http://simonwillison.net/2024-05-08T14:23:13+00:00Simon Willison2024-05-08T14:23:13+00:002024-05-08T14:23:13+00:00https://simonwillison.net/2024/May/8/tagged-pointer-strings-2015/#atom-tag

<p><strong><a href="https://mikeash.com/pyblog/friday-qa-2015-07-31-tagged-pointer-strings.html">Tagged Pointer Strings (2015)</a></strong></p> Mike Ash digs into a fascinating implementation detail of macOS.</p> <p>Tagged pointers provide a way to embed a literal value in a pointer reference. Objective-C pointers on macOS are 64 bit, providing plenty of space for representing entire values. If the least significant bit is 1 (the pointer is a 64 bit odd number) then the pointer is "tagged" and represents a value, not a memory reference.</p> <p>Here's where things get really clever. Storing an integer value up to 60 bits is easy. But what about strings?</p> <p>There's enough space for three UTF-16 characters, with 12 bits left over. But if the string fits ASCII we can store 7 characters.</p> <p>Drop everything except <code>a-z A-Z.0-9</code> and we need 6 bits per character, allowing 10 characters to fit in the pointer.</p> <p>Apple take this a step further: if the string contains just <code>eilotrm.apdnsIc ufkMShjTRxgC4013</code> ("b" is apparently uncommon enough to be ignored here) they can store 11 characters in that 60 bits! <p><small></small>Via <a href="https://lobste.rs/s/5417dx/storing_data_pointers#c_noslq0">Lobste.rs</a></small></p> <p>Tags: <a href="https://simonwillison.net/tags/c">c</a>, <a href="https://simonwillison.net/tags/objective-c">objective-c</a>, <a href="https://simonwillison.net/tags/strings">strings</a></p>

2019-03-09T18:29:13+00:002019-03-09T18:29:13+00:00https://simonwillison.net/2019/Mar/9/datasette-jellyfish/#atom-tag

<p><strong><a href="https://github.com/simonw/datasette-jellyfish">datasette-jellyfish</a></strong></p> I learned about a handy Python library called Jellyfish which implements approximate and phonetic matching of strings—soundex, metaphone, porter stemming, levenshtein distance and more. I’ve built a simple Datasette plugin which wraps the library and makes each of those algorithms available as a SQL function. <p>Tags: <a href="https://simonwillison.net/tags/strings">strings</a>, <a href="https://simonwillison.net/tags/datasette">datasette</a></p>

2019-02-22T15:27:31+00:002019-02-22T15:27:31+00:00https://simonwillison.net/2019/Feb/22/string-length-rosetta-code/#atom-tag

<p><strong><a href="https://www.rosettacode.org/wiki/String_length">String length - Rosetta Code</a></strong></p> Calculating the length of a string is surprisingly difficult once Unicode is involved. Here's a fascinating illustration of how that problem can be attached dozens of different programming languages. From that page: the string <code>"J̲o̲s̲é̲"</code> (<code>"J\x{332}o\x{332}s\x{332}e\x{301}\x{332}"</code>) has 4 user-visible graphemes, 9 characters (code points), and 14 bytes when encoded in UTF-8. <p><small></small>Via <a href="https://twitter.com/jeffsonstein/status/1098927304124841984">@jeffsonstein</a></small></p> <p>Tags: <a href="https://simonwillison.net/tags/programming-languages">programming-languages</a>, <a href="https://simonwillison.net/tags/strings">strings</a>, <a href="https://simonwillison.net/tags/unicode">unicode</a></p>

2007-10-09T02:08:13+00:002007-10-09T02:08:13+00:00https://simonwillison.net/2007/Oct/9/strings/#atom-tag

<p><strong><a href="http://pyside.blogspot.com/2007/10/string-types-in-python-3.html">String types in Python 3</a></strong></p> bytes are now immutable (just like the bytestrings they are replacing) and a new mutable buffer type has been introduced. <p>Tags: <a href="https://simonwillison.net/tags/buffers">buffers</a>, <a href="https://simonwillison.net/tags/bytes">bytes</a>, <a href="https://simonwillison.net/tags/bytestrings">bytestrings</a>, <a href="https://simonwillison.net/tags/python">python</a>, <a href="https://simonwillison.net/tags/python3">python3</a>, <a href="https://simonwillison.net/tags/strings">strings</a>, <a href="https://simonwillison.net/tags/unicode">unicode</a></p>

2007-09-14T08:17:05+00:002007-09-14T08:17:05+00:00https://simonwillison.net/2007/Sep/14/lshift/#atom-tag

<p><strong><a href="http://www.lshift.net/blog/2007/09/13/how-should-json-strings-be-represented-in-erlang">How should JSON strings be represented in Erlang?</a></strong></p> Erlang’s poor support for strings makes this a surprisingly tricky question. <p>Tags: <a href="https://simonwillison.net/tags/erlang">erlang</a>, <a href="https://simonwillison.net/tags/json">json</a>, <a href="https://simonwillison.net/tags/strings">strings</a>, <a href="https://simonwillison.net/tags/tonygarnockjones">tonygarnockjones</a></p>