Fix radix_sort_by_key for desc order #593
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Radix sort algorithm was not stable when used for sorting by key in descending order (see issue boostorg#588).
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looks good 👍 |
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This should fix #588.
Now in radix sort when
greater<T>()is specified as comparison function (desc order) instead of performing asc-ordered radix sort and then reversing the result, descending radix sort is performed.It's done by negating input value if its type is a signed type and by subtracting the input value from the maximum value of value's type in other cases (in
radix()function). That way values seem "reversed" and we get desc order. It should also be faster than sorting in asc order and then reversing the result.I also added some test for desc-ordered radix sort and radix sort by key.