Add fast function to zero memory

2 files changed, 271 insertions, 10 deletions

diff --git a/source/tanya/memory/arch/x86_64.d b/source/tanya/memory/arch/x86_64.d
index 0c3b86f..2db1aaa 100644
--- a/source/tanya/memory/arch/x86_64.d
+++ b/source/tanya/memory/arch/x86_64.d
@@ -79,3 +79,192 @@ pure nothrow @system @nogc
         ret;
     }
 }
+
+pragma(inline, true)
+package (tanya.memory) void zero(void[] memory)
+pure nothrow @system @nogc
+{
+    asm pure nothrow @nogc
+    {
+        naked;
+    }
+    version (Windows) asm pure nothrow @nogc
+    {
+        /*
+         * RCX - array.
+         */
+        mov       R8,           [ RCX ];
+        mov       R9,           [ RCX + 8 ];
+    }
+    else asm pure nothrow @nogc
+    {
+        /*
+         * RSI - pointer.
+         * RDI - length.
+         */
+        mov       R8,           RDI;
+        mov       R9,           RSI;
+    }
+    asm pure nothrow @nogc
+    {
+        // Check for zero length.
+        test      R8,           R8;
+        jz        end;
+
+        // Set to 0.
+        pxor      XMM0,         XMM0;
+
+        // Check if the pointer is aligned to a 16-byte boundary.
+        and       R9,           -0x10;
+    }
+    // Compute the number of misaligned bytes.
+    version (Windows) asm pure nothrow @nogc
+    {
+        mov       RAX,          [ RCX + 8 ];
+    }
+    else asm pure nothrow @nogc
+    {
+        mov       RAX,          RSI;
+    }
+    asm pure nothrow @nogc
+    {
+        sub       RAX,          R9;
+
+        test      RAX,          RAX;
+        jz aligned;
+
+        // Get the number of bytes to be written until we are aligned.
+        mov       RDX,          0x10;
+        sub       RDX,          RAX;
+    }
+    version (Windows) asm pure nothrow @nogc
+    {
+        mov       R9,           [ RCX + 8 ];
+    }
+    else asm pure nothrow @nogc
+    {
+        mov       R9,           RSI;
+    }
+    asm pure nothrow @nogc
+    {
+        // Set RAX to zero, so we can set bytes and dwords.
+        xor       RAX,          RAX;
+
+    naligned:
+        mov       [ R9 ],       AL; // Write a byte.
+
+        // Advance the pointer. Decrease the total number of bytes
+        // and the misaligned ones.
+        inc       R9;
+        dec       RDX;
+        dec       R8;
+
+        // Checks if we are aligned.
+        test      RDX,          RDX;
+        jnz naligned;
+
+    aligned:
+        // Checks if we're done writing bytes.
+        test      R8,           R8;
+        jz end;
+
+        // Write 1 byte at a time.
+        cmp       R8,           8;
+        jl aligned_1;
+
+        // Write 8 bytes at a time.
+        cmp       R8,           16;
+        jl aligned_8;
+
+        // Write 16 bytes at a time.
+        cmp       R8,           32;
+        jl aligned_16;
+
+        // Write 32 bytes at a time.
+        cmp       R8,           64;
+        jl aligned_32;
+
+    aligned_64:
+        movdqa    [ R9 ],        XMM0;
+        movdqa    [ R9 + 16 ],   XMM0;
+        movdqa    [ R9 + 32 ],   XMM0;
+        movdqa    [ R9 + 48 ],   XMM0;
+
+        add       R9,            64;
+        sub       R8,            64;
+
+        cmp       R8,            64;
+        jge aligned_64;
+
+        // Checks if we're done writing bytes.
+        test      R8,            R8;
+        jz end;
+
+        // Write 1 byte at a time.
+        cmp       R8,            8;
+        jl aligned_1;
+
+        // Write 8 bytes at a time.
+        cmp       R8,            16;
+        jl aligned_8;
+
+        // Write 16 bytes at a time.
+        cmp       R8,            32;
+        jl aligned_16;
+
+    aligned_32:
+        movdqa    [ R9 ],        XMM0;
+        movdqa    [ R9 + 16 ],   XMM0;
+
+        add       R9,            32;
+        sub       R8,            32;
+
+        // Checks if we're done writing bytes.
+        test      R8,            R8;
+        jz end;
+
+        // Write 1 byte at a time.
+        cmp       R8,            8;
+        jl aligned_1;
+
+        // Write 8 bytes at a time.
+        cmp       R8,            16;
+        jl aligned_8;
+
+    aligned_16:
+        movdqa    [ R9 ],        XMM0;
+
+        add       R9,            16;
+        sub       R8,            16;
+
+        // Checks if we're done writing bytes.
+        test      R8,            R8;
+        jz end;
+
+        // Write 1 byte at a time.
+        cmp       R8,            8;
+        jl aligned_1;
+
+    aligned_8:
+        mov       [ R9 ],        RAX;
+
+        add       R9,            8;
+        sub       R8,            8;
+
+        // Checks if we're done writing bytes.
+        test      R8,            R8;
+        jz end;
+
+    aligned_1:
+        mov       [ R9 ],        AL;
+
+        inc       R9;
+        dec       R8;
+
+        test      R8,            R8;
+        jnz aligned_1;
+
+    end:
+        ret;
+    }
+}
diff --git a/source/tanya/memory/op.d b/source/tanya/memory/op.d
index 98e5b90..25f7d25 100644
--- a/source/tanya/memory/op.d
+++ b/source/tanya/memory/op.d
@@ -1,4 +1,4 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
+/* 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/. */
 
