Version 13 of Comp3 data conversion

Updated 2009-03-26 13:23:44 by jscottb

Function to convert comp3 packed decimal data (aka BCD) (see [L1 ]) to a string.

Note: This function assumes it's signed data.

 proc comp3tostring {packed_dec_data data_len} {
    set val 0
    set ret_sign {}

    for {set byte_ndx 0} {$byte_ndx < $data_len} {incr byte_ndx} {
       scan [string index $packed_dec_data $byte_ndx] %c byte
       set byte [format "%02.2x" $byte]
       if {$byte_ndx == [expr {$data_len - 1}]} {
          append val [format "%x" [string index $byte 0]]
          if {[string index $byte 1] == {d}} {
             set ret_sign {-}
          }
       } else {
          append val "[format "%x%x" [string index $byte 0] [string index $byte 1]]"
       }
    }

    return "$ret_sign$val"
 }

RS 2009-03-24: Here's a simpler alternative:

 proc comp3int x {
    binary scan $x H* hex
    scan $hex %d int; # make sure it's int size, else use '%ld' for longs.
    switch -- [string index $hex end] {
       c {}
       d {set int -$int}
       default {return -code error "bad comp3 number: $x"}
    }

    return $int
 }

Richard, after looking at the code again, I see you include the sign digit as part of the numbers value. This function would work fine on unsigned data but not signed. Made changes to make that one work.

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RS Of course it worked before I posted it... (tested with the examples on the page linked above). I use scan for two purposes: strip off leading zeroes except maybe a single one, and: stop parsing at the first non-decimal character (the last char can according to spec only be "c" or "d"). Demo:

 % scan 01234d %d
 1234

JSB Okay... I see my problem now. My function did not care about return data size. Your code worked for me on most data, but not all. After a quick look at the data in question, I see that it was failing on very large (a long) numbers (bad data, bad data!;). Changing the scan to a '%ld' made it work fine for me. Thanks!

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