Related
I'll get right to the question,
We have this block of C# code
using (Rfc2898DeriveBytes pbkdf2 = new Rfc2898DeriveBytes(password, passwordSaltBytes, iterationCount))
{
pbkdf2Bytes = pbkdf2.GetBytes(derivedLength + iterationCountBytes.Length);
}
Returns a byte array, first index has a value of 252
We attempt the same thing in PHP:
$key = hash_pbkdf2("SHA1", $password, $password.$salt, $iterationCount, 48);
First index is 102...
The values all match before this specific part.
It's just that hashing function that isn't giving me consistent results.
Any help is appreciated, cheers.
Edit - If it's not obvious, I'm trying to understand why those two values don't match, what encoding/decoding etc. am I misunderstanding or doing incorrectly.
This is the full C# code. As you can see there are some unnecessary loops etc. but the reasons why this wasn't working are 2:
As somebody pointed out, the bytes in PHP do no output raw data by default, and thus the hash (and consequently as such,) its bytes, weren't identical with that of the C# script.
Previously, I thought (as others also pointed out) that I should pass in the $salt as it is without any encoding or transformation. But upon looking closer at the actual C# code... we can see in the 2nd for i loop that they're actually appending saltBytes onto passwordBytes, thus creating something similar to $password.$salt in PHP
Combining the two above issues:
Sending the $password.$salt instead of just one, and then setting the $raw_output option to true, outputs the same hash, the same bytes as C# does.
byte[] passwordBytes = Encoding.UTF8.GetBytes(password);
byte[] saltBytes = Encoding.UTF8.GetBytes(salt);
byte[] iterationCountBytes = BitConverter.GetBytes(iterationCount);
int derivedLength = passwordBytes.Length + saltBytes.Length;
byte[] passwordSaltBytes = new byte[derivedLength];
byte[] pbkdf2Bytes;
string encryptedString;
for (int i = 0; i < passwordBytes.Length; i++)
{
passwordSaltBytes[i] = passwordBytes[i];
}
for (int i = 0; i < saltBytes.Length; i++)
{
passwordSaltBytes[passwordBytes.Length + i] = saltBytes[i];
}
using (Rfc2898DeriveBytes pbkdf2 = new Rfc2898DeriveBytes(password, passwordSaltBytes, iterationCount))
{
pbkdf2Bytes = pbkdf2.GetBytes(derivedLength + iterationCountBytes.Length);
}
Thanks.
I have a Base64 encoded string and I am using the following c# code to decode it. Inside should be a range of Signed integers stored in 16bit.
Now I need to do it in PHP but I'm having real trouble. Can anyone help?
Basically can anyone convert this code to php?
private string decode(string encoded)
{
Byte[] newBytes = Convert.FromBase64String(
encoded.Replace("\n","")
);
int[] newArr = new int[newBytes.Length / 4];
for (int ctr = 0; ctr < newBytes.Length / 4; ctr++)
newArr[ctr] = BitConverter.ToInt16(newBytes, ctr * 4);
return DisplayArray(newArr);
}
private string DisplayArray(Array arr)
{
string output = "";
for (int ctr = 0; ctr < arr.GetUpperBound(0); ctr++)
{
output += arr.GetValue(ctr) + ",";
}
return output;
}
Here is the base64 string....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and it should decode to...
2,0,0,2,2,2,2,2,2,5,5,5,2,0,0,7,5,5,0,0,0,2,5,5,2,2,0,0,0,2,0,2,5,2,2,2,2,5,2,2,5,5,0,5,2,2,0,5,5,0,2,0,2,2,5,7,5,2,0,2,2,2,2,5,5,2,0,2,2,5,0,-2,2,2,0,2,0,5,5,0,2,2,2,0,0,2,2,2,5,2,5,7,5,5,5,7,7,5,7,7,5,7,7,7,5,2,-2,2,2,5,5,2,2,2,7,2,5,5,0,7,2,5,0,2,2,7,5,2,2,2,7,7,7,7,5,2,5,5,5,10,10,7,10,10,10,12,12,12,17,15,20,20,20,22,17,20,20,22,25,27,27,27,32,35,40,40,40,40,40,37,37,37,40,42,37,35,30,35,25,25,20,15,10,7,2,7,5,2,2,0,0,-2,0,2,-2,0,5,2,0,5,0,0,0,-2,0,-2,0,-2,-2,-5,-2,0,-5,-2,-2, etc...
The good
PHP makes it really easy to read in base64 data and convert it to an array of signed integers. Make sure to read up on the unpack function, it's great.
