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* gdb.texinfo (Overview): Clarify run-length encoding

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example.  Remove the restriction on "+" and "-" characters.
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Daniel Jacobowitz
2007-12-16 22:57:06 +00:00
parent c162e8c9a4
commit 1d3811f649
2 changed files with 22 additions and 13 deletions
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gdb/doc/ChangeLog
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@ -1,3 +1,8 @@
2007-12-16 Daniel Jacobowitz <dan@codesourcery.com>
* gdb.texinfo (Overview): Clarify run-length encoding
example. Remove the restriction on "+" and "-" characters.
2007-12-15 Eli Zaretskii <eliz@gnu.org>
* gdb.texinfo (Host I/O Packets): Fix xref syntax.

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gdb/doc/gdb.texinfo
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@ -23158,20 +23158,24 @@ must also escape @code{0x2a} (@sc{ascii} @samp{*}), so that it
is not interpreted as the start of a run-length encoded sequence
(described next).
Response @var{data} can be run-length encoded to save space. A @samp{*}
means that the next character is an @sc{ascii} encoding giving a repeat count
which stands for that many repetitions of the character preceding the
@samp{*}. The encoding is @code{n+29}, yielding a printable character
where @code{n >=3} (which is where rle starts to win). The printable
characters @samp{$}, @samp{#}, @samp{+} and @samp{-} or with a numeric
value greater than 126 should not be used.
Response @var{data} can be run-length encoded to save space.
Run-length encoding replaces runs of identical characters with one
instance of the repeated character, followed by a @samp{*} and a
repeat count. The repeat count is itself sent encoded, to avoid
binary characters in @var{data}: a value of @var{n} is sent as
@code{@var{n}+29}. For a repeat count greater or equal to 3, this
produces a printable @sc{ascii} character, e.g.@: a space (@sc{ascii}
code 32) for a repeat count of 3. (This is because run-length
encoding starts to win for counts 3 or more.) Thus, for example,
@samp{0* } is a run-length encoding of ``0000'': the space character
after @samp{*} means repeat the leading @code{0} @w{@code{32 - 29 =
3}} more times.
So:
@smallexample
"@code{0* }"
@end smallexample
@noindent
means the same as "0000".
The printable characters @samp{#} and @samp{$} or with a numeric value
greater than 126 must not be used. Runs of six repeats (@samp{#}) or
seven repeats (@samp{$}) can be expanded using a repeat count of only
five (@samp{"}). For example, @samp{00000000} can be encoded as
@samp{0*"00}.
The error response returned for some packets includes a two character
error number. That number is not well defined.