1 files changed, 137 insertions, 0 deletions
diff --git a/js/src/ds/Sort.h b/js/src/ds/Sort.h
new file mode 100644
index 000000000..e5870a350
--- /dev/null
+++ b/js/src/ds/Sort.h
@@ -0,0 +1,137 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * 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.
+ */
+template<typename T, typename Comparator>
+MOZ_MUST_USE 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 */