[libc][stdlib] Implement heap sort. (#98582)

Author: lntue

libc/cmake/modules/LLVMLibCCompileOptionRules.cmake

@@ -49,10 +49,21 @@ function(_get_compile_options_from_flags output_var)
   set(${output_var} ${compile_options} PARENT_SCOPE)
 endfunction(_get_compile_options_from_flags)
 
+function(_get_compile_options_from_config output_var)
+  set(config_options "")
+
+  if(LIBC_CONF_QSORT_IMPL)
+    list(APPEND config_options "-DLIBC_QSORT_IMPL=${LIBC_CONF_QSORT_IMPL}")
+  endif()
+
+  set(${output_var} ${config_options} PARENT_SCOPE)
+endfunction(_get_compile_options_from_config)
+
 function(_get_common_compile_options output_var flags)
   _get_compile_options_from_flags(compile_flags ${flags})
+  _get_compile_options_from_config(config_flags)
 
-  set(compile_options ${LIBC_COMPILE_OPTIONS_DEFAULT} ${compile_flags})
+  set(compile_options ${LIBC_COMPILE_OPTIONS_DEFAULT} ${compile_flags} ${config_flags})
 
   if(LLVM_COMPILER_IS_GCC_COMPATIBLE)
     list(APPEND compile_options "-fpie")

libc/config/baremetal/config.json

@@ -22,5 +22,10 @@
     "LIBC_CONF_FREELIST_MALLOC_BUFFER_SIZE": {
       "value": 102400
     }
+  },
+  "qsort": {
+    "LIBC_CONF_QSORT_IMPL": {
+      "value": "LIBC_QSORT_HEAP_SORT"
+    }
   }
 }

libc/config/config.json

@@ -82,5 +82,11 @@
       "value": 0,
       "doc": "Configures optimizations for math functions. Values accepted are LIBC_MATH_SKIP_ACCURATE_PASS, LIBC_MATH_SMALL_TABLES, LIBC_MATH_NO_ERRNO, LIBC_MATH_NO_EXCEPT, and LIBC_MATH_FAST."
     }
+  },
+  "qsort": {
+    "LIBC_CONF_QSORT_IMPL": {
+      "value": "LIBC_QSORT_QUICK_SORT",
+      "doc": "Configures sorting algorithm for qsort and qsort_r. Values accepted are LIBC_QSORT_QUICK_SORT, LIBC_QSORT_HEAP_SORT."
+    }
   }
 }

libc/docs/configure.rst

@@ -44,6 +44,8 @@ to learn about the defaults for your platform and target.
     - ``LIBC_CONF_RAW_MUTEX_DEFAULT_SPIN_COUNT``: Default number of spins before blocking if a mutex is in contention (default to 100).
     - ``LIBC_CONF_RWLOCK_DEFAULT_SPIN_COUNT``: Default number of spins before blocking if a rwlock is in contention (default to 100).
     - ``LIBC_CONF_TIMEOUT_ENSURE_MONOTONICITY``: Automatically adjust timeout to CLOCK_MONOTONIC (default to true). POSIX API may require CLOCK_REALTIME, which can be unstable and leading to unexpected behavior. This option will convert the real-time timestamp to monotonic timestamp relative to the time of call.
+* **"qsort" options**
+    - ``LIBC_CONF_QSORT_IMPL``: Configures sorting algorithm for qsort and qsort_r. Values accepted are LIBC_QSORT_QUICK_SORT, LIBC_QSORT_HEAP_SORT.
 * **"scanf" options**
     - ``LIBC_CONF_SCANF_DISABLE_FLOAT``: Disable parsing floating point values in scanf and friends.
     - ``LIBC_CONF_SCANF_DISABLE_INDEX_MODE``: Disable index mode in the scanf format string.

libc/src/stdlib/CMakeLists.txt

@@ -258,9 +258,13 @@ add_entrypoint_object(
 add_header_library(
   qsort_util
   HDRS
+    qsort_data.h
     qsort_util.h
+    heap_sort.h
+    quick_sort.h
   DEPENDS
     libc.include.stdlib
+    libc.src.__support.CPP.cstddef
 )
 
 add_entrypoint_object(

libc/src/stdlib/heap_sort.h

@@ -0,0 +1,61 @@
+//===-- Implementation of heap sort -----------------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDLIB_HEAP_SORT_H
+#define LLVM_LIBC_SRC_STDLIB_HEAP_SORT_H
+
+#include "src/__support/CPP/cstddef.h"
+#include "src/stdlib/qsort_data.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace internal {
+
+// A simple in-place heapsort implementation.
+// Follow the implementation in https://en.wikipedia.org/wiki/Heapsort.
+
+LIBC_INLINE void heap_sort(const Array &array) {
+  size_t end = array.size();
+  size_t start = end / 2;
+
+  auto left_child = [](size_t i) -> size_t { return 2 * i + 1; };
+
+  while (end > 1) {
+    if (start > 0) {
+      // Select the next unheapified element to sift down.
+      --start;
+    } else {
+      // Extract the max element of the heap, moving a leaf to root to be sifted
+      // down.
+      --end;
+      array.swap(0, end);
+    }
+
+    // Sift start down the heap.
+    size_t root = start;
+    while (left_child(root) < end) {
+      size_t child = left_child(root);
+      // If there are two children, set child to the greater.
+      if (child + 1 < end &&
+          array.elem_compare(child, array.get(child + 1)) < 0)
+        ++child;
+
+      // If the root is less than the greater child
+      if (array.elem_compare(root, array.get(child)) >= 0)
+        break;
+
+      // Swap the root with the greater child and continue sifting down.
+      array.swap(root, child);
+      root = child;
+    }
+  }
+}
+
+} // namespace internal
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_STDLIB_HEAP_SORT_H