$stringValue = base64_decode($base64data, true);
$integers = unpack("s*", $stringValue);
The bad
That is not what your C# code is doing. After converting the base64 into raw bytes, it then processes that data in chunks of 4 bytes, parsing the first 2 into an int16 and throwing away the second two bytes. Half your data goes down the drain.
The ugly
If the C# code is really the algorithm you are after, here is how to do it in PHP:
$stringValue = base64_decode($base64data, true);
$integers = unpack("s*", $stringValue);
// Throw away half of our data. Because... why not? :)
$integers = array_map('array_shift', array_chunk($integers, 2));
I have to calculate CRC32 checksum for a string in C# and send it to an external application.
On the other end they will calculate it using Java.
But my checksum does not match on the their end.
e.g. CRC32 checksum of the following string
43HLV109520DAP10072la19z6
is 1269993351 on their end.
And 2947932745 at my end using C#
Please tell me what's going wrong in my code.
I am using this 0xffffffff default seed and following crc table
readonly static uint[] CRCTable = new uint[] {
0x00000000, 0x77073096, 0xEE0E612C, 0x990951BA, 0x076DC419,
0x706AF48F, 0xE963A535, 0x9E6495A3, 0x0EDB8832, 0x79DCB8A4,
0xE0D5E91E, 0x97D2D988, 0x09B64C2B, 0x7EB17CBD, 0xE7B82D07,
0x90BF1D91, 0x1DB71064, 0x6AB020F2, 0xF3B97148, 0x84BE41DE,
0x1ADAD47D, 0x6DDDE4EB, 0xF4D4B551, 0x83D385C7, 0x136C9856,
0x646BA8C0, 0xFD62F97A, 0x8A65C9EC, 0x14015C4F, 0x63066CD9,
0xFA0F3D63, 0x8D080DF5, 0x3B6E20C8, 0x4C69105E, 0xD56041E4,
0xA2677172, 0x3C03E4D1, 0x4B04D447, 0xD20D85FD, 0xA50AB56B,
0x35B5A8FA, 0x42B2986C, 0xDBBBC9D6, 0xACBCF940, 0x32D86CE3,
0x45DF5C75, 0xDCD60DCF, 0xABD13D59, 0x26D930AC, 0x51DE003A,
0xC8D75180, 0xBFD06116, 0x21B4F4B5, 0x56B3C423, 0xCFBA9599,
0xB8BDA50F, 0x2802B89E, 0x5F058808, 0xC60CD9B2, 0xB10BE924,
0x2F6F7C87, 0x58684C11, 0xC1611DAB, 0xB6662D3D, 0x76DC4190,
0x01DB7106, 0x98D220BC, 0xEFD5102A, 0x71B18589, 0x06B6B51F,
0x9FBFE4A5, 0xE8B8D433, 0x7807C9A2, 0x0F00F934, 0x9609A88E,
0xE10E9818, 0x7F6A0DBB, 0x086D3D2D, 0x91646C97, 0xE6635C01,
0x6B6B51F4, 0x1C6C6162, 0x856530D8, 0xF262004E, 0x6C0695ED,
0x1B01A57B, 0x8208F4C1, 0xF50FC457, 0x65B0D9C6, 0x12B7E950,
0x8BBEB8EA, 0xFCB9887C, 0x62DD1DDF, 0x15DA2D49, 0x8CD37CF3,
0xFBD44C65, 0x4DB26158, 0x3AB551CE, 0xA3BC0074, 0xD4BB30E2,
0x4ADFA541, 0x3DD895D7, 0xA4D1C46D, 0xD3D6F4FB, 0x4369E96A,
0x346ED9FC, 0xAD678846, 0xDA60B8D0, 0x44042D73, 0x33031DE5,
0xAA0A4C5F, 0xDD0D7CC9, 0x5005713C, 0x270241AA, 0xBE0B1010,
0xC90C2086, 0x5768B525, 0x206F85B3, 0xB966D409, 0xCE61E49F,
0x5EDEF90E, 0x29D9C998, 0xB0D09822, 0xC7D7A8B4, 0x59B33D17,
0x2EB40D81, 0xB7BD5C3B, 0xC0BA6CAD, 0xEDB88320, 0x9ABFB3B6,
0x03B6E20C, 0x74B1D29A, 0xEAD54739, 0x9DD277AF, 0x04DB2615,
0x73DC1683, 0xE3630B12, 0x94643B84, 0x0D6D6A3E, 0x7A6A5AA8,
0xE40ECF0B, 0x9309FF9D, 0x0A00AE27, 0x7D079EB1, 0xF00F9344,
0x8708A3D2, 0x1E01F268, 0x6906C2FE, 0xF762575D, 0x806567CB,
0x196C3671, 0x6E6B06E7, 0xFED41B76, 0x89D32BE0, 0x10DA7A5A,
