1 files changed, 168 insertions, 0 deletions
diff --git a/arm-fm-22k/lib_src/eas_math.c b/arm-fm-22k/lib_src/eas_math.c
new file mode 100644
index 0000000..12d788e
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+++ b/arm-fm-22k/lib_src/eas_math.c
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+/*----------------------------------------------------------------------------
+ *
+ * File: 
+ * eas_math.c
+ *
+ * Contents and purpose:
+ * Contains common math routines for the various audio engines.
+ *
+ *
+ * Copyright Sonic Network Inc. 2005
+
+ * 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: 586 $
+ *   $Date: 2007-03-08 20:33:04 -0800 (Thu, 08 Mar 2007) $
+ *----------------------------------------------------------------------------
+*/
+
+#include "eas.h"
+#include "eas_math.h"
+
+/* anything less than this converts to a fraction too small to represent in 32-bits */
+#define MIN_CENTS	-18000
+
+/*----------------------------------------------------------------------------
+ * EAS_Calculate2toX()
+ *----------------------------------------------------------------------------
+ * Purpose:
+ * Calculate 2^x
+ *
+ * Inputs:
+ * nCents - 	measured in cents
+ * psEASData - pointer to overall EAS data structure
+ *
+ * Outputs:
+ * nResult - int.frac result (where frac has NUM_DENTS_FRAC_BITS)
+ *
+ * Side Effects:
+ *
+ *----------------------------------------------------------------------------
+*/
+EAS_I32 EAS_Calculate2toX (EAS_I32 nCents)
+{
+	EAS_I32 nDents;
+	EAS_I32 nExponentInt, nExponentFrac;
+	EAS_I32 nTemp1, nTemp2;
+	EAS_I32 nResult;
+
+	/* check for minimum value */
+	if (nCents < MIN_CENTS)
+		return 0;
+
+	/* for the time being, convert cents to dents */
+	nDents = FMUL_15x15(nCents, CENTS_TO_DENTS);
+
+	nExponentInt = GET_DENTS_INT_PART(nDents);
+	nExponentFrac = GET_DENTS_FRAC_PART(nDents);
+
+	/*
+	implement 2^(fracPart) as a power series
+	*/
+	nTemp1 = GN2_TO_X2 + MULT_DENTS_COEF(nExponentFrac, GN2_TO_X3);
+	nTemp2 = GN2_TO_X1 + MULT_DENTS_COEF(nExponentFrac, nTemp1);
+	nTemp1 = GN2_TO_X0 + MULT_DENTS_COEF(nExponentFrac, nTemp2);
+
+	/*
+	implement 2^(intPart) as 
+	a left shift for intPart >= 0 or
+	a left shift for intPart <  0
+	*/
+	if (nExponentInt >= 0)
+	{
+		/* left shift for positive exponents */
+		/*lint -e{703} <avoid multiply for performance>*/
+		nResult = nTemp1 << nExponentInt;
+	}
+	else
+	{
+		/* right shift for negative exponents */
+		nExponentInt = -nExponentInt;
+		nResult = nTemp1 >> nExponentInt;
+	}
+
+	return nResult;
+}
+
+/*----------------------------------------------------------------------------
+ * EAS_LogToLinear16()
+ *----------------------------------------------------------------------------
+ * Purpose:
+ * Transform log value to linear gain multiplier using piece-wise linear
+ * approximation
+ *
+ * Inputs:
+ * nGain - log scale value in 20.10 format. Even though gain is normally
+ * stored in 6.10 (16-bit) format we use 32-bit numbers here to eliminate
+ * the need for saturation checking when combining gain values.
+ *
+ * Outputs:
+ * Returns a 16-bit linear value approximately equal to 2^(nGain/1024)
+ *
+ * Side Effects:
+ *
+ *----------------------------------------------------------------------------
+*/
+EAS_U16 EAS_LogToLinear16 (EAS_I32 nGain)
+{
+	EAS_INT nExp;
+	EAS_U16 nTemp;
+
+	/* bias to positive */
+	nGain += 32767;
+
+	/* check for infinite attenuation */
+	if (nGain < 0)
+		return 0;
+
+	/* extract the exponent */
+	nExp = 31 - (nGain >> 10);
+
+	/* check for maximum output */
+	if (nExp < 0)
+		return 0x7fff;
+
+	/* extract mantissa and restore implied 1 bit */
+	nTemp = (EAS_U16)((((nGain & 0x3ff) << 4) | