Re: relearning C: why does an in-place change to a char* segfault?

On 8/3/24 10:58 PM, Keith Thompson wrote:
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Lawrence D'Oliveiro <ldo@nz.invalid> writes:
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On Sat, 03 Aug 2024 17:07:37 -0700, Keith Thompson wrote:
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... general compression isn't something I've seen ...

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I recall Apple had a patent on some aspects of the ?PEF?
executable format that they created for their PowerPC machines
running old MacOS.  This had to do with some clever instruction
encodings for loading stuff into memory.

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Is that relevant to what I asked about?
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What I had in mind is something that, given this:
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     static int buf = { 1, 1, 1, ..., 1 }; // say, 1000 elements
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would store something less than 1000*sizeof(int) bytes in the
executable file.  I wouldn't be hard to do, but I'm not convinced
it would be worthwhile.

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I vaguely seem to remember an embedded format that did something like
this.  The .init segement that was "copied" to the .data segement has
a simple run-length encoding option.  For non-repetitive data, it
just encoded 1 copy of length n.  But it could also encode repeats
like your example.  When EPROM was a scarce commodity squeezing out a
bit of size for the .init segment was useful.
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My guess that since it didn't persist, it didn't actually help that
much.