add missing file (bug #2843)

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@4254 65c4cc65-6c06-0410-ace0-fbb531ad65f3

codecs/log2comp.h

+/* log2comp.h - various base 2 log computation versions
+ * 
+ * Asterisk -- A telephony toolkit for Linux.
+ *
+ * Implementation by Alex Volkov <codepro@usa.net>
+ *
+ * Copyright (c) 2004, Digium
+ *
+ * This program is free software, distributed under the terms of
+ * the GNU General Public License
+ *
+ * Define WANT_ASM before including this file to use assembly
+ *   whenever possible
+ */
+
+#if defined(_MSC_VER)
+#	define inline __inline
+#elif defined(__GNUC__)
+#	define inline __inline__
+#else
+#	define inline
+#endif
+
+#if defined(WANT_ASM) && defined(_MSC_VER) && defined(_M_IX86)
+/* MS C Inline Asm */
+#	pragma warning( disable : 4035 )
+static inline int log2(int val) { __asm
+{
+	xor		eax, eax
+	dec		eax
+	bsr		eax, val
+}}
+#	pragma warning( default : 4035 )
+#elif defined(WANT_ASM) && defined(__GNUC__) && (defined(__i386__) || defined(i386))
+/* GNU Inline Asm */
+static inline int log2(int val)
+{
+	int a;
+	__asm__
+	("\
+		xorl	%0, %0		;\
+		decl	%0			;\
+		bsrl	%1, %0		;\
+		"
+		: "=r" (a)
+		: "mr" (val)
+		: "cc"
+	);
+	return a;
+}
+#else
+/* no ASM for this compiler and/or platform */
+/* rather slow base 2 log computation
+ * Using looped shift.
+ */
+static inline int log2(int val)
+{
+	int i;
+	for (i = -1; val; ++i, val >>= 1)
+		;
+	return (i);
+}
+#endif