libc/src/stdlib/qsort.cpp

@@ -21,8 +21,11 @@ LLVM_LIBC_FUNCTION(void, qsort,
   if (array == nullptr || array_size == 0 || elem_size == 0)
     return;
   internal::Comparator c(compare);
-  internal::quicksort(internal::Array(reinterpret_cast<uint8_t *>(array),
-                                      array_size, elem_size, c));
+
+  auto arr = internal::Array(reinterpret_cast<uint8_t *>(array), array_size,
+                             elem_size, c);
+
+  internal::sort(arr);
 }
 
 } // namespace LIBC_NAMESPACE_DECL

libc/src/stdlib/qsort_data.h

@@ -0,0 +1,102 @@
+//===-- Data structures for sorting routines --------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDLIB_QSORT_DATA_H
+#define LLVM_LIBC_SRC_STDLIB_QSORT_DATA_H
+
+#include "src/__support/CPP/cstddef.h"
+#include "src/__support/macros/config.h"
+
+#include <stdint.h>
+
+namespace LIBC_NAMESPACE_DECL {
+namespace internal {
+
+using Compare = int(const void *, const void *);
+using CompareWithState = int(const void *, const void *, void *);
+
+enum class CompType { COMPARE, COMPARE_WITH_STATE };
+
+struct Comparator {
+  union {
+    Compare *comp_func;
+    CompareWithState *comp_func_r;
+  };
+  const CompType comp_type;
+
+  void *arg;
+
+  Comparator(Compare *func)
+      : comp_func(func), comp_type(CompType::COMPARE), arg(nullptr) {}
+
+  Comparator(CompareWithState *func, void *arg_val)
+      : comp_func_r(func), comp_type(CompType::COMPARE_WITH_STATE),
+        arg(arg_val) {}
+
+#if defined(__clang__)
+  // Recent upstream changes to -fsanitize=function find more instances of
+  // function type mismatches. One case is with the comparator passed to this
+  // class. Libraries will tend to pass comparators that take pointers to
+  // varying types while this comparator expects to accept const void pointers.
+  // Ideally those tools would pass a function that strictly accepts const
+  // void*s to avoid UB, or would use qsort_r to pass their own comparator.
+  [[clang::no_sanitize("function")]]
+#endif
+  int comp_vals(const void *a, const void *b) const {
+    if (comp_type == CompType::COMPARE) {
+      return comp_func(a, b);
+    } else {
+      return comp_func_r(a, b, arg);
+    }
+  }
+};
+
+class Array {
+  uint8_t *array;
+  size_t array_size;
+  size_t elem_size;
+  Comparator compare;
+
+public:
+  Array(uint8_t *a, size_t s, size_t e, Comparator c)
+      : array(a), array_size(s), elem_size(e), compare(c) {}
+
+  uint8_t *get(size_t i) const { return array + i * elem_size; }
+
+  void swap(size_t i, size_t j) const {
+    uint8_t *elem_i = get(i);
+    uint8_t *elem_j = get(j);
+    for (size_t b = 0; b < elem_size; ++b) {
+      uint8_t temp = elem_i[b];
+      elem_i[b] = elem_j[b];
+      elem_j[b] = temp;
+    }
+  }
+
+  int elem_compare(size_t i, const uint8_t *other) const {
+    // An element must compare equal to itself so we don't need to consult the
+    // user provided comparator.
+    if (get(i) == other)
+      return 0;
+    return compare.comp_vals(get(i), other);
+  }
+
+  size_t size() const { return array_size; }
+
+  // Make an Array starting at index |i| and size |s|.
+  Array make_array(size_t i, size_t s) const {
+    return Array(get(i), s, elem_size, compare);
+  }
+};
+
+using SortingRoutine = void(const Array &);
+
+} // namespace internal
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_STDLIB_QSORT_DATA_H

libc/src/stdlib/qsort_r.cpp

@@ -22,8 +22,10 @@ LLVM_LIBC_FUNCTION(void, qsort_r,
   if (array == nullptr || array_size == 0 || elem_size == 0)
     return;
   internal::Comparator c(compare, arg);
-  internal::quicksort(internal::Array(reinterpret_cast<uint8_t *>(array),
-                                      array_size, elem_size, c));
+  auto arr = internal::Array(reinterpret_cast<uint8_t *>(array), array_size,
+                             elem_size, c);
+
+  internal::sort(arr);
 }
 
 } // namespace LIBC_NAMESPACE_DECL