0x67DD4ACC, 0xF9B9DF6F, 0x8EBEEFF9, 0x17B7BE43, 0x60B08ED5,
0xD6D6A3E8, 0xA1D1937E, 0x38D8C2C4, 0x4FDFF252, 0xD1BB67F1,
0xA6BC5767, 0x3FB506DD, 0x48B2364B, 0xD80D2BDA, 0xAF0A1B4C,
0x36034AF6, 0x41047A60, 0xDF60EFC3, 0xA867DF55, 0x316E8EEF,
0x4669BE79, 0xCB61B38C, 0xBC66831A, 0x256FD2A0, 0x5268E236,
0xCC0C7795, 0xBB0B4703, 0x220216B9, 0x5505262F, 0xC5BA3BBE,
0xB2BD0B28, 0x2BB45A92, 0x5CB36A04, 0xC2D7FFA7, 0xB5D0CF31,
0x2CD99E8B, 0x5BDEAE1D, 0x9B64C2B0, 0xEC63F226, 0x756AA39C,
0x026D930A, 0x9C0906A9, 0xEB0E363F, 0x72076785, 0x05005713,
0x95BF4A82, 0xE2B87A14, 0x7BB12BAE, 0x0CB61B38, 0x92D28E9B,
0xE5D5BE0D, 0x7CDCEFB7, 0x0BDBDF21, 0x86D3D2D4, 0xF1D4E242,
0x68DDB3F8, 0x1FDA836E, 0x81BE16CD, 0xF6B9265B, 0x6FB077E1,
0x18B74777, 0x88085AE6, 0xFF0F6A70, 0x66063BCA, 0x11010B5C,
0x8F659EFF, 0xF862AE69, 0x616BFFD3, 0x166CCF45, 0xA00AE278,
0xD70DD2EE, 0x4E048354, 0x3903B3C2, 0xA7672661, 0xD06016F7,
0x4969474D, 0x3E6E77DB, 0xAED16A4A, 0xD9D65ADC, 0x40DF0B66,
0x37D83BF0, 0xA9BCAE53, 0xDEBB9EC5, 0x47B2CF7F, 0x30B5FFE9,
0xBDBDF21C, 0xCABAC28A, 0x53B39330, 0x24B4A3A6, 0xBAD03605,
0xCDD70693, 0x54DE5729, 0x23D967BF, 0xB3667A2E, 0xC4614AB8,
0x5D681B02, 0x2A6F2B94, 0xB40BBE37, 0xC30C8EA1, 0x5A05DF1B,
0x2D02EF8D
};
CRC32 is calculated over a sequence of bytes and not over a string. So to calculate CRC32 you need to transform the string into bytes first. If you use a different encoding to transform a string to a sequence of bytes the result will be different.
Thus you need to use the same encoding on both sides. I recommend using UTF-8 without BOM.
I have calculated CRC32 with Java and got the same you got in C#. I.e. CRC32(43HLV109520DAP10072la19z6)=2947932745. This means that either they have a bug in java, or you have a bug during transmission.
Code follows.
I suggest you try to send simple data to java application, like zeros or ones, and try to deduce how do they compute CRC.
public static void main(String[] args) {
CRC32 crc32 = new CRC32();
String data = "43HLV109520DAP10072la19z6";
String[] cs = new String[] {"utf8" /*, "cp1252", "cp866" */};
byte[] array;
byte b;
for(int i=0; i<cs.length; ++i) {
array = data.getBytes(Charset.forName(cs[i]));
crc32.reset();
crc32.update(array);
System.out.println(String.format("%s: %d", cs[i], crc32.getValue()));
/*
for(int j=0; j<array.length/2; j++) {
b = array[i];
array[i] = array[array.length-1-i];
array[array.length-1-i] = b;
}
*/
for(int j=0; j<array.length; j+=2) {
b = array[i];
array[i] = array[i+2];
array[i+1] = b;
}
crc32.reset();
crc32.update(array);
System.out.println(String.format("of modified: %d", crc32.getValue()));
}
}
UPDATE
Endiannes reverse also not help
for(int j=0; j<array.length; j+=4) {
b = array[i];
array[i] = array[i+3];
array[i+3] = b;
b = array[i+1];
array[i+1] = array[i+2];
array[i+2] = b;
}
Without delving into any detail, the problem can be related to Java's lack of unsigned integer types. The problem could happen at the int level, but also at the byte level. This is one avenue of investigation.
