I have a unsigned data representation like this:
val str = "145 38 0 255 0 1"
I want to now get this unsigned representation as a byteString after which I can manipulate on the individual bits to extract information. So basically what I want is to get the unsigned version.
For example., the unsigned binary representation of 145 is 10010001, but the signed version is -00000111.
scala> 145.byteValue
res128: Byte = -111 // I would need an unsigned value instead!
So is there a function or an approach to convert the 145 to an unsigned representation?
Signed and unsigned bytes (or Ints or Longs) are just two different ways to interpret the same binary bits.
In signed bytes the first bit from the left (most significant bit) is interpreted as the sign.
0 means positive, 1 means negative.
For negative numbers, what comes after the minus sign is 256 - unsigned-value.
So in your case what we get is 256 - 145 = 111.
Java / Scala bitwise operators work on the underlying bits, not on the signed/unsigned representation, but of course the results, when printed are still interpreted as signed.
Actually, to save on confusion, I would just work with Ints (or Shorts).
But it will work just as well with bytes.
For example to get the n-th bit you could do something like:
def bitValue(byte: Byte, n: Byte) = {
val pow2 = Math.pow(2, n - 1).toInt
if((pow2 & byte) == 0) 0
else 1
}
bitValue(145.byteValue, 8)
res27: Int = 1
Related
I am trying to convert a (variable length) Hex String to Signed Integer (I need either positive or negative values).
[Int16] [int 32] and [int64] seem to work fine with 2,4+ byte length Hex Strings but I'm stuck with 3 byte strings [int24] (no such command in powershell).
Here's what I have now (snippet):
$start = $mftdatarnbh.Substring($DataRunStringsOffset+$LengthBytes*2+2,$StartBytes*2) -split "(..)"
[array]::reverse($start)
$start = -join $start
if($StartBytes*8 -le 16){$startd =[int16]"0x$($start)"}
elseif($StartBytes*8 -in (17..48)){$startd =[int32]"0x$($start)"}
else{$startd =[int64]"0x$($start)"}
With the above code, a $start value of "D35A71" gives '13851249' instead of '-2925967'. I tried to figure out a way to implement two's complement but got lost. Any easy way to do this right?
Thank you in advance
Edit: Basically, I think I need to implement something like this:
int num = (sbyte)array[0] << 16 | array[1] << 8 | array[2];
as seen here.
Just tried this:
$start = "D35A71"
[sbyte]"0x$($start.Substring(0,2))" -shl 16 -bor "0x$($start.Substring(2,2))" -shl 8 -bor "0x$($start.Substring(4,2))"
but doesn't seem to get the correct result :-/
To parse your hex.-number string as a negative number you can use [bigint] (System.Numerics.BigInteger):
# Since the most significant hex digit has a 1 as its most significant bit
# (is >= 0x8), it is parsed as a NEGATIVE number.
# To force unconditional interpretation as a positive number, prepend '0'
# to the input hex string.
PS> [bigint]::Parse('D35A71', 'AllowHexSpecifier')
-2925967
You can cast the resulting [bigint] instance back to an [int] (System.Int32).
Note:
The result is a negative number, because the most significant hex digit of the hex input string is >= 0x8, i.e. has its high bit set.
To force [bigint] to unconditionally interpret a hex. input string as a positive number, prepend 0.
The internal two's complement representation of a resulting negative number is performed at byte boundaries, so that a given hex number with an odd number of digits (i.e. if the first hex digit is a "half byte") has the missing half byte filled with 1 bits.
Therefore, a hex-number string whose most significant digit is >= 0x8 (parses as a negative number) results in the same number as prepending one or more Fs (0xF == 1111) to it; e.g., the following calls all result in -2048:
[bigint]::Parse('800', 'AllowHexSpecifier'),
[bigint]::Parse('F800', 'AllowHexSpecifier'),
[bigint]::Parse('FF800', 'AllowHexSpecifier'), ...
See the docs for details about the parsing logic.
Examples:
# First digit (7) is < 8 (high bit NOT set) -> positive number
[bigint]::Parse('7FF', 'AllowHexSpecifier') # -> 2047
# First digit (8) is >= 8 (high bit IS SET) -> negative number
[bigint]::Parse('800', 'AllowHexSpecifier') # -> -2048
# Prepending additional 'F's to a number that parses as
# a negative number yields the *same* result
[bigint]::Parse('F800', 'AllowHexSpecifier') # -> -2048
[bigint]::Parse('FF800', 'AllowHexSpecifier') # -> -2048
# ...
# Starting the hex-number string with '0'
# *unconditionally* makes the result a *positive* number
[bigint]::Parse('0800', 'AllowHexSpecifier') # -> 2048
I need to convert the given text (not in file format) into binary values and store in a single array that is to be given as input to other function in Matlab .
Example:
Hi how are you ?
It is to be converted into binary and stored in an array.I have used dec2bin() function but i did not suceed in getting the output required.
