Implement RtlCompareMemory is assembly, not used yet.

svn path=/branches/ros-amd64-bringup/; revision=37473

reactos/lib/rtl/amd64/rtlmem.S

@@ -0,0 +1,78 @@
+/*
+ * COPYRIGHT:         See COPYING in the top level directory
+ * PROJECT:           ReactOS Run-Time Library
+ * PURPOSE:           Memory functions for amd64
+ * FILE:              lib/rtl/i386/rtlswap.S
+ * PROGRAMER:         Timo Kreuzer (timo.kreuzer@reactos.org)
+ */
+
+/* INCLUDES ******************************************************************/
+
+#include <ndk/amd64/asmmacro.S>
+
+/* FUNCTIONS *****************************************************************/
+.intel_syntax noprefix
+
+/* SIZE_T 
+ * RtlCompareMemory(
+ *   IN CONST VOID *Source1, <rcx>
+ *   IN CONST VOID *Source2, <rdx>
+ *   IN SIZE_T  Length <r8>
+ * );
+ */
+.proc RtlCompareMemory
+
+    /* Save registers */
+    push rsi
+    .pushreg rsi
+    push rdi
+    .pushreg rdi
+
+    /* Setup registers for compare */
+    mov rsi, rcx
+    mov rdi, rdx
+
+    /* Clear direction flag */
+    cli
+
+    /* Get number of qwords */
+    mov rcx, r8
+    shr rcx, 3
+    jz 2f
+
+    /* Compare qwords */
+    repe cmpsq
+    jnz 4f
+
+2:  /* Compare rest */
+    mov rcx, r8
+    and rcx, 7
+    jz 3f
+
+    repe cmpsb
+    jnz 5f
+
+3:  /* All equal */
+    /* Return the full count */
+    mov rax, rcx
+    jmp 6f
+
+4:  /* Not equal after comparing qwords */
+    /* Compare the last qword */
+    sub rsi, 8
+    sub rdi, 8
+    mov rcx, 8
+    repe cmpsb
+
+5:  /* Not equal after comparing bytes */
+    /* Return difference */
+    sub rdi, rdx
+    dec rdi
+    mov rax, rdi
+
+6:  /* Cleanup and return */
+    pop rdi
+    pop rsi
+    ret
+.endproc
+