CODEWITHSUNDEEP
pythonarrayshex
Thor Peterson
Thor Peterson

Reputation: 131

How to address indicies in an array using HEX

I have a file that I read lines from and manipulate the strings.

Here is an example of a few of the lines (the file is Intel's HEX format if you're interested):

:10DE50003EDE179280DB0338D2C32202023CD2D3CB
:10DE600022021792A0DB0338E2C32202023CE2D373
:10DE7000220292533EDEB0906400C4FF022082432F
:10DE80003EDE3741324190C3B8240013FDDBFF056D
:10DE900057494D453420D0D88CDEFDDB8FDEFF03A3

A buddy suggested I create an array with the first 4:7 bytes as the index, EG, DE50, then use the remaining 16 bytes as the data (00 after DE50 is not used, and last byte is not used). He said I could use HEX and add let's say, 10 to the DE50 to get DE5A and therefore locate the byte associated with that index. Problem is, I can't figure out a way to do that. Is it even possible? This would allow me to then address any byte I want by knowing the HEX index which would be really powerful.

Thank you!

Upvotes: 0

Views: 1895

Answers (2)

abarnert
abarnert

Reputation: 365925

You're on the right track here, but you can't have an "array" indexed by hex characters. Arrays, and lists, are always indexed by integers, starting with 0.

If you know the initial offset (which you do, from the first line), you can make an index very easily. For example, everything from 'DE50' to 'DE5F' should be line #0, right? So, convert that DE50 to an integer, divide by 16 (truncating fractions), and subtract 0xDE50. Like this:

with open('hexfile.txt') as f:
    lines = list(f)
offset = int(lines[0][4:7], 16) // 16

def get_line(hex_index):
    index = int(hex_index, 16) // 16
    return lines[index - offset]

Alternatively, you could use a dict keyed off the hex indices, instead of a list, and then do what your friend suggested:

with open('hexfile.txt') as f:
    lines = {line[4:7]: line for line in f}

def get_line(hex_index):
    base_hex_index = hex_index[:3] + '0'
    return lines[base_hex_index]

However, this seems to be just adding extra complexity to your data structure for no benefit. If you've got sequential lines, just treat them sequentially. And if you've got numbers as hex strings, just convert them to numbers to treat them as indices.

Upvotes: 1

John La Rooy
John La Rooy

Reputation: 304375

There is an Intel Hex package in pypi perhaps you should look at that first

Here are some examples copied from the docs.

Once created, an IntelHex object can be loaded with data. This is only necessary if “source” was unspecified in the constructor. You can also load data several times (but if addresses in those files overlap you get exception AddressOverlapError). This error is only raised when reading from hex files. When reading from other formats, without explicitly calling merge, the data will be overwritten. E.g.:

>>> from intelhex import IntelHex
>>> ih = IntelHex()                     # create empty object
>>> ih.loadhex('foo.hex')               # load from hex
>>> ih.loadfile('bar.hex',format='hex') # also load from hex
>>> ih.fromfile('bar.hex',format='hex') # also load from hex

NOTE: using IntelHex.fromfile is recommended way.

All of the above examples will read from HEX files. IntelHex also supports reading straight binary files. For example:

>>> from intelhex import IntelHex
>>> ih = IntelHex()                     # create empty object
>>> ih.loadbin('foo.bin')               # load from bin
>>> ih.fromfile('bar.bin',format='bin') # also load from bin
>>> ih.loadbin('baz.bin',offset=0x1000) # load binary data and place them
>>>                                     # starting with specified offset

Finally, data can be loaded from an appropriate Python dictionary. This will permit you to store the data in an IntelHex object to a builtin dictionary and restore the object at a later time. For example:

>>> from intelhex import IntelHex
>>> ih = IntelHex('foo.hex') # create empty object
>>> pydict = ih.todict()     # dump contents to pydict
...do something with the dictionary...

>>> newIH = IntelHex(pydict) # recreate object with dict
>>> another = IntelHex()     # make a blank instance
>>> another.fromdict(pydict) # now another is the same as newIH

Upvotes: 2

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