@@ -17,6 +17,8 @@ version (D_InlineAsm_X86_64)
     static import tanya.memory.arch.x86_64;
 }
 
+private enum alignmentMask = size_t.sizeof - 1;
+
 /**
  * Copies $(D_PARAM source) into $(D_PARAM target).
  *
@@ -24,7 +26,7 @@ version (D_InlineAsm_X86_64)
  * of $(D_PARAM target) points to an element of $(D_PARAM source).
  *
  * $(D_PARAM target) shall have enough space $(D_INLINECODE source.length)
- * elements. 
+ * elements.
  *
  * Params:
  *  source = Memory to copy from.
@@ -48,7 +50,6 @@ body
         auto source1 = cast(const(ubyte)*) source;
         auto target1 = cast(ubyte*) target;
         auto count = source.length;
-        enum alignmentMask = size_t.sizeof - 1;
 
         // Check if the pointers are aligned or at least can be aligned
         // properly.
@@ -79,19 +80,17 @@ body
         while (count--)
         {
             *target1++ = *source1++;
-        } 
+        }
     }
 }
 
 ///
 pure nothrow @safe @nogc unittest
 {
-    {
-        ubyte[9] source = [1, 2, 3, 4, 5, 6, 7, 8, 9];
-        ubyte[9] target;
-        source.copy(target);
-        assert(source == target);
-    }
+    ubyte[9] source = [1, 2, 3, 4, 5, 6, 7, 8, 9];
+    ubyte[9] target;
+    source.copy(target);
+    assert(source == target);
 }
 
 private pure nothrow @safe @nogc unittest
@@ -113,3 +112,76 @@ private pure nothrow @safe @nogc unittest
         assert(source == target);
     }
 }
+
+/**
+ * Fills $(D_PARAM memory) with zero-valued bytes.
+ *
+ * Param:
+ *  memory = Memory block.
+ */
+void zero(void[] memory) pure nothrow @trusted @nogc
+{
+    version (D_InlineAsm_X86_64)
+    {
+        tanya.memory.arch.x86_64.zero(memory);
+    }
+    else // Naive implementation.
+    {
+        auto n = memory.length;
+        ubyte* vp = cast(ubyte*) memory.ptr;
+
+        // Align.
+        while (((cast(size_t) vp) & alignmentMask) != 0)
+        {
+            *vp++ = 0;
+            --n;
+        }
+
+        // Set size_t.sizeof bytes at ones.
+        auto sp = cast(size_t*) vp;
+        while (n / size_t.sizeof > 0)
+        {
+            *sp++ = 0;
+            n -= size_t.sizeof;
+        }
+
+        // Write the remaining bytes.
+        vp = cast(ubyte*) sp;
+        while (n--)
+        {
+            *vp = 0;
+            ++vp;
+        }
+    }
+}
+
+///
+pure nothrow @safe @nogc unittest
+{
+    ubyte[9] memory = [1, 2, 3, 4, 5, 6, 7, 8, 9];
+    memory.zero();
+    foreach (ubyte v; memory)
+    {
+        assert(v == 0);
+    }
+}
+
+// Stress test. Checks that `zero` can handle unaligned pointers and different
+// lengths.
+pure nothrow @safe @nogc private unittest
+{
+    ubyte[192] memory;
+
+    foreach (j; 0 .. 192)
+    {
+        foreach (ubyte i, ref ubyte v; memory[j .. $])
+        {
+            v = i;
+        }
+        zero(memory[j .. $]);
+        foreach (ubyte v; memory[j .. $])
+        {
+            assert(v == 0);
+        }
+    }
+}