BAN: Expose radix sort with user provided buffer

This can be nice if user has memory for a the temporary buffer and
doesnt want the sorting to allocate or be able to fail.

Also counts are now stack allocated, there isn't really any reason to
allocate them on the heap as 256x 64 bit values only adds up to 2 KiB

BAN/include/BAN/Sort.h

@@ -137,27 +137,20 @@ namespace BAN::sort
 
 	template<typename It, size_t radix = 256>
 	requires is_unsigned_v<it_value_type_t<It>> && (radix > 0 && (radix & (radix - 1)) == 0)
-	BAN::ErrorOr<void> radix_sort(It begin, It end)
+	void radix_sort(It begin, It end, BAN::Span<it_value_type_t<It>> storage)
 	{
-		using value_type = it_value_type_t<It>;
-
 		const size_t len = distance(begin, end);
 		if (len <= 1)
-			return {};
+			return;
 
-		Vector<value_type> temp;
-		TRY(temp.resize(len));
-
-		Vector<size_t> counts;
-		TRY(counts.resize(radix));
+		ASSERT(storage.size() >= len);
 
 		constexpr size_t mask  = radix - 1;
 		constexpr size_t shift = detail::lsb_index(radix);
 
-		for (size_t s = 0; s < sizeof(value_type) * 8; s += shift)
+		for (size_t s = 0; s < sizeof(it_value_type_t<It>) * 8; s += shift)
 		{
-			for (auto& cnt : counts)
-				cnt = 0;
+			size_t counts[radix] {};
 			for (It it = begin; it != end; ++it)
 				counts[(*it >> s) & mask]++;
 
@@ -167,12 +160,27 @@ namespace BAN::sort
 			for (It it = end; it != begin;)
 			{
 				--it;
-				temp[--counts[(*it >> s) & mask]] = *it;
+				storage[--counts[(*it >> s) & mask]] = *it;
 			}
 
-			for (size_t j = 0; j < temp.size(); j++)
-				*next(begin, j) = temp[j];
+			It it = begin;
+			for (size_t j = 0; j < storage.size(); j++, ++it)
+				*it = storage[j];
 		}
+	}
+
+	template<typename It, size_t radix = 256>
+	requires is_unsigned_v<it_value_type_t<It>> && (radix > 0 && (radix & (radix - 1)) == 0)
+	BAN::ErrorOr<void> radix_sort(It begin, It end)
+	{
+		const size_t len = distance(begin, end);
+		if (len <= 1)
+			return {};
+
+		Vector<it_value_type_t<It>> temp;
+		TRY(temp.resize(len));
+
+		radix_sort(begin, end, temp.span());
 
 		return {};
 	}