CRC is calculated over a sequence of bytes and not over a string.
Whichever CRC in java looks different due unavailability of Unsigned int in java.
Convert calculated Int CRC into Hex String and take last 2 Bytes (length 4)
That is your actual CRC unsigned Int.
String hexCrc = Integer.toHexString(crcCalculated);
hexCrc = hexCrc.substring(hexCrc.length()-4);
compare hex CRC of c# and Java both should be same.
This question already has answers here:
What is the equivalent of memset in C#?
(17 answers)
Closed 8 years ago.
I'm busy rewriting an old project that was done in C++, to C#.
My task is to rewrite the program so that it functions as close to the original as possible.
During a bunch of file-handling the previous developer who wrote this program creates a structure containing a ton of fields that correspond to the set format that a file has to be written in, so all that work is already done for me.
These fields are all byte arrays. What the C++ code then does is use memset to set this entire structure to all spaces characters (0x20). One line of code. Easy.
This is very important as the utility that this file eventually goes to is expecting the file in this format. What I've had to do is change this struct to a class in C#, but I cannot find a way to easily initialize each of these byte arrays to all space characters.
What I've ended up having to do is this in the class constructor:
//Initialize all of the variables to spaces.
int index = 0;
foreach (byte b in UserCode)
{
UserCode[index] = 0x20;
index++;
}
This works fine, but I'm sure there must be a simpler way to do this. When the array is set to UserCode = new byte[6] in the constructor the byte array gets automatically initialized to the default null values. Is there no way that I can make it become all spaces upon declaration, so that when I call my class' constructor that it is initialized straight away like this? Or some memset-like function?
For small arrays use array initialisation syntax:
var sevenItems = new byte[] { 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20 };
For larger arrays use a standard for loop. This is the most readable and efficient way to do it:
var sevenThousandItems = new byte[7000];
for (int i = 0; i < sevenThousandItems.Length; i++)
{
sevenThousandItems[i] = 0x20;
}
Of course, if you need to do this a lot then you could create a helper method to help keep your code concise:
byte[] sevenItems = CreateSpecialByteArray(7);
byte[] sevenThousandItems = CreateSpecialByteArray(7000);
// ...
public static byte[] CreateSpecialByteArray(int length)
{
var arr = new byte[length];
for (int i = 0; i < arr.Length; i++)
{
arr[i] = 0x20;
}
return arr;
}
Use this to create the array in the first place:
byte[] array = Enumerable.Repeat((byte)0x20, <number of elements>).ToArray();
Replace <number of elements> with the desired array size.
You can use Enumerable.Repeat()
Enumerable.Repeat generates a sequence that contains one repeated value.
Array of 100 items initialized to 0x20:
byte[] arr1 = Enumerable.Repeat((byte)0x20,100).ToArray();
var array = Encoding.ASCII.GetBytes(new string(' ', 100));
If you need to initialise a small array you can use:
byte[] smallArray = new byte[] { 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20 };
If you have a larger array, then you could use:
byte[] bitBiggerArray Enumerable.Repeat(0x20, 7000).ToArray();
Which is simple, and easy for the next guy/girl to read. And will be fast enough 99.9% of the time.
(Normally will be the BestOption™)
However if you really really need super speed, calling out to the optimized memset method, using P/invoke, is for you:
(Here wrapped up in a nice to use class)
public static class Superfast
{
[DllImport("msvcrt.dll",
EntryPoint = "memset",
CallingConvention = CallingConvention.Cdecl,
SetLastError = false)]
private static extern IntPtr MemSet(IntPtr dest, int c, int count);
//If you need super speed, calling out to M$ memset optimized method using P/invoke
public static byte[] InitByteArray(byte fillWith, int size)
{
byte[] arrayBytes = new byte[size];
GCHandle gch = GCHandle.Alloc(arrayBytes, GCHandleType.Pinned);
MemSet(gch.AddrOfPinnedObject(), fillWith, arrayBytes.Length);
gch.Free();
return arrayBytes;
}
}
Usage:
byte[] oneofManyBigArrays = Superfast.InitByteArray(0x20,700000);
Maybe these could be helpful?
What is the equivalent of memset in C#?
http://techmikael.blogspot.com/2009/12/filling-array-with-default-value.html
Guys before me gave you your answer. I just want to point out your misuse of foreach loop. See, since you have to increment index standard "for loop" would be not only more compact, but also more efficient ("foreach" does many things under the hood):
for (int index = 0; index < UserCode.Length; ++index)
{
UserCode[index] = 0x20;
}
This is a faster version of the code from the post marked as the answer.
All of the benchmarks that I have performed show that a simple for loop that only contains something like an array fill is typically twice as fast if it is decrementing versus if it is incrementing.
Also, the array Length property is already passed as the parameter so it doesn't need to be retrieved from the array properties. It should also be pre-calculated and assigned to a local variable.
Loop bounds calculations that involve a property accessor will re-compute the value of the bounds before each iteration of the loop.
public static byte[] CreateSpecialByteArray(int length)
{
byte[] array = new byte[length];
int len = length - 1;
for (int i = len; i >= 0; i--)
{
array[i] = 0x20;
}
return array;
}
Just to expand on my answer a neater way of doing this multiple times would probably be:
PopulateByteArray(UserCode, 0x20);
which calls:
public static void PopulateByteArray(byte[] byteArray, byte value)
{
for (int i = 0; i < byteArray.Length; i++)
{
byteArray[i] = value;
}
}
This has the advantage of a nice efficient for loop (mention to gwiazdorrr's answer) as well as a nice neat looking call if it is being used a lot. And a lot mroe at a glance readable than the enumeration one I personally think. :)
The fastest way to do this is to use the api:
bR = 0xFF;
RtlFillMemory(pBuffer, nFileLen, bR);
using a pointer to a buffer, the length to write, and the encoded byte. I think the fastest way to do it in managed code (much slower), is to create a small block of initialized bytes, then use Buffer.Blockcopy to write them to the byte array in a loop. I threw this together but haven't tested it, but you get the idea:
long size = GetFileSize(FileName);
// zero byte
const int blocksize = 1024;
// 1's array
byte[] ntemp = new byte[blocksize];
byte[] nbyte = new byte[size];
// init 1's array
for (int i = 0; i < blocksize; i++)
ntemp[i] = 0xff;
// get dimensions
int blocks = (int)(size / blocksize);
int remainder = (int)(size - (blocks * blocksize));
int count = 0;
// copy to the buffer
do
{
Buffer.BlockCopy(ntemp, 0, nbyte, blocksize * count, blocksize);
count++;
} while (count < blocks);
// copy remaining bytes
Buffer.BlockCopy(ntemp, 0, nbyte, blocksize * count, remainder);
This function is way faster than a for loop for filling an array.
The Array.Copy command is a very fast memory copy function. This function takes advantage of that by repeatedly calling the Array.Copy command and doubling the size of what we copy until the array is full.
I discuss this on my blog at https://grax32.com/2013/06/fast-array-fill-function-revisited.html (Link updated 12/16/2019). Also see Nuget package that provides this extension method. http://sites.grax32.com/ArrayExtensions/
Note that this would be easy to make into an extension method by just adding the word "this" to the method declarations i.e. public static void ArrayFill<T>(this T[] arrayToFill ...
public static void ArrayFill<T>(T[] arrayToFill, T fillValue)
{
// if called with a single value, wrap the value in an array and call the main function
ArrayFill(arrayToFill, new T[] { fillValue });
}
public static void ArrayFill<T>(T[] arrayToFill, T[] fillValue)
{
if (fillValue.Length >= arrayToFill.Length)
{
throw new ArgumentException("fillValue array length must be smaller than length of arrayToFill");
}
// set the initial array value
Array.Copy(fillValue, arrayToFill, fillValue.Length);
int arrayToFillHalfLength = arrayToFill.Length / 2;
for (int i = fillValue.Length; i < arrayToFill.Length; i *= 2)
{
int copyLength = i;
if (i > arrayToFillHalfLength)
{
copyLength = arrayToFill.Length - i;
}
Array.Copy(arrayToFill, 0, arrayToFill, i, copyLength);
}
}
You can use a collection initializer:
UserCode = new byte[]{0x20,0x20,0x20,0x20,0x20,0x20};
This will work better than Repeat if the values are not identical.
You could speed up the initialization and simplify the code by using the the Parallel class (.NET 4 and newer):
public static void PopulateByteArray(byte[] byteArray, byte value)
{
Parallel.For(0, byteArray.Length, i => byteArray[i] = value);
}
Of course you can create the array at the same time:
public static byte[] CreateSpecialByteArray(int length, byte value)
{
var byteArray = new byte[length];
Parallel.For(0, length, i => byteArray[i] = value);
return byteArray;
}
I have a very painful library which, at the moment, is accepting a C# string as a way to get arrays of data; apparently, this makes marshalling for pinvokes easier.
