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  3. Oct 31, 2020
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  13. Sep 27, 2020
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  17. Aug 22, 2020
    • Antonio Cardace's avatar
      docs: remove generation of "Last updated" field · f5546ef7
      Antonio Cardace authored 
      The generation of this field makes the resulting Tcl.html different between builds,
as it records the time of generation, remove this as it causes jimtcl rpms for different
arches (on RHEL/Fedora) to have a file conflict on Tcl.html.
      f5546ef7
  19. Jul 31, 2020
  21. Jul 24, 2020
  23. Jul 12, 2020
  25. Jun 25, 2020
    • Steve Bennett's avatar
      docs: use "empty string" instead of "null string" · 4e2cdaca
      Steve Bennett authored 
      

Avoid ambiguity re null characters

Signed-off-by: default avatarSteve Bennett <steveb@workware.net.au>
      4e2cdaca
    • Steve Bennett's avatar
      core: dicts (and arrays) now preserve insertion order · 99b7ce97
      Steve Bennett authored 
      

Although the documentation has always stated that, like Tcl,
insertion order of dictionaries was preserved, this has never
been the case. Instead, dictionaries were implemented as simple
hash tables that did not preserve order.

Now, a new implementation of dictionaries preserves insertion
order and has a number of other benefits.

Instead of hashing keys and storing keys and values in the hash table,
the keys and values are not stored in a separate table, exactly as
lists are stored, with alternating key, value pairs. Iterating over the
dictionary is exactly like iterating over a list, where the order is consistent.

The hash table uses closed hashing rather than open hashing to avoid
allocatation of hash entry structures. Instead a fixed (but expandable)
hash table maps the key hash to the offset in the key/value table.
This use of offsets means that if the key/value table grows, the offsets
remain valid. Likewise, if the hash table needs to grow, the key, value table
remains unchanged.

In addition to the offset (which indexes to the value, and 0 means the hash table entry is unused),
the original hash is stored in the hash table. This reduces the need for object
comparisons on hash entry collisions.

The collision resolution algorithm is the same as that used by Python:

    peturb >>= 5;
    idx = (5 * idx + 1 + peturb) & dict->sizemask;

In order to reduce collisions, the hash table is expanded once it reaches
half full. This is more conservative that Python where the table is expanded
when it is two thirds full.

Note that if a hash collision occurs and then the original entry
that cased the hash collision is removed, we still need to continue
iterating when searching for the new key. Don't stop at the now-empty
slot.  So these entries are marked with offset=-1 to indicate that
they need to be skipped.

In addition, the new faster hashing algorithm from Tcl 8.7 is used.
This the hash for integers to be calculated efficiently without requiring
them to be converted to string form first.

This implementation is modelled largely on the Python dict implementation.

Overall the performance should be an improvement over the current implementation,
whilst preserving order. Dictionary creating and insertion should be faster
as hash entries do not need to be allocated and resizing should be slightly faster.
Entry lookup should be about the same, except may be faster for pure integer keys.

Below are some indicative benchmarks.

                                                    OLD     NEW
dict-create-1.1  Create empty dict               97.2ns       .
dict-create-1.2  Create small dict                440ns    -27%
dict-create-1.3  Create medium dict              1.54us    -57%
dict-create-1.4  Create large dict (int keys)     130us    -80%
dict-create-1.5  Create large dict (string keys)  143us    -75%
   dict-set-1.1  Replace existing item            258ns    -34%
   dict-set-1.2  Replace nonexistent item         365ns    -49%
dict-exists-1.1  Find existing item              55.7ns     -5%
dict-exists-1.2  Find nonexistent item           55.0ns     -5%

Signed-off-by: default avatarSteve Bennett <steveb@workware.net.au>
      99b7ce97
  27. Jun 13, 2020
  29. Jun 12, 2020
  31. Jun 11, 2020
  33. Jun 10, 2020
  35. Jun 05, 2020