Add memory.op.copyBackward

Added function that can copy memory chunks that can overlap.

source/tanya/memory/arch/x86_64.d

@@ -82,6 +82,8 @@ pure nothrow @system @nogc
     }
 }
 
+package (tanya.memory) template fill(ubyte Byte)
+{
     private enum const(char[]) MovArrayPointer(string Destination)()
     {
         string asmCode = "asm pure nothrow @nogc { mov ";
@@ -97,8 +99,7 @@ private enum const(char[]) MovArrayPointer(string Destination)()
     }
 
     pragma(inline, true)
-package (tanya.memory) void fill(ubyte Byte)(void[] memory)
+    void fill(void[] memory)
-pure nothrow @system @nogc
     {
         asm pure nothrow @nogc
         {
@@ -285,3 +286,57 @@ pure nothrow @system @nogc
             ret;
         }
     }
+}
+
+pragma(inline, true)
+package (tanya.memory) void copyBackward(const void[] source, void[] target)
+pure nothrow @system  @nogc
+{
+    asm pure nothrow @nogc
+    {
+        naked;
+
+        // Save the registers should be restored.
+        mov R8, RSI;
+        mov R9, RDI;
+    }
+    // Prepare the registers for movsb.
+    version (Windows) asm pure nothrow @nogc
+    {
+        // RDX - source.
+        // RCX - target.
+
+        mov RAX, [ RCX + 8 ];
+        mov R10, [ RDX + 8 ];
+        mov RCX, [ RDX ];
+
+        lea RDI, [ RAX + RCX - 1 ];
+        lea RSI, [ R10 + RCX - 1 ];
+    }
+    else asm pure nothrow @nogc
+    {
+        // RDX - source length.
+        // RCX - source data.
+        // RDI - target length
+        // RSI - target data.
+
+        lea RDI, [ RSI + RDX - 1 ];
+        lea RSI, [ RCX + RDX - 1 ];
+        mov RCX, RDX;
+    }
+    asm pure nothrow @nogc
+    {
+        std; // Set the direction flag.
+
+        rep;
+        movsb;
+
+        cld; // Clear the direction flag.
+
+        // Restore registers.
+        mov RDI, R9;
+        mov RSI, R8;
+
+        ret;
+    }
+}

source/tanya/memory/op.d

@@ -17,21 +17,23 @@ version (D_InlineAsm_X86_64)
     static import tanya.memory.arch.x86_64;
 }
 
-private enum alignmentMask = size_t.sizeof - 1;
+private enum alignMask = size_t.sizeof - 1;
 
 /**
  * Copies $(D_PARAM source) into $(D_PARAM target).
  *
- * $(D_PARAM source) and $(D_PARAM target) shall not overlap so that an element
+ * $(D_PARAM source) and $(D_PARAM target) shall not overlap so that
- * of $(D_PARAM target) points to an element of $(D_PARAM source).
+ * $(D_PARAM source) points ahead of $(D_PARAM target).
  *
- * $(D_PARAM target) shall have enough space $(D_INLINECODE source.length)
+ * $(D_PARAM target) shall have enough space for $(D_INLINECODE source.length)
  * elements.
  *
  * Params:
  *  source = Memory to copy from.
  *  target = Destination memory.
  *
+ * See_Also: $(D_PSYMBOL copyBackward).
+ *
  * Precondition: $(D_INLINECODE source.length <= target.length).
  */
 void copy(const void[] source, void[] target) pure nothrow @trusted @nogc
@@ -53,8 +55,8 @@ body
 
         // Check if the pointers are aligned or at least can be aligned
         // properly.
-        ushort naligned = (cast(size_t) source.ptr) & alignmentMask;
+        ushort naligned = (cast(size_t) source.ptr) & alignMask;
-        if (naligned == ((cast(size_t) target.ptr) & alignmentMask))
+        if (naligned == ((cast(size_t) target.ptr) & alignMask))
         {
             // Align the pointers if possible.
             if (naligned != 0)
@@ -135,7 +137,7 @@ package template FilledBytes(ubyte Byte, ubyte I = 0)
  *  Byte   = The value to fill $(D_PARAM memory) with.
  *  memory = Memory block.
  */
-void fill(ubyte Byte = 0)(void[] memory) pure nothrow @trusted @nogc
+void fill(ubyte Byte = 0)(void[] memory) @trusted
 {
     version (D_InlineAsm_X86_64)
     {
@@ -147,7 +149,7 @@ void fill(ubyte Byte = 0)(void[] memory) pure nothrow @trusted @nogc
         ubyte* vp = cast(ubyte*) memory.ptr;
 
         // Align.
-        while (((cast(size_t) vp) & alignmentMask) != 0)
+        while (((cast(size_t) vp) & alignMask) != 0)
         {
             *vp++ = Byte;
             --n;
@@ -206,3 +208,80 @@ pure nothrow @safe @nogc private unittest
         }
     }
 }
+
+/**
+ * Copies starting from the end of $(D_PARAM source) into the end of
+ * $(D_PARAM target).
+ *
+ * $(D_PSYMBOL copyBackward) copies the elements in reverse order, but the
+ * order of elements in the $(D_PARAM target) is exactly the same as in the
+ * $(D_PARAM source).
+ *
+ * $(D_PARAM source) and $(D_PARAM target) shall not overlap so that
+ * $(D_PARAM target) points ahead of $(D_PARAM source).
+ *
+ * $(D_PARAM target) shall have enough space for $(D_INLINECODE source.length)
+ * elements.
+ *
+ * Params:
+ *  source = Memory to copy from.
+ *  target = Destination memory.
+ *
+ * See_Also: $(D_PSYMBOL copy).
+ *
+ * Precondition: $(D_INLINECODE source.length <= target.length).
+ */
+void copyBackward(const void[] source, void[] target) pure nothrow @trusted @nogc
+in
+{
+    assert(source.length <= target.length);
+}
+body
+{
+    version (D_InlineAsm_X86_64)
+    {
+        tanya.memory.arch.x86_64.copyBackward(source, target);
+    }
+    else // Naive implementation.
+    {
+        auto count = source.length;
+
+        // Try to align the pointers if possible.
+        if (((cast(size_t) source.ptr) & alignMask) == ((cast(size_t) target.ptr) & alignMask))
+        {
+            while (((cast(size_t) (source.ptr + count)) & alignMask) != 0)
+            {
+                if (!count--)
+                {
+                    return;
+                }
+                (cast(ubyte[]) target)[count]
+                    = (cast(const(ubyte)[]) source)[count];
+            }
+        }
+
+        // Write as long we're aligned.
+        for (; count >= size_t.sizeof; count -= size_t.sizeof)
+        {
+                *(cast(size_t*) (target.ptr + count - size_t.sizeof))
+                    = *(cast(const(size_t)*) (source.ptr + count - size_t.sizeof));
+        }
+
+        // Write the remaining bytes.
+        while (count--)
+        {
+            (cast(ubyte[]) target)[count]
+                = (cast(const(ubyte)[]) source)[count];
+        }
+    }
+}
+
+///
+pure nothrow @safe @nogc unittest
+{
+    ubyte[6] mem = [ 'a', 'a', 'b', 'b', 'c', 'c' ];
+    ubyte[6] expected = [ 'a', 'a', 'a', 'a', 'b', 'b' ];
+
+    copyBackward(mem[0 .. 4], mem[2 .. $]);
+    assert(expected == mem);
+}