10, 20,0,0};
TestFunc(S1, S1count);
TestFunc(S2, S2count);
}
In my example I have set your array max size as 4, but you can set it bigger if needed. You can also set multiple functions for different array lengths, of set up multiple passes if your data overflows your array max size.
Edit to answer comment
The issue is that array dimensions of function parameters must be explicit as the compiler error states. This cannot be avoided. What you can do however, is avoid passing the array at all. If you in-line your TestFunc in your CSMain, you avoid passing the array and your routine compiles and runs. I know it can make your code longer and harder to maintain, but it's the only way to do what you want with an array of unspecified length. The advantage is that this way you have access to array.Length that might make your code simpler.
I need to find a way to convert an arbitrary character typed by a user into an ASCII representation to be sent to a network service. My current approach is to create a lookup dictionary and send the corresponding code. After creating this dictionary, I see that it is hard to maintain and determine if it is complete:
__asciiKeycodes[#"F1"] = #(112);
__asciiKeycodes[#"F2"] = #(113);
__asciiKeycodes[#"F3"] = #(114);
//...
__asciiKeycodes[#"a"] = #(97);
__asciiKeycodes[#"b"] = #(98);
__asciiKeycodes[#"c"] = #(99);
Is there a better way to get ASCII character code from an arbitrary key typed by a user (using standard 104 keyboard)?
Objective C has base C primitive data types. There is a little trick you can do. You want to set the keyStroke to a char, and then cast it as an int. The default conversion in c from a char to an int is that char's ascii value. Here's a quick example.
char character= 'a';
NSLog("a = %ld", (int)test);
console output = a = 97
To go the other way around, cast an int as a char;
int asciiValue= (int)97;
NSLog("97 = %c", (char)asciiValue);
console output = 97 = a
Alternatively, you can do a direct conversion within initialization of your int or char and store it in a variable.
char asciiToCharOf97 = (char)97; //Stores 'a' in asciiToCharOf97
int charToAsciiOfA = (int)'a'; //Stores 97 in charToAsciiOfA
This seems to work for most keyboard keys, not sure about function keys and return key.
NSString* input = #"abcdefghijklkmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890!##$%^&*()_+[]\{}|;':\"\\,./<>?~ ";
for(int i = 0; i<input.length; i ++)
{
NSLog(#"Found (at %i): %i",i , [input characterAtIndex:i]);
}
Use stringWithFormat call and pass the int values.
I have a fairly complex issue regarding the interpretation of packets in an app that I am making. A host app sends a packet to client apps with the following structure:
[Header of 10 bytes][peerID of selected client of variable byte length][empty byte][peerID of a client of variable byte length][empty byte][int of 4 bytes][peerID of client of variable byte length][empty byte][int of 4 bytes]
Here is a sample packet that is produced under this structure:
434e4c50 00000000 006a3134 31303837 34393634 00313233 38313638 35383900 000003e8 31343130 38373439 36340000 0003e8
Converted it looks like this:
CNLP j1410874964 1238168589 Ë1410874964 Ë
"CNLP j" is the packet header of 10 bytes. "1410874964" is the peerID of the selected client. "1238168589" is the peerID of another client. " Ë" has an int value of 1000. "1410874964" is the peerID of the other client (in this case, the selected client). " Ë" also has an int value of 1000. Basically, in this packet I am communicating 2 things - who the selected client is and the int value associated with each client.
My problem exists on the interpretation side (client side). To interpret this particular type of packet, I use the following method:
+ (NSMutableDictionary *)infoFromData:(NSData *)data atOffset:(size_t) offset
{
size_t count;
NSMutableDictionary *info = [NSMutableDictionary dictionaryWithCapacity:8];
while (offset < [data length])
{
NSString *peerID = [data cnl_stringAtOffset:offset bytesRead:&count];
offset += count;
NSNumber *number = [NSNumber numberWithInteger:[data cnl_int32AtOffset:offset]];
offset += 4;
[info setObject:number forKey:peerID];
}
return info;
}
Typically, each of these packets range between 49 and 51 bytes. "offset" is set in a previous method to reflect the byte number after the packet header plus the empty byte after the selected player (in the case of the above packet, 21). "count" is initialized with a value of 1. In the case of this particular example, length is 51. The following method is passed the above arguments:
- (NSString *)cnl_stringAtOffset:(size_t)offset bytesRead:(size_t *)amount
{
const char *charBytes = (const char *)[self bytes];
NSString *string = [NSString stringWithUTF8String:charBytes + offset];
*amount = strlen(charBytes + offset) + 1;
return string;
}
This method is supposed to read through a variable length string in the packet, set the offset to the byte immediately after the empty byte pad behind the peerID string, and return the string that was read. "amount" is then set to the number of bytes the method read through for the string (this is becomes the new value of count after returning to the first method). "offset" and "count" are then added together to become the new "offset" - where interpretation of the int portion of the packet will begin. The above arguments are passed to the following method:
- (int)cnl_int32AtOffset:(size_t)offset
{
const int *intBytes = (const int *)[self bytes];
return ntohl(intBytes[offset / 4]);
}
This method is intended to return the 32 bit (4 byte) int value read at the current offset value of the packet. I believe that the problem exists in this method when the offset is a number that is not divisible by 4. In this case, the first int value of 1000 was correctly interpreted, and 32 was returned as the offset during the first iteration of the while loop. However, during the second iteration, the int value interpreted was 909377536 (obtained from reading bytes 36340000 in the packet instead of bytes 000003E8) This was likely due to the fact that the offset during this iteration was set to 47 (not divisible by 4). After interpreting the 32 bit int in the category above, 4 is added to the offset in the first method to account for a 4 byte (32 bit int). If my intuition about an offset not divisible by zero is correct, any suggestions to get around this problem are greatly appreciated. I have been looking for a way to solve this problem for quite some time and perhaps fresh eyes may help. Thanks for any help!!!
