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Find and increment value in string of hex

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# 1  
Old 12-19-2017
Find and increment value in string of hex
I have a long string of hex (from ASN.1 data) where I need to find and change a particular hex value only and increment it. The hex pairs either side (84 and a7) of the value to increment will remain constant.

i.e. "84 <length> <value_to_increment> a7" starting with 00.

So end result:

Code:
840100a7
840101a7
...
84020080a7 (length changes to 02 when value reaches 80, 128dec)
84020081a7

Any ideas how best to do this?


Moderator's Comments:
Mod Comment Please use CODE tags (for data as well) as required by forum rules!
Last edited by RudiC; 12-19-2017 at 08:39 AM.. Reason: Added CODE tags.
# 2  
Old 12-19-2017
Code:
sed 's/84/\n84/g; s/a7/a7\n/g' infile | awk --non-decimal-data '
   /84[0-9][0-9]..*[aA]7/ {
      a=substr($0, 1, 4);
      b=substr($0, 5, length($0)-6);
      c=substr($0, length($0)-1);
      l=substr($0, 3, 2)*2;
      b=sprintf("%d", "0x" b); b=sprintf("%0*x", l, b+1)
      $0=a b c
   }
   {printf $0}
   '

Last edited by rdrtx1; 12-19-2017 at 11:19 AM..
# 3  
Old 12-19-2017
Not clear.
Do you have a string with above structure and want to produce a file from it, incrementing the value indicated line by line? Then, where to stop?
Or, do you have a file with above structured values in the lines, and want to just increment each line's value?
I guess, the value 0x7F needs special treatment, as the length has to be incremented, and the value will need four places, then?
# 4  
Old 12-19-2017
Sorry first poster trying to explain... Smilie

So I have a file containing one long line of hex (converted from BER ASN.1), i.e.

Code:
30820170a15c80070400020205010d8119877532221275e5727de311be4e938334297fb650ff00ff00ff82024e4ca31fa01580083033313035343030a2098107831341090000018102689582024e4c840100a70b80045940f1598103058390880102a282010ea4820...

I want to find all occurrences between the hex pairs 84 and a7 and replace these values by (length)(value) where length = 02 if value > 127dec, otherwise 01. And value should be incremented (beginning at 0) for each occurrence.

value will be equal to 2 bytes (4 places) where length = 02.
# 5  
Old 12-19-2017
Now, this is completely different from what you posted in #1. And, still not clear.
There's only one pattern occurrence in above sample, with value 00. That should become 01, understood. you don't say anything about the next pattern occurrence. Should that become 02 regardless of its initial value? Or, its initial value + 1? And, you didn't answer the question about the 0x7F value, should that ever occur.
# 6  
Old 12-19-2017
It's the same question but worded differently, appreciated it's still not clear though.

Ok, new example, original file:

Code:
30820170a15c800704000202050840100a710d8119877532221275e5727de31840100a71be4e938334297fb650ff00ff00ff820840100a724e4ca31fa01580083033313840100a7035343030a2098107831341090000018102689582024e4c840100a70b80045940f15981030583908

should become:

Code:
30820170a15c800704000202050840100a710d8119877532221275e5727de31840101a71be4e938334297fb650ff00ff00ff820840102a724e4ca31fa01580083033313840103a7035343030a2098107831341090000018102689582024e4c840104a70b80045940f15981030583908

So regardless of the initial value it should be replaced, beginning with
Code:
00

for the first occurrence and incremented for every occurrence thereafter.

Where value >
Code:
0x7F

the length (after the 84) will be set to
Code:
02

instead of
Code:
01

and the value will be 2 bytes (4 values) for example
Code:
84020080a7

Does that make sense? Thanks for trying to understand!
Last edited by securegooner; 12-19-2017 at 12:22 PM..
# 7  
Old 12-19-2017
Quote:
Originally Posted by securegooner
.
.
.
Where value >
Code:
0xF7

the length (after the 84) will be set to
Code:
02

instead of
Code:
01

and the value will be 2 bytes (4 values) for example
Code:
84020080a7

.
.
.

Why should 0xF7 be decremented to 0x80?
Last edited by RudiC; 12-19-2017 at 12:24 PM..
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