Initial Commit

common/embeddedaudiosynthesis/arm-wt-22k/lib_src/eas_flog.c

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+/*----------------------------------------------------------------------------
+ *
+ * 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;
+}
+