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pythonGH-15558) The purpose of the `unicodedata.is_normalized` function is to answer the question `str == unicodedata.normalized(form, str)` more efficiently than writing just that, by using the "quick check" optimization described in the Unicode standard in UAX GH-15. However, it turns out the code doesn't implement the full algorithm from the standard, and as a result we often miss the optimization and end up having to compute the whole normalized string after all. Implement the standard's algorithm. This greatly speeds up `unicodedata.is_normalized` in many cases where our partial variant of quick-check had been returning MAYBE and the standard algorithm returns NO. At a quick test on my desktop, the existing code takes about 4.4 ms/MB (so 4.4 ns per byte) when the partial quick-check returns MAYBE and it has to do the slow normalize-and-compare: $ build.base/python -m timeit -s 'import unicodedata; s = "\uf900"*500000' \ -- 'unicodedata.is_normalized("NFD", s)' 50 loops, best of 5: 4.39 msec per loop With this patch, it gets the answer instantly (58 ns) on the same 1 MB string: $ build.dev/python -m timeit -s 'import unicodedata; s = "\uf900"*500000' \ -- 'unicodedata.is_normalized("NFD", s)' 5000000 loops, best of 5: 58.2 nsec per loop This restores a small optimization that the original version of this code had for the `unicodedata.normalize` use case. With this, that case is actually faster than in master! $ build.base/python -m timeit -s 'import unicodedata; s = "\u0338"*500000' \ -- 'unicodedata.normalize("NFD", s)' 500 loops, best of 5: 561 usec per loop $ build.dev/python -m timeit -s 'import unicodedata; s = "\u0338"*500000' \ -- 'unicodedata.normalize("NFD", s)' 500 loops, best of 5: 512 usec per loop (cherry picked from commit 2f09413) Co-authored-by: Greg Price <gnprice@gmail.com>
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