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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Avoid temporary allocation in dec_as_long()","articleBody":"# Feature or enhancement\n\n### Proposal:\n\nAfter #127925, new code in the decimal module (using the [PEP 757](https://peps.python.org/pep-0757/)) do temporary allocation with mpdecimal's memory functions (in mpd_qexport_u32/16()), just as before:\nhttps://github.com/python/cpython/blob/f10b7b29cb2a3cb67d1da114ef9a27be7e62dddd/Modules/_decimal/_decimal.c#L3691-L3706\n\nAccording to [the documentation](https://www.bytereef.org/mpdecimal/doc/libmpdec/various.html#exporting), we can prepare array of digits, which size could be estimated by mpd_sizeinbase().  Given this, the mpd_qexport_u32/16() shouldn't do any resize for this array.  [Here is Stefan comment](https://github.com/python/cpython/pull/127925#issuecomment-2560458812) on how safe this approach is:\n\u003e mpd_sizeinbase() uses log10() from math.h for performance reasons. If log10() is IEEE compliant, the result should be sufficiently large. Resizing is for guarding against broken log10() implementations.\n\u003e\n\u003e The current code in _decimal.c sets the libmpdec allocation functions to PyMem_Malloc() etc. So if longobject uses PyMem_Free() it is safe even when resizing occurs.\n\u003e\n\u003e If the new API allows for allocators other that PyMem_Malloc(), it will rely on the IEEE compliance of log10().\n\u003e\n\u003e    Stefan Krah\n\nWe can expect slight performance boost for small (2-3 digits) integers.\n\nThe thread on mpdecimal-discuss maillist:\nhttps://lists.sr.ht/~mpdecimal/mpdecimal-discuss/%3CZ2kIike42Wl0_YKd@skirpichev.msk.ru%3E\n\n\n### Has this already been discussed elsewhere?\n\nThis is a minor feature, which does not need previous discussion elsewhere\n\n### Links to previous discussion of this feature:\n\n_No response_\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-129630\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/skirpichev","@type":"Person","name":"skirpichev"},"datePublished":"2025-01-25T02:50:31.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":8},"url":"https://github.com/129275/cpython/issues/129275"}