Re: [rfa] Clarify remote protocol RLE example

Daniel Jacobowitz
2007-12-16T20:30:49Z

On Sun, Nov 04, 2007 at 06:02:44AM +0200, Eli Zaretskii wrote:
> Sorry, I now realize that I misunderstood the reason why you used the
> "initial character". You meant the repeated character itself, right?
>
> Then how about this variant:
>
> Run-length encoding replaces runs of identical characters with one
> instance of the repeated character, followed by a @samp{*} and a
> repeat count.

When I put everything together, I came up with the attached patch. Is
this clearer?

--
Daniel Jacobowitz
CodeSourcery

2007-12-16 Daniel Jacobowitz <dan@codesourcery.com>

* gdb.texinfo (Overview): Clarify run-length encoding
example. Remove the restriction on "+" and "-" characters.

Index: gdb.texinfo
===================================================================
RCS file: /cvs/src/src/gdb/doc/gdb.texinfo,v
retrieving revision 1.449
diff -u -p -r1.449 gdb.texinfo
--- gdb.texinfo 15 Dec 2007 13:13:12 -0000 1.449
+++ gdb.texinfo 16 Dec 2007 20:28:44 -0000
@@ -23158,20 +23158,24 @@ must also escape @code{0x2a} (@sc{ascii}
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{$}, @samp{#}, @samp{+} and @samp{-} or with a numeric
-value greater than 126 should not be used.
-
-So:
-@smallexample
-"@code{0* }"
-@end smallexample
-@noindent
-means the same as "0000".
+Response @var{data} can be run-length encoded to save space.
+Run-length encoding replaces runs of identical characters with one
+instance of the repeated character, followed by a @samp{*} and a
+repeat count. The repeat count is itself sent encoded, to avoid
+binary characters in @var{data}: a value of @var{n} is sent as
+@code{@var{n}+29}. For a repeat count greater or equal to 3, this
+produces a printable @sc{ascii} character, e.g.@: a space (@sc{ascii}
+code 32) for a repeat count of 3. (This is because run-length
+encoding starts to win for counts 3 or more.) Thus, for example,
+@samp{0* } is a run-length encoding of ``0000'': the space character
+after @samp{*} means repeat the leading @code{0} @w{@code{32 - 29 =
+3}} more times.
+
+The printable characters @samp{#} and @samp{$} 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.