So how do I make a ushort array into a string by bytes? I've tried:
int i;
String theOutData = "";
ushort[] theImageData = inImageData.DataArray;
//this is as slow like molasses in January
for (i = 0; i < theImageData.Length; i++) {
byte[] theBytes = System.BitConverter.GetBytes(theImageData[i]);
theOutData += String.Format("{0:d}{1:d}", theBytes[0], theBytes[1]);
}
I can do it this way, but it doesn't finish in anything remotely close to a sane amount of time.
What should I do here? Go unsafe? Go through some kind of IntPtr intermediate?
If it were a char* in C++, this would be significantly easier...
edit: the function call is
DataElement.SetByteValue(string inArray, VL Length);
where VL is a 'Value Length', a DICOM type, and the function itself is generated as a wrapper to a C++ library by SWIG. It seems that the representation chosen is string, because that can cross managed/unmanaged boundaries relatively easily, but throughout the C++ code in the project (this is GDCM), the char* is simply used as a byte buffer. So, when you want to set your image buffer pointer, in C++ it's fairly simple, but in C#, I'm stuck with this weird problem.
This is hackeration, and I know that probably the best thing is to make the SWIG library work right. I really don't know how to do that, and would rather a quick workaround on the C# side, if such exists.
P/Invoke can actually handle what you're after most of the time using StringBuilder to create writable buffers, for example see pinvoke.net on GetWindowText and related functions.
However, that aside, with data as ushort, I assume that it is encoded in UTF-16LE. If that is the case you can use Encoding.Unicode.GetString(), but that will exepect a byte array rather than a ushort array. To turn your ushorts into bytes, you can allocate a separate byte array and use Buffer.BlockCopy, something like this:
ushort[] data = new ushort[10];
for (int i = 0; i < data.Length; ++i)
data[i] = (char) ('A' + i);
string asString;
byte[] asBytes = new byte[data.Length * sizeof(ushort)];
Buffer.BlockCopy(data, 0, asBytes, 0, asBytes.Length);
asString = Encoding.Unicode.GetString(asBytes);
However, if unsafe code is OK, you have another option. Get the start of the array as a ushort*, and hard-cast it to char*, and then pass it to the string constructor, like so:
string asString;
unsafe
{
fixed (ushort *dataPtr = &data[0])
asString = new string((char *) dataPtr, 0, data.Length);
}
One thing you can do is switch from using a string to a stringBuilder it will help performance tremendously.
If you are willing to use unsafe code you can use pointers and implement the your c# code just like your c++. Or you could write a small c++\cli dll that implements this functionality.
Look into the Buffer class:
ushort[] theImageData = inImageData.DataArray;
byte[] buf = new byte[Buffer.ByteLength(theImageData)]; // 2 bytes per short
Buffer.BlockCopy(theImageData, 0, buf, 0, Buffer.ByteLength(theImageData));
string theOutData = System.Text.Encoding.ASCII.GetString(buf);
Just FYI, this has been fixed in later revision (gdcm 2.0.10). Look here:
http://gdcm.sourceforge.net/
-> http://apps.sourceforge.net/mediawiki/gdcm/index.php?title=GDCM_Release_2.0
I don't like this much, but it seems to work given the following assumptions:
1. Each ushort is an ASCII char between 0 and 127
2. (Ok, I guess there is just one assumption)
ushort[] data = inData; // The ushort array source
Byte[] bytes = new Byte[data.Length]; // Assumption - only need one byte per ushort
int i = 0;
foreach(ushort x in data) {
byte[] tmp = System.BitConverter.GetBytes(x);
bytes[i++] = tmp[0];
// Note: not using tmp[1] as all characters in 0 < x < 127 use one byte.
}
String str = Encoding.ASCII.GetString(bytes);
I'm sure there are better ways to do this, but it's all I could come up with quickly.
You can avoid unnecessary copying this way :
public static class Helpers
{
public static string ConvertToString(this ushort[] uSpan)
{
byte[] bytes = new byte[sizeof(ushort) * uSpan.Length];
for (int i = 0; i < uSpan.Length; i++)
{
Unsafe.As<byte, ushort>(ref bytes[i * 2]) = uSpan[i];
}
return Encoding.Unicode.GetString(bytes);
}
}