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

Thu Jul 11 19:42:25 PDT 2024

llvmbot wrote:




@llvm/pr-subscribers-libc

Author: None (lntue)

<details>
<summary>Changes</summary>



---
Full diff: https://github.com/llvm/llvm-project/pull/98582.diff


9 Files Affected:

- (modified) libc/cmake/modules/LLVMLibCCompileOptionRules.cmake (+12-1) 
- (modified) libc/config/baremetal/config.json (+5) 
- (modified) libc/config/config.json (+6) 
- (modified) libc/docs/configure.rst (+2) 
- (modified) libc/src/stdlib/CMakeLists.txt (+2) 
- (added) libc/src/stdlib/heap_sort.h (+54) 
- (modified) libc/src/stdlib/qsort.cpp (+10-2) 
- (modified) libc/src/stdlib/qsort_r.cpp (+8-2) 
- (modified) libc/src/stdlib/qsort_util.h (+15-4) 


``````````diff

diff --git a/libc/cmake/modules/LLVMLibCCompileOptionRules.cmake b/libc/cmake/modules/LLVMLibCCompileOptionRules.cmake
index c5e7dfe8abd0f..097d9cb2fd1b9 100644
--- a/libc/cmake/modules/LLVMLibCCompileOptionRules.cmake
+++ b/libc/cmake/modules/LLVMLibCCompileOptionRules.cmake
@@ -34,10 +34,21 @@ 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")
diff --git a/libc/config/baremetal/config.json b/libc/config/baremetal/config.json
index dda4c42425755..f2bc6e6517f7c 100644
--- a/libc/config/baremetal/config.json
+++ b/libc/config/baremetal/config.json
@@ -17,5 +17,10 @@
     "LIBC_CONF_FREELIST_MALLOC_BUFFER_SIZE": {
       "value": 102400
     }
+  },
+  "qsort": {
+    "LIBC_CONF_QSORT_IMPL": {
+      "value": "LIBC_QSORT_HEAP_SORT"
+    }
   }
 }
diff --git a/libc/config/config.json b/libc/config/config.json
index e8feab20175f4..e6a65d6689ec7 100644
--- a/libc/config/config.json
+++ b/libc/config/config.json
@@ -76,5 +76,11 @@
       "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."
+    }
   }
 }
diff --git a/libc/docs/configure.rst b/libc/docs/configure.rst
index 9c641ef94570f..777330d815756 100644
--- a/libc/docs/configure.rst
+++ b/libc/docs/configure.rst
@@ -42,6 +42,8 @@ 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.
diff --git a/libc/src/stdlib/CMakeLists.txt b/libc/src/stdlib/CMakeLists.txt
index 7b7e55db391fa..e19d97b1025d9 100644
--- a/libc/src/stdlib/CMakeLists.txt
+++ b/libc/src/stdlib/CMakeLists.txt
@@ -259,8 +259,10 @@ add_header_library(
   qsort_util
   HDRS
     qsort_util.h
+    heap_sort.h
   DEPENDS
     libc.include.stdlib
+    libc.src.__support.CPP.cstddef
 )
 
 add_entrypoint_object(
diff --git a/libc/src/stdlib/heap_sort.h b/libc/src/stdlib/heap_sort.h
new file mode 100644
index 0000000000000..63aba88fb933f
--- /dev/null
+++ b/libc/src/stdlib/heap_sort.h
@@ -0,0 +1,54 @@
+//===-- 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 "qsort_util.h"
+#include "src/__support/CPP/cstddef.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) {
+      --start;
+    } else {
+      --end;
+      array.swap(0, end);
+    }
+
+    size_t root = start;
+    while (left_child(root) < end) {
+      size_t child = left_child(root);
+      if (child + 1 < end &&
+          array.elem_compare(child, array.get(child + 1)) < 0)
+        ++child;
+
+      if (array.elem_compare(root, array.get(child)) >= 0)
+        break;
+
+      array.swap(root, child);
+      root = child;
+    }
+  }
+}
+
+} // namespace internal
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_STDLIB_HEAP_SORT_H
diff --git a/libc/src/stdlib/qsort.cpp b/libc/src/stdlib/qsort.cpp
index 048e63ab214ed..fb6bfa006eb1f 100644
--- a/libc/src/stdlib/qsort.cpp
+++ b/libc/src/stdlib/qsort.cpp
@@ -9,6 +9,7 @@
 #include "src/stdlib/qsort.h"
 #include "src/__support/common.h"
 #include "src/__support/macros/config.h"
+#include "src/stdlib/heap_sort.h"
 #include "src/stdlib/qsort_util.h"
 
 #include <stdint.h>
@@ -21,8 +22,15 @@ 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);
+
+#if LIBC_QSORT_IMPL == LIBC_QSORT_QUICK_SORT
+  internal::quick_sort(arr);
+#elif LIBC_QSORT_IMPL == LIBC_QSORT_HEAP_SORT
+  internal::heap_sort(arr);
+#endif
 }
 
 } // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/stdlib/qsort_r.cpp b/libc/src/stdlib/qsort_r.cpp
index efbe5ad484b0e..3c9bb5aa21f43 100644
--- a/libc/src/stdlib/qsort_r.cpp
+++ b/libc/src/stdlib/qsort_r.cpp
@@ -22,8 +22,14 @@ 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);
+
+#if LIBC_QSORT_IMPL == LIBC_QSORT_QUICK_SORT
+  internal::quick_sort(arr);
+#elif LIBC_QSORT_IMPL == LIBC_QSORT_HEAP_SORT
+  internal::heap_sort(arr);
+#endif
 }
 
 } // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/stdlib/qsort_util.h b/libc/src/stdlib/qsort_util.h
index 3a9cc4b8669f8..87945c26b3c93 100644
--- a/libc/src/stdlib/qsort_util.h
+++ b/libc/src/stdlib/qsort_util.h
@@ -12,7 +12,18 @@
 #include "src/__support/macros/attributes.h"
 #include "src/__support/macros/config.h"
 #include <stdint.h>
-#include <stdlib.h>
+
+#define LIBC_QSORT_QUICK_SORT 1
+#define LIBC_QSORT_HEAP_SORT 2
+
+#ifndef LIBC_QSORT_IMPL
+#define LIBC_QSORT_IMPL LIBC_QSORT_QUICK_SORT
+#endif // LIBC_QSORT_IMPL
+
+#if (LIBC_QSORT_IMPL != LIBC_QSORT_QUICK_SORT &&                               \
+     LIBC_QSORT_IMPL != LIBC_QSORT_HEAP_SORT)
+#error "LIBC_QSORT_IMPL is not recognized."
+#endif
 
 namespace LIBC_NAMESPACE_DECL {
 namespace internal {
@@ -136,7 +147,7 @@ static size_t partition(const Array &array) {
   }
 }
 
-LIBC_INLINE void quicksort(const Array &array) {
+LIBC_INLINE void quick_sort(const Array &array) {
   const size_t array_size = array.size();
   if (array_size <= 1)
     return;
@@ -145,8 +156,8 @@ LIBC_INLINE void quicksort(const Array &array) {
     // The partition operation sorts the two element array.
     return;
   }
-  quicksort(array.make_array(0, split_index));
-  quicksort(array.make_array(split_index, array.size() - split_index));
+  quick_sort(array.make_array(0, split_index));
+  quick_sort(array.make_array(split_index, array.size() - split_index));
 }
 
 } // namespace internal

``````````

</details>


https://github.com/llvm/llvm-project/pull/98582
