milesgranger commented on code in PR #14696:
URL: https://github.com/apache/arrow/pull/14696#discussion_r1035902151
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cpp/src/arrow/compute/kernels/scalar_nested.cc:
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@@ -96,6 +97,22 @@ std::string ToString(const std::optional<T>& o) {
return o.has_value() ? ToChars(*o) : "(nullopt)";
}
+int64_t MaxSliceLength(const int64_t start, const int64_t stop, const int64_t
step) {
+ const auto startf = static_cast<float>(start);
+ const auto stopf = static_cast<float>(stop);
+ const auto stepf = static_cast<float>(step);
+
+ if (stopf - startf <= stepf) {
+ return 1;
+ }
+
+ auto length = static_cast<int64_t>(std::floor((stopf - startf) / stepf));
+ if (fmod(static_cast<float>(length), stepf) > 0.0) {
+ ++length;
+ }
+ return length;
Review Comment:
More tests added, let me know if you see any specific combinations you'd
like to see.
> (also, shouldn't it be fmod(stop-start, step) instead?)
It needs to be `length`, which if there is no step (rather when step==1),
then `stop-start` is okay, but that divided by step gives the actual length if
step != 1. Then if there is any remainder one more is added to the possible
length.
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