pitrou commented on a change in pull request #11298:
URL: https://github.com/apache/arrow/pull/11298#discussion_r721353442
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File path: cpp/src/arrow/compute/kernels/scalar_string.cc
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@@ -592,6 +592,70 @@ struct Utf8ReverseTransform : public StringTransformBase {
template <typename Type>
using Utf8Reverse = StringTransformExec<Type, Utf8ReverseTransform>;
+struct Utf8NfTransformBase : public StringTransformBase {
+ int64_t MaxCodeunits(int64_t ninputs, int64_t input_ncodeunits) override {
+ // Section 5.18 of the Unicode spec claims that the number of codepoints
for case
Review comment:
Answer: there are really pathological cases, so I think it would be
better to dynamically resize the output:
```python
>>> s = "\ufdfa"
>>> len(s)
1
>>> len(unicodedata.normalize("NFKD", s))
18
>>> len(unicodedata.normalize("NFD", s))
1
>>> len(unicodedata.normalize("NFKC", s))
18
>>> len(unicodedata.normalize("NFC", s))
1
```
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