Sounds a bit like a trick question. In MATLAB, a character array (string) is just a different representation of 16-bit unsigned character codes.
>> str = 'Hi, how are you?'
str =
Hi, how are you?
>> whos str
Name Size Bytes Class Attributes
str 1x16 32 char
Note that the 16 characters occupy 32 bytes, or 2 bytes (16-bits) per character. From the documentation for char:
Valid codes range from 0 to 65535, where codes 0 through 127 correspond to 7-bit ASCII characters. The characters that MATLAB® can process (other than 7-bit ASCII characters) depend upon your current locale setting. To convert characters into a numeric array,use the double function.
Now, you could use double as it recommends to get the character codes into double arrays, but a minimal representation would simply involve uint16:
int16bStr = uint16(str)
To split this into bytes, typecast into 8-bit integers:
typecast(int16bStr,'uint8')
which yields 32 uint8 values (bytes), which are suitable for conversion to binary representation with dec2bin, if you want to see the binary (but these arrays are already binary data).
If you don't expect anything other than ASCII characters, just throw out the extra bits from the start:
>> int8bStr =
72 105 44 32 104 111 119 32 97 114 101 32 121 111 117 63
>> binStr = reshape(dec2bin(binStr8b.'),1,[])
ans =
110011101110111001111111111111110000001001001011111011000000 <...snip...>
I am looking for a way to convert an array of 16-bit unsigned integer into ASCII char array. I am using char to do the conversion
D=[65 65 65 65];
char(D)
which will show 4 'A'. However, since each number in D is 16-bit, I expect it to convert each number to 2 chars. For example, if I have
D=[16707]
char(D)
I expect it gives me two chars 'A' and 'C'. But char always return 1 character. Is that anyway to force char to convert like the way I stated? Thanks.
For this, you need to write your own function.
You can use char() to convert most significant byte and least significant byte separately.
k = 16707;
first = char(bitand(bitshift(k, -8), 255));
second = char(bitand(k, 255));
Have a look at
http://www.mathworks.com/help/matlab/ref/char.html
It cleatly states that the char function is valid only for 8 bit numbers. you can convert each part of cell of the array with this and contact the results for each two cells.
Use typecast to convert each uint16 to two uint8, and then apply char. Make sure that the input to typecastr is really of type uint16.
If you need to reverse char order, use swapbytes on the uint16 vector.
>> D = [16707 16708];
>> char(typecast(uint16(D),'uint8'))
ans =
CADA
>> char(typecast(swapbytes(uint16(D)),'uint8'))
ans =
ACAD
I am working on a small task which requires some base64 encoding. I am trying to do it in head but getting lost .
I have a 13 digit number in java long format say: 1294705313608 , 1294705313594 , 1294705313573
I do some processing with it, bascially I take this number append it with stuff put it in a byte array and then convert it to base64 using:
String b64String = new sun.misc.BASE64Encoder().encodeBuffer(bArray);
Now , I know that for my original number, the first 3 digits would never change. So 129 is constant in above numbers. I want to find out how many chars corresponding to those digits would not change in the resultant base64 string.
Code to serialize long to the byte array. I ignore the first 2 bytes since they are always 0:
bArray[0] = (byte) (time >>> 40);
bArray[1] = (byte) (time >>> 32);
bArray[2] = (byte) (time >>> 24);
bArray[3] = (byte) (time >>> 16);
bArray[4] = (byte) (time >>> 8);
bArray[5] = (byte) (time >>> 0);
Thanks.
Notes:
I know that base64 would take 6 bits and make one character out of it. So if first 3 digits do not change in long how many chars would not change in base64.
This in NOT a HW assignment, but I am not very familiar with encoding.
1290000000000 is 10010110001011001111111011110010000000000 in binary.
1299999999999 is 10010111010101110000010011100011111111111 in binary.
Both are 41 bits long, and they differ after the first 7 bits. Your shift places bits 41-48 in the first byte, which will always be 00000001. The following byte will always be 00101110, 00101101, or 00101110. So you've got the leading 14 bits in common across all your possible array values, which (at 6 bits per encoded base64 char) means 2 characters in common in the encoded string.
Appears you're on the right track. I think what you want to do is convert a long to a byte array, then convert the byte array to Base64.
How do I convert Long to byte[] and back in java shows you how to convert it to bytes.
Does anyone have a code snippet or a class that will take a long long and turn it into a 16 byte Hex string?
I'm looking to turn data like this
long long decimalRepresentation = 1719886131591410351;
and turn it into this
//Base 16 Hex Output: 17DE435307A07300
The %x operator doesn't want to work for me
NSLog(#"Hex: %x",decimalRepresentation);
//console : "Hex: 7a072af"
As you can see that's not even close. Any help is truly appreciated!
%x prints an unsigned integer in hexadecimal representation and sizeof(long long) != sizeof(unsigned). See e.g. "Data Type Size and Alignment" in the 64bit transitioning guide.
Use the ll specifier (thats two lower-case L) to get the desired output:
NSLog(#"%llx", myLongLong);