gh-148675: Optimize arraydescr structure: use char[3]

[vstinner]

Replace "const char *typecode;" with "char typecode[3];" to make the arraydescr structure smaller and avoids an indirection.

• Issue: Add support for numpy buffer format Zf and Zd #148675

[read-the-docs-community]

Documentation build overview

📚 cpython-previews | 🛠️ Build #32562183 | 📁 Comparing 1b52f8c against main (70e365c)

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2 files changed

± library/functions.html
± whatsnew/3.15.html

[vstinner]

@scoder @encukou: Would you mind to review this change?

[scoder]

Looks good to me. Enough to change the struct field back to its previous (padded) size.

[scoder]

Personally, I would also have optimised the strcmp() calls into single character comparisons to make it clear to the C compiler that that's almost always enough for taking the decision, but that'd be an optimisation with yet-to-be-measured benefit, not a fix. Definitely not something that comes with a deadline.

[vstinner]

Thanks for merging my change @encukou :-)