From c5eb2f27be3a524f9c6e7de356e286146d00ed49 Mon Sep 17 00:00:00 2001
From: Eugen Wissner <belka@caraus.de>
Date: Fri, 28 Sep 2018 05:40:33 +0200
Subject: [PATCH] Add algorithm.iteration

---
 source/tanya/algorithm/iteration.d | 169 +++++++++++++++++++++++++++++
 source/tanya/math/mp.d             |  16 ++-
 2 files changed, 176 insertions(+), 9 deletions(-)

diff --git a/source/tanya/algorithm/iteration.d b/source/tanya/algorithm/iteration.d
index 9d0a4a8..27fce71 100644
--- a/source/tanya/algorithm/iteration.d
+++ b/source/tanya/algorithm/iteration.d
@@ -407,3 +407,172 @@ if (isInputRange!R)
         assert(slice.back == 3);
     }
 }
+
+/**
+ * Iterates a bidirectional range backwards.
+ *
+ * If $(D_PARAM Range) is a random-access range as well, the resulting range
+ * is a random-access range too.
+ *
+ * Params:
+ *  Range = Bidirectional range type.
+ *  range = Bidirectional range.
+ *
+ * Returns: Bidirectional range with the elements order reversed.
+ */
+auto retro(Range)(Range range)
+if (isBidirectionalRange!Range)
+{
+    static struct Retro
+    {
+        Range source;
+
+        @disable this();
+
+        private this(Range source)
+        {
+            this.source = source;
+        }
+
+        Retro save()
+        {
+            return this;
+        }
+
+        @property auto ref front()
+        in (!empty)
+        {
+            return this.source.back;
+        }
+
+        void popFront()
+        in (!empty)
+        {
+            this.source.popBack();
+        }
+
+        @property auto ref back()
+        in (!empty)
+        {
+            return this.source.front;
+        }
+
+        void popBack()
+        in (!empty)
+        {
+            this.source.popFront();
+        }
+
+        @property bool empty()
+        {
+            return this.source.empty;
+        }
+
+        static if (hasLength!Range)
+        {
+            @property size_t length()
+            {
+                return this.source.length;
+            }
+        }
+
+        static if (isRandomAccessRange!Range && hasLength!Range)
+        {
+            auto ref opIndex(size_t i)
+            in (i < length)
+            {
+                return this.source[$ - ++i];
+            }
+        }
+
+        static if (hasAssignableElements!Range)
+        {
+            @property void front(ref ElementType!Range value)
+            in (!empty)
+            {
+                this.source.back = value;
+            }
+
+            @property void front(ElementType!Range value)
+            in (!empty)
+            {
+                this.source.back = move(value);
+            }
+
+            @property void back(ref ElementType!Range value)
+            in (!empty)
+            {
+                this.source.front = value;
+            }
+
+            @property void back(ElementType!Range value)
+            in (!empty)
+            {
+                this.source.front = move(value);
+            }
+
+            static if (isRandomAccessRange!Range && hasLength!Range)
+            {
+                void opIndexAssign(ref ElementType!Range value, size_t i)
+                in (i < length)
+                {
+                    this.source[$ - ++i] = value;
+                }
+
+                void opIndexAssign(ElementType!Range value, size_t i)
+                in (i < length)
+                {
+                    this.source[$ - ++i] = move(value);
+                }
+            }
+        }
+    }
+
+    return Retro(range);
+}
+
+///
+@nogc nothrow pure @safe unittest
+{
+    import tanya.algorithm.comparison : equal;
+
+    const int[3] given = [1, 2, 3];
+    const int[3] expected = [3, 2, 1];
+
+    auto actual = retro(given[]);
+
+    assert(actual.length == expected.length);
+    assert(!actual.empty);
+    assert(equal(actual, expected[]));
+}
+
+// Elements are accessible in reverse order
+@nogc nothrow pure @safe unittest
+{
+    const int[3] given = [1, 2, 3];
+    auto actual = retro(given[]);
+
+    assert(actual.back == given[].front);
+    assert(actual[0] == 3);
+    assert(actual[2] == 1);
+
+    actual.popBack();
+    assert(actual.back == 2);
+    assert(actual[1] == 2);
+}
+
+// Elements can be assigned
+@nogc nothrow pure @safe unittest
+{
+    int[4] given = [1, 2, 3, 4];
+    auto actual = retro(given[]);
+
+    actual.front = 5;
+    assert(given[].back == 5);
+
+    actual.back = 8;
+    assert(given[].front == 8);
+
+    actual[2] = 10;
+    assert(given[1] == 10);
+}
diff --git a/source/tanya/math/mp.d b/source/tanya/math/mp.d
index ed47c1e..5ee1f39 100644
--- a/source/tanya/math/mp.d
+++ b/source/tanya/math/mp.d
@@ -14,15 +14,16 @@
  */
 module tanya.math.mp;
 
-import std.algorithm.mutation : fill, reverse;
-import std.range;
+import std.algorithm.mutation : fill;
 import tanya.algorithm.comparison;
+import tanya.algorithm.iteration;
 import tanya.algorithm.mutation;
 import tanya.container.array;
 import tanya.encoding.ascii;
 import tanya.memory;
 import tanya.meta.trait;
 import tanya.meta.transform;
+import tanya.range;
 
 /**
  * Algebraic sign.
@@ -929,7 +930,7 @@ struct Integer
             const shift = digitBitCount - bit;
             digit carry;
 
-            foreach (ref d; this.rep[0 .. this.size].retro)
+            foreach_reverse (ref d; this.rep[0 .. this.size])
             {
                 const newCarry = d & mask;
                 d = (d >> bit) | (carry << shift);
@@ -1505,14 +1506,11 @@ struct Integer
             tmp = this;
         }
 
-        do
+        array.length = length;
+        for (size_t i = array.length - 1; tmp != 0; tmp >>= 8, --i)
         {
-            array.insertBack(cast(ubyte) (tmp.rep[0] & 0xff));
-            tmp >>= 8;
+            array[i] = (cast(ubyte) (tmp.rep[0] & 0xff));
         }
-        while (tmp != 0);
-
-        array[].reverse();
 
         return array;
     }