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Re: How to encode/decode string of decimal digits

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David Brown <david.brown@hesbynett.no> wrote:
> On 21/10/15 17:53, pozz wrote:

(snip)
>> The strings are short, but not fixed-length. Here a small list of
>> examples of *different* strings:
>>   1234
>>   01234
>>   00001234
>>   123456789012345
>>   9874321
 
> The simple solution here would be to map decimal digits 0 to 9 to hex
> digits 0 to 9, and "space" or "no digit" to hex 'a'.  This would turn
> those strings into:
 
> 0xaaaaaaaaaaaa1234
> 0xaaaaaaaaaaa01234
> 0xaaaaaaaa00001234
> 0xa123456789012345
> 0xaaaaaaaaa9874321

As long as the numerical (binary) value isn't needed, such as
for arithmetic operations, I believe that this is the best choice.
(I might have used 0xf instead of 0xa, but it isn't much different.)

While sprintf() and strtoull() are easy to call, they are fairly
complicated functions, doing a lot of multiply and divide.
 
> Clear, simple, fast to implement and easy for debugging (since the hex
> values are human-readable).  Consider your packed strings as a uint64_t,
> and your comparisons are a simple uint64_t compare.  Depending on the
> speed of the flash on your particular Cortex-M0 chip, you might need
> something like 4 clock cycles per compare - that's about 100 µs to
> search through 1000 strings with a typical 48 MHz clock.  If that's
> sufficient, then you are done.

(snip)

-- glen

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Thread

How to encode/decode string of decimal digits pozz <pozzugno@gmail.com> - 2015-10-19 14:28 +0200
  Re: How to encode/decode string of decimal digits Bartc <bc@freeuk.com> - 2015-10-19 14:07 +0100
    Re: How to encode/decode string of decimal digits pozz <pozzugno@gmail.com> - 2015-10-19 15:58 +0200
      Re: How to encode/decode string of decimal digits Bartc <bc@freeuk.com> - 2015-10-19 15:22 +0100
      Re: How to encode/decode string of decimal digits Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-19 15:58 +0100
        Re: How to encode/decode string of decimal digits Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-19 22:28 +0100
  Re: How to encode/decode string of decimal digits Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-10-19 13:30 -0400
    Re: How to encode/decode string of decimal digits Robert Wessel <robertwessel2@yahoo.com> - 2015-10-19 16:18 -0500
      Re: How to encode/decode string of decimal digits Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-10-19 21:38 -0400
    Re: How to encode/decode string of decimal digits Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-10-20 08:00 +0000
  Re: How to encode/decode string of decimal digits Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-19 15:50 +0100
  Re: How to encode/decode string of decimal digits Keith Thompson <kst-u@mib.org> - 2015-10-19 09:01 -0700
  Re: How to encode/decode string of decimal digits Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-19 12:11 -0700
    Re: How to encode/decode string of decimal digits pozz <pozzugno@gmail.com> - 2015-10-20 13:51 +0200
      Re: How to encode/decode string of decimal digits Bartc <bc@freeuk.com> - 2015-10-20 13:38 +0100
        Re: How to encode/decode string of decimal digits glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-20 16:05 +0000
        Re: How to encode/decode string of decimal digits pozz <pozzugno@gmail.com> - 2015-10-21 09:29 +0200
          Re: How to encode/decode string of decimal digits Bartc <bc@freeuk.com> - 2015-10-21 11:27 +0100
            Re: How to encode/decode string of decimal digits pozz <pozzugno@gmail.com> - 2015-10-21 17:55 +0200
          Re: How to encode/decode string of decimal digits Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-10-21 08:03 -0400
            Re: How to encode/decode string of decimal digits pozz <pozzugno@gmail.com> - 2015-10-21 17:53 +0200
              Re: How to encode/decode string of decimal digits supercat@casperkitty.com - 2015-10-21 09:37 -0700
              Re: How to encode/decode string of decimal digits David Brown <david.brown@hesbynett.no> - 2015-10-22 11:47 +0200
                Re: How to encode/decode string of decimal digits pozz <pozzugno@gmail.com> - 2015-10-22 13:44 +0200
                Re: How to encode/decode string of decimal digits Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-22 13:45 +0100
                Re: How to encode/decode string of decimal digits Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-22 15:51 +0100
                Re: How to encode/decode string of decimal digits supercat@casperkitty.com - 2015-10-22 09:31 -0700
                Re: How to encode/decode string of decimal digits Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-22 20:48 +0100
                Re: How to encode/decode string of decimal digits pozz <pozzugno@gmail.com> - 2015-10-23 10:14 +0200
                Re: How to encode/decode string of decimal digits Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-23 11:14 +0100
                Re: How to encode/decode string of decimal digits Bartc <bc@freeuk.com> - 2015-10-23 11:47 +0100
                Re: How to encode/decode string of decimal digits Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-23 13:22 +0100
                Re: How to encode/decode string of decimal digits David Brown <david.brown@hesbynett.no> - 2015-10-22 15:07 +0200
                Re: How to encode/decode string of decimal digits glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-22 22:05 +0000
                Re: How to encode/decode string of decimal digits pozz <pozzugno@gmail.com> - 2015-10-23 10:15 +0200
  Re: How to encode/decode string of decimal digits glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-19 22:02 +0000
  Re: How to encode/decode string of decimal digits supercat@casperkitty.com - 2015-10-20 10:09 -0700

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