[libc-commits] [libc] [libc][wctype] Upstream custom slice implementation from PtrHash-cc prototype to LLVM libc (PR #174779)

[Marcell Leleszi via libc-commits]

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@@ -0,0 +1,117 @@
+//===-- Internal utils for wctype conversion code - slice -------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+// Similar to cpp::span with additional functionality
+
+#ifndef LLVM_LIBC_SRC___SUPPORT_WCTYPE_CONVERSION_UTILS_SLICE_H
+#define LLVM_LIBC_SRC___SUPPORT_WCTYPE_CONVERSION_UTILS_SLICE_H
+
+#include "hdr/types/size_t.h"
+#include "src/__support/CPP/algorithm.h"
+#include "src/__support/CPP/expected.h"
+#include "src/__support/CPP/span.h"
+#include "src/__support/libc_assert.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace wctype_internal {
+
+namespace conversion_utils {
+
+enum class Ordering {
+  /// An ordering where a compared value is less than another.
+  Less = -1,
+  /// An ordering where a compared value is equal to another.
+  Equal = 0,
+  /// An ordering where a compared value is greater than another.
+  Greater = 1,
+};
+
+template <typename T> struct Slice : public cpp::span<T> {
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mleleszi wrote:

In your code snippet you are working with a binary predicate: `this->part(h) < shard * parts_per_shard_ + part_in_shard`. It's just true/false with extra steps, you are not checking for equality,  you are searching for the first index your predicate becomes false if I understand correctly (where a partitions starts), which is exactly what `std::partition_point` is for.

https://github.com/llvm/llvm-project/pull/174779