I have an AIR application that reads RFID tags. The values of the tag ID's are 7 byte hex values.
There is a limitation on the highest numbers represented accurately within actionscript.
The Number type only works with 53 bit values. The 7byte hex value is 56 bit.
So there is a chance of possibly duplicate keys.
Is there any advantage in using the HEX values themselves as keys for the dictionary?
Or does Flash internally still convert these values to Numbers before using as keys?
You are right about this limitation, as3 Number type is actually a Double precision 64-bit with only 53 bits for the mantissa, but I wonder how do you read the 7 byte value and where do you store it?
There are several as3 Long implementations (64 Integer) so you can use it to read and store 7 bit number (but it will still read 8 bytes from the ByteArray), but if you don't need the Math for your big number just use Strings to read in and use them as a keys for Dictionary.
Anyway Dictionary uses only Strings or Objects as a keys but not Numbers, so even if as3 had a Long it would be convert to the String.
Related
I have to handle huge binary numbers (<=4096 digits) - what is the best way to handle such big numbers? I have to multiply them afterward and apply the %-operation on these numbers.
Do I have to use structs or how am I supposed to handle such data?
If you've got it as a string of 4096 digit, you can convert it into a list with separate smaller chunks (eg into bytes each consisting of 8 bits), then if you need to multiply/apply the %-operation on these numbers, you probably will need create a function that converts those "chunks" from binary to denary (so you can multiply them and so on.)
I am new to dynamo db binary data. I have a hash key + range key(both are byte[]). Now I am trying to get a list of items by querying on range key(ex: le, ge or between). I am able to do put and get operations fine.
However I am getting errors while doing this. My question is can dynamodb do this comparison? I am passing a byte[]. Can dynamodb check if existing rangekey(byte[]) is lesser or greater than this?
Yes, DynamoDB does support the byte array type well, and also allows comparison between them in conditions, done lexicographically, so what you want to do should and does work.
You didn't say which "errors" you are getting. You should be aware that DynamoDB treats the bytes of the byte arrays as unsigned bytes. For example, the byte 128 comes after byte 127. I don't know which language you are using to test this, but some languages have signed bytes - meaning that the byte 128 is treated as "-1" and will come before, not after, byte 127 in the sort order. DynamoDB doesn't do that, because it uses unsigned bytes.
My instructor stated that "an octal byte consists of 6 bits". I am having difficulty understanding why this is, as an octal digit consists of 3 binary bits. I also do not understand the significance of an octal byte being defined as '6 bits' as opposed to some other number.
Can anyone explain why this is, if it is in fact true, or point me to a useful explanation?
This is all speculation and guesswork, since none of this is in any way standard terminology.
An 8-bit byte can be written as two digits of hexadecimals, because each digit expresses 4 bits. The largest such byte value is 0xFF.
By analogy, two digits of octals can express 2 × 3 = 6 bits. Its largest value is 077. So if you like you can call a pair of two octals an "octal byte", but only if you will also call an 8-bit byte a "hexadecimal byte".
In my personal opinion neither notion is helpful or useful, and you'd be best of just to say how many bits your byte has.
Like #Kerrek SB I'd have to guess the same.
Tell him an octal byte is two octal nibbles, that should sort him out.
Two hexadecimal digits is an 8 bit byte, so each four bits were called a nibble.
as for wiki : The byte is a unit of digital information that most commonly consists of 8 bits. The bit is a contraction of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represented as either "1" or "0".
so byte is a set of bunch of bits. to be specific of 8 bits.
we see that the definition doesnt say anything about dec oct hex and other notations of integer number.
indeed byte and integer number is not the same. so where
does it start ?
if we type bits of byte like so 01001010 we can find that
we can map 1-to-1 this object to binary notation
of integer numbers 01001010.
(byte)01001010 --> (binary integer) 01001010
the two objects look the same but actually is just mapping.
now we work with integer number instead of abstract object "byte". an integer
number can be designated via different notations like : dec, binary, hex, oct etc.
notation like octal(hex,dec etc) is just a method of designation of integer number. it does not influence the nature of initial byte object.
byte has 8 bits whatever notation is used.
ISO/IEC 2382-1:1993 says:
1.The number of bits in a byte is usually 8.
2.Octet is Byte that consists of eight
Bits
We are learning about converting Binary to Decimal (and vice-versa) as well as other base-conversion methods, but I don't understand the necessity of this knowledge.
Are there any real-world uses for converting numbers between different bases?
When dealing with Unicode escape codes— '\u2014' in Javascript is — in HTML
When debugging— many debuggers show all numbers in hex
When writing bitmasks— it's more convenient to specify powers of two in hex (or by writing 1 << 4)
In this article I describe a concrete use case. In short, suppose you have a series of bytes you want to transfer using some transport mechanism, but you cannot simply pass the payload as bytes, because you are not able to send binary content. Let's say you can only use 64 characters for encoding the payload. A solution to this problem is to convert the bytes (8-bit characters) into 6-bit characters. Here the number conversion comes into play. Consider the series of bytes as a big number whose base is 256. Then convert it into a number with base 64 and you are done. Each digit of the new base 64 number now denotes a character of your encoded payload...
If you have a device, such as a hard drive, that can only have a set number of states, you can only count in a number system with that many states.
Because a computer's byte only have on and off, you can only represent 0 and 1. Therefore a base2 system is used.
If you have a device that had 3 states, you could represent 0, 1 and 2, and therefore count in a base 3 system.
I have created an SQL database using Java. I have a table created which has two columns, the first being a big integer which increments, the second I have tried defining it as a char, varchar and binary.
But I'm still not getting the desired functionality. Say I try and store a hex number 0a into the char column and I get an error. I appended 0x to the beginning and it seems to store, but when I print out the contents it is blank. Or in some cases I get characters such as '/' or '?'. I also tried using SQL explorer and it gives me the same result viewing the table,
My problem is I need to store an eight character hex string such as eb8d4ee6.
Could someone please advise me of how this can be done?
See http://dev.mysql.com/doc/refman/5.5/en/hexadecimal-literals.html
MySQL supports hexadecimal values,
written using X'val', x'val', or 0xval
format, where val contains hexadecimal
digits (0..9, A..F). Lettercase of the
digits does not matter. For values
written using X'val' or x'val' format,
val must contain an even number of
digits. For values written using 0xval
syntax, values that contain an odd
number of digits are treated as having
an extra leading 0. For example, 0x0a
and 0xaaa are interpreted as 0x0a and
0x0aaa.
In numeric contexts, hexadecimal
values act like integers (64-bit
precision). In string contexts, they
act like binary strings, where each
pair of hex digits is converted to a
character:
You probably should store the Hex number in an integer column. You can then convert back to hex when selecting using the HEX() function.
E.g.,
INSERT INTO MyTable (`MyIntegerColumn`) VALUES (0xeb8d4ee6);
You can use a Json column:
And use JSON.stringify(hex) to insert and you can always get the result via select and compare too