[Tcl-bugs] [ tcl-Bugs-1663473 ] binary scan seems to be losing bits

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Bugs item #1663473, was opened at 2007-02-19 05:35
Message generated for change (Comment added) made by hobbs
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Category: 12. ByteArray Object
Group: development: 8.5a6
>Status: Closed
>Resolution: Invalid
Priority: 5
Private: No
Submitted By: Larry W. Virden (lvirden)
Assigned to: Jeffrey Hobbs (hobbs)
Summary: binary scan seems to be losing bits

Initial Comment:
>From the man page for binary scan:

     b    The data is turned into a string of count binary digits in
          low-to-high order represented as a sequence of ``1'' and
          ``0'' characters.  The data bytes are scanned in first to
          last order with the bits being taken in low-to-high order
          within each byte.  Any extra bits in the last byte are
          ignored.  If count is *, then all of the remaining bits in
          string will be scanned.  If count is omitted, then one bit
          will be scanned.  For example,
               binary scan \x07\x87\x05 b5b* var1 var2
          will return 2 with 11100 stored in var1 and 1110000110100000
          stored in var2.


Perhaps I don't understand the meaning of the phrase "remaining bits in string".

It seems, to me, that this is a 24 bit string:
 % puts [string length  \x07\x87\x05 ]
 3
and as far as I know, on a sparc solaris machine, 3 bytes, times 8 bits per byte, should equal 24 bits.

 % binary scan \x07\x87\x05 b5b* var1 var2
2
 % puts $var1
11100
 % puts $var2
1110000110100000
% puts [string length $var1$var2]
21

Notice that 3 bits are missing. They are 000 from the first byte of the 3 bytes...

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>Comment By: Jeffrey Hobbs (hobbs)
Date: 2007-02-19 15:59

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Using tkcon:

(Tcl) 51 % binary scan \x07\x87\x05 b5b* var1 var2
2
(Tcl) 52 % binary scan \x07\x87\x05 b* var3
1
(Tcl) 53 % dump var var*
set ::var1 11100
set ::var2 1110000110100000
set ::var3 111000001110000110100000

You see that the missing 000 would be the first part of var2 - IOW,
extraneous bits.  I don't see a bug here.  The values are correct, it is
just that Tcl does format with all the preceding 0s.

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