The unportable version (undefined behaviour for many reasons):
return ntohl(*(const int *)([self bytes]+offset));
A semi-portable version is somewhat trickier, but in C99 it appears that you can assume int32_t is "the usual" two's complement representation (no trap representations, no padding bits), thus:
// The cast is necessary to prevent arithmetic on void* which is nonstandard.
const uint8_t * p = (const uint8_t *)[self bytes]+offset;
// The casts ensure the result type is big enough to hold the shifted value.
// We use uint32_t to prevent UB when shifting into the sign bit.
uint32_t n = ((uint32_t)p[0]<<24) | ((uint32_t)p[1]<<16) | ((uint32_t)p[2]<<8) | ((uint32_t)p[3]);
// Jump through some hoops to prevent UB on "negative" numbers.
// An equivalent to the third expression is -(int32_t)~n-1.
// A good compiler should be able to optimize this into nothing.
return (n <= INT32_MAX) ? (int32_t)n : -(int32_t)(UINT32_MAX-n)-1;
This won't work on architectures without 8-bit bytes, but such architectures probably have different conventions for how things are passed over the network.
A good compiler should be able to optimize this into a single (possibly byte-swapped) load on suitable architectures.
I'm trying to implement an ARM/DSP shared memory communication. The ARM side puts a block of data on the shared memory (let'sa name it array[]) and sends the address and the size of the block to the DSP side which just reads them.
On the DSP side,
void * buf //address of block on shared memory
int length //size of block
However when I try to read them what i get is actually:
buf[0] = length
buf[1] = array[1]
buf[2] = array[2]
buf[3] = array[3]
:
:
:
It looks as if the length variable overights the first cell of the array (which is kind of strange) or I am using the void pointer the wrong way.
Any suggestions?
i think, that data structure is:
buf[0] = length
buf[1] = array[0]
buf[2] = array[1]
:
buf[length] = array[lenght-1]
and you must reserve buf for lenght+1
I have a binary file I've loaded using an NSData object. Is there a way to locate a sequence of characters, 'abcd' for example, within that binary data and return the offset without converting the entire file to a string? Seems like it should be a simple answer, but I'm not sure how to do it. Any ideas?
I'm doing this on iOS 3 so I don't have -rangeOfData:options:range: available.
I'm going to award this one to Sixteen Otto for suggesting strstr. I went and found the source code for the C function strstr and rewrote it to work on a fixed length Byte array--which incidentally is different from a char array as it is not null terminated. Here is the code I ended up with:
- (Byte*)offsetOfBytes:(Byte*)bytes inBuffer:(const Byte*)buffer ofLength:(int)len;
{
Byte *cp = bytes;
Byte *s1, *s2;
if ( !*buffer )
return bytes;
int i = 0;
for (i=0; i < len; ++i)
{
s1 = cp;
s2 = (Byte*)buffer;
while ( *s1 && *s2 && !(*s1-*s2) )
s1++, s2++;
if (!*s2)
return cp;
cp++;
}
return NULL;
}
This returns a pointer to the first occurrence of bytes, the thing I'm looking for, in buffer, the byte array that should contain bytes.
I call it like this:
// data is the NSData object
const Byte *bytes = [data bytes];
Byte* index = [self offsetOfBytes:tag inBuffer:bytes ofLength:[data length]];
Convert your substring to an NSData object, and search for those bytes in the larger NSData using rangeOfData:options:range:. Make sure that the string encodings match!
On iPhone, where that isn't available, you may have to do this yourself. The C function strstr() will give you a pointer to the first occurrence of a pattern within the buffer (as long as neither contain nulls!), but not the index. Here's a function that should do the job (but no promises, since I haven't tried actually running it...):
- (NSUInteger)indexOfData:(NSData*)needle inData:(NSData*)haystack
{
const void* needleBytes = [needle bytes];
const void* haystackBytes = [haystack bytes];
// walk the length of the buffer, looking for a byte that matches the start
// of the pattern; we can skip (|needle|-1) bytes at the end, since we can't
// have a match that's shorter than needle itself
for (NSUInteger i=0; i < [haystack length]-[needle length]+1; i++)
{
// walk needle's bytes while they still match the bytes of haystack
// starting at i; if we walk off the end of needle, we found a match
NSUInteger j=0;
while (j < [needle length] && needleBytes[j] == haystackBytes[i+j])
{
j++;
}
if (j == [needle length])
{
return i;
}
}
return NSNotFound;
}
This runs in something like O(nm), where n is the buffer length, and m is the size of the substring. It's written to work with NSData for two reasons: 1) that's what you seem to have in hand, and 2) those objects already encapsulate both the actual bytes, and the length of the buffer.
If you're using Snow Leopard, a convenient way is the new -rangeOfData:options:range: method in NSData that returns the range of the first occurrence of a piece of data. Otherwise, you can access the NSData's contents yourself using its -bytes method to perform your own search.
I had the same problem.
I solved it doing the other way round, compared to the suggestions.
first, I reformat the data (assume your NSData is stored in var rawFile) with:
NSString *ascii = [[NSString alloc] initWithData:rawFile encoding:NSAsciiStringEncoding];
Now, you can easily do string searches like 'abcd' or whatever you want using the NSScanner class and passing the ascii string to the scanner. Maybe this is not really efficient, but it works until the -rangeOfData method will be available for iPhone also.