Small hash tables (eg those used in user class instances that only have a
few members) now only use the minimum amount of memory necessary to hold
the key/value pairs. This can reduce performance for instances that have
many members (because then there are many reallocations/rehashings of the
table), but helps to conserve memory.
See issue #1760.
Map indicies are most commonly a qstr, and adding a fast-path for hashing
of a qstr increases overall performance of the runtime.
On pyboard there is a 4% improvement in the pystone benchmark for a cost
of 20 bytes of code size. It's about a 2% improvement on unix.
This change makes the code behave how it was supposed to work when first
written. The avail_slot variable is set to the first free slot when
looking for a key (which would come from deleting an entry). So it's
more efficient (for subsequent lookups) to insert a new key into such a
slot, rather than the very last slot that was searched.
Hashing is now done using mp_unary_op function with MP_UNARY_OP_HASH as
the operator argument. Hashing for int, str and bytes still go via
fast-path in mp_unary_op since they are the most common objects which
need to be hashed.
This lead to quite a bit of code cleanup, and should be more efficient
if anything. It saves 176 bytes code space on Thumb2, and 360 bytes on
x86.
The only loss is that the error message "unhashable type" is now the
more generic "unsupported type for __hash__".
Given that there's already support for "fixed table" maps, which are
essentially ordered maps, the implementation of OrderedDict just extends
"fixed table" maps by adding an "is ordered" flag and add/remove
operations, and reuses 95% of objdict code, just making methods tolerant
to both dict and OrderedDict.
Some things are missing so far, like CPython-compatible repr and comparison.
OrderedDict is Disabled by default; enabled on unix and stmhal ports.
This patch makes MICROPY_PY_BUILTINS_SET compile-time option fully
disable the builtin set object (when set to 0). This includes removing
set constructor/comprehension from the grammar, the compiler and the
emitters. Now, enabling set costs 8168 bytes on unix x64, and 3576
bytes on stmhal.
Blanket wide to all .c and .h files. Some files originating from ST are
difficult to deal with (license wise) so it was left out of those.
Also merged modpyb.h, modos.h, modstm.h and modtime.h in stmhal/.
Two things: 1) set flags in copy properly; make mp_map_init() not be too
smart and do something with requested alloc size. Policy of using prime
numbers for alloc size is high-level policy which should be applied at
corresponding high levels. Low-level functions should just do what they're
asked to, because they don't have enough context to be smarter than that.
For example, munging with alloc size of course breaks dict copying (as
changing sizes requires rehashing).
When searching next time, such entry should be just skipped, not terminate
the search. It's known that marking techique is not efficient at the presense
of many removes, but namespace usage should not require many deletes, and
as for user dictionaries - well, open addressing map table with linear
rehashing and load factor of ~1 is not particularly efficient at all ;-).
TODO: May consider "shift other entries in cluster" approach as an
alternative.
Pretty much everyone needs to include map.h, since it's such an integral
part of the Micro Python object implementation. Thus, the definitions
are now in obj.h instead. map.h is removed.
A big change. Micro Python objects are allocated as individual structs
with the first element being a pointer to the type information (which
is itself an object). This scheme follows CPython. Much more flexible,
not necessarily slower, uses same heap memory, and can allocate objects
statically.
Also change name prefix, from py_ to mp_ (mp for Micro Python).
Damien George
Stephen Kyle
Paul Sokolovsky
xbe
John R. Lenton
ian-v