Preliminary 'log2()' and 'log2f()' implementation

The 'log2()' and 'log2f()' functions have been added in FreeBSD's libc
version 9.0.0, but they are missing in version 8.2.0, which is used in
Genode. This patch provides preliminary implementations of these
functions until the Genode libc gets updated to version 9.0.0 or above.

Fixes #143.

libports/lib/mk/gallium-aux.mk

@@ -19,9 +19,6 @@ SRC_C += u_format_access.c u_format_table.c
 # remove non-needed files from list
 SRC_C := $(filter-out u_indices.c u_unfilled_indices.c u_debug_memory.c,$(SRC_C))
 
-# definition of 'log2' that is missing in FreeBSD's libc
-CC_OPT_u_math = -D'log2(x)=(log(x)/log(2))'
-
 # dim build noise
 CC_OPT_draw_vertex           += -Wno-unused-but-set-variable
 CC_OPT_draw_vs_varient       += -Wno-enum-compare

libports/lib/mk/libm.mk

@@ -67,6 +67,9 @@ SRC_C  = $(wildcard $(LIBM_DIR)/src/*.c) \
          $(wildcard $(LIBM_DIR)/bsdsrc/*.c)
 SRC_C := $(filter-out $(FILTER_OUT),$(notdir $(SRC_C)))
 
+# remove on update to version 9
+SRC_C += log2.c
+
 #
 # 'e_rem_pio2.c' uses '__inline'
 #
@@ -76,4 +79,7 @@ vpath %.c $(LIBM_DIR)/src
 vpath %.c $(LIBM_DIR)/ld80
 vpath %.c $(LIBM_DIR)/bsdsrc
 
+# remove on update to version 9
+vpath log2.c $(REP_DIR)/src/lib/libc
+
 SHARED_LIB = yes

libports/src/lib/libc/log2.c

@@ -0,0 +1,26 @@
+/*
+ * \brief  Preliminary 'log2()' and 'log2f()' implementations
+ * \author Christian Prochaska
+ * \date   2012-03-06
+ */
+
+/*
+ * Copyright (C) 2008-2012 Genode Labs GmbH
+ *
+ * This file is part of the Genode OS framework, which is distributed
+ * under the terms of the GNU General Public License version 2.
+ */
+
+#include <math.h>
+
+
+double log2(double x)
+{
+	return log(x) / log(2);
+}
+
+
+float log2f(float x)
+{
+	return logf(x) / logf(2);
+}

libports/src/lib/libc/patches/log2.patch

@@ -0,0 +1,22 @@
+- add 'log2()' and 'log2f()' declarations
+- this patch is only needed for FreeBSD libc versions < 9
+
+diff --git a/msun/src/math.h b/msun/src/math.h
+--- msun/src/math.h
++++ msun/src/math.h
+@@ -204,6 +204,7 @@
+ double	ldexp(double, int);
+ double	log(double);
+ double	log10(double);
++double	log2(double);
+ double	modf(double, double *);	/* fundamentally !__pure2 */
+ 
+ double	pow(double, double);
+@@ -317,6 +318,7 @@
+ int	ilogbf(float) __pure2;
+ float	ldexpf(float, int);
+ float	log10f(float);
++float	log2f(float);
+ float	log1pf(float);
+ float	logf(float);
+ float	modff(float, float *);	/* fundamentally !__pure2 */