1 files changed, 96 insertions, 0 deletions
diff --git a/arm-wt-22k/lib_src/eas_flog.c b/arm-wt-22k/lib_src/eas_flog.c
new file mode 100644
index 0000000..647da2f
--- /dev/null
+++ b/arm-wt-22k/lib_src/eas_flog.c
@@ -0,0 +1,96 @@
+/*----------------------------------------------------------------------------
+ *
+ * File: 
+ * eas_flog2.c
+ *
+ * Contents and purpose:
+ * Fixed point square root
+ *
+ *
+ * Copyright (c) 2006 Sonic Network Inc.
+
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ *----------------------------------------------------------------------------
+ * Revision Control:
+ *   $Revision$
+ *   $Date$
+ *----------------------------------------------------------------------------
+*/
+
+#include "eas_types.h"
+#include "eas_math.h"
+
+#define MANTISSA_SHIFT			27
+#define MANTISSA_MASK			0x0000000f
+#define MANTISSA_LSB_SHIFT		7
+#define MANTISSA_LSB_MASK		0x000fffff
+#define LOG_EXPONENT_SHIFT		10
+#define INTERPOLATION_SHIFT		20
+#define MAX_NEGATIVE			(-2147483647-1)
+
+/* log lookup table */
+static const EAS_U16 eas_log2_table[] = 
+{
+	0, 90, 174, 254, 330, 402, 470, 536,
+	599, 659, 717, 773, 827, 879, 929, 977,
+	1024
+};
+
+/*----------------------------------------------------------------------------
+ * EAS_flog2()
+ *----------------------------------------------------------------------------
+ * Purpose: 
+ * Calculates the log2 of a 32-bit fixed point value
+ *
+ * Inputs:
+ * n = value of interest
+ *		
+ * Outputs:
+ * returns the log2 of n
+ *
+ *----------------------------------------------------------------------------
+*/
+EAS_I32 EAS_flog2 (EAS_U32 n)
+{
+	EAS_U32 exp;
+	EAS_U32 interp;
+
+	/* check for error condition */
+	if (n == 0)
+		return MAX_NEGATIVE;
+
+	/* find exponent */
+	for (exp = 31; exp > 0; exp--)
+	{
+		/* shift until we get a 1 bit in bit 31 */
+		if ((n & (EAS_U32) MAX_NEGATIVE) != 0)
+			break;
+		n <<= 1;
+	}
+	/*lint -e{701} use shift for performance */
+	exp <<= LOG_EXPONENT_SHIFT;
+
+	/* get the least significant bits for interpolation */
+	interp = (n >> MANTISSA_LSB_SHIFT) & MANTISSA_LSB_MASK;
+
+	/* get the most significant bits for mantissa lookup */
+	n = (n >> MANTISSA_SHIFT) & MANTISSA_MASK;
+
+	/* interpolate mantissa */
+	interp = ((eas_log2_table[n+1] - eas_log2_table[n]) * interp) >> INTERPOLATION_SHIFT;
+	exp += eas_log2_table[n] + interp;
+
+	return (EAS_I32) exp;
+}
+