1 files changed, 147 insertions, 0 deletions
diff --git a/js/src/ds/Sort.h b/js/src/ds/Sort.h
new file mode 100644
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef ds_Sort_h
+#define ds_Sort_h
+
+#include "jstypes.h"
+
+namespace js {
+
+namespace detail {
+
+template <typename T>
+MOZ_ALWAYS_INLINE void CopyNonEmptyArray(T* dst, const T* src, size_t nelems) {
+  MOZ_ASSERT(nelems != 0);
+  const T* end = src + nelems;
+  do {
+    *dst++ = *src++;
+  } while (src != end);
+}
+
+/* Helper function for MergeSort. */
+template <typename T, typename Comparator>
+MOZ_ALWAYS_INLINE bool MergeArrayRuns(T* dst, const T* src, size_t run1,
+                                      size_t run2, Comparator c) {
+  MOZ_ASSERT(run1 >= 1);
+  MOZ_ASSERT(run2 >= 1);
+
+  /* Copy runs already in sorted order. */
+  const T* b = src + run1;
+  bool lessOrEqual;
+  if (!c(b[-1], b[0], &lessOrEqual)) {
+    return false;
+  }
+
+  if (!lessOrEqual) {
+    /* Runs are not already sorted, merge them. */
+    for (const T* a = src;;) {
+      if (!c(*a, *b, &lessOrEqual)) {
+        return false;
+      }
+      if (lessOrEqual) {
+        *dst++ = *a++;
+        if (!--run1) {
+          src = b;
+          break;
+        }
+      } else {
+        *dst++ = *b++;
+        if (!--run2) {
+          src = a;
+          break;
+        }
+      }
+    }
+  }
+  CopyNonEmptyArray(dst, src, run1 + run2);
+  return true;
+}
+
+} /* namespace detail */
+
+/*
+ * Sort the array using the merge sort algorithm. The scratch should point to
+ * a temporary storage that can hold nelems elements.
+ *
+ * The comparator must provide the () operator with the following signature:
+ *
+ *     bool operator()(const T& a, const T& a, bool* lessOrEqualp);
+ *
+ * It should return true on success and set *lessOrEqualp to the result of
+ * a <= b operation. If it returns false, the sort terminates immediately with
+ * the false result. In this case the content of the array and scratch is
+ * arbitrary.
+ *
+ * Note: The merge sort algorithm is a stable sort, preserving relative ordering
+ * of entries that compare equal. This makes it a useful substitute for
+ * |std::stable_sort|, which can't be used in SpiderMonkey because it internally
+ * allocates memory without using SpiderMonkey's allocator.
+ */
+template <typename T, typename Comparator>
+[[nodiscard]] bool MergeSort(T* array, size_t nelems, T* scratch,
+                             Comparator c) {
+  const size_t INS_SORT_LIMIT = 3;
+
+  if (nelems <= 1) {
+    return true;
+  }
+
+  /*
+   * Apply insertion sort to small chunks to reduce the number of merge
+   * passes needed.
+   */
+  for (size_t lo = 0; lo < nelems; lo += INS_SORT_LIMIT) {
+    size_t hi = lo + INS_SORT_LIMIT;
+    if (hi >= nelems) {
+      hi = nelems;
+    }
+    for (size_t i = lo + 1; i != hi; i++) {
+      for (size_t j = i;;) {
+        bool lessOrEqual;
+        if (!c(array[j - 1], array[j], &lessOrEqual)) {
+          return false;
+        }
+        if (lessOrEqual) {
+          break;
+        }
+        T tmp = array[j - 1];
+        array[j - 1] = array[j];
+        array[j] = tmp;
+        if (--j == lo) {
+          break;
+        }
+      }
+    }
+  }
+
+  T* vec1 = array;
+  T* vec2 = scratch;
+  for (size_t run = INS_SORT_LIMIT; run < nelems; run *= 2) {
+    for (size_t lo = 0; lo < nelems; lo += 2 * run) {
+      size_t hi = lo + run;
+      if (hi >= nelems) {
+        detail::CopyNonEmptyArray(vec2 + lo, vec1 + lo, nelems - lo);
+        break;
+      }
+      size_t run2 = (run <= nelems - hi) ? run : nelems - hi;
+      if (!detail::MergeArrayRuns(vec2 + lo, vec1 + lo, run, run2, c)) {
+        return false;
+      }
+    }
+    T* swap = vec1;
+    vec1 = vec2;
+    vec2 = swap;
+  }
+  if (vec1 == scratch) {
+    detail::CopyNonEmptyArray(array, scratch, nelems);
+  }
+  return true;
+}
+
+} /* namespace js */
+
+#endif /* ds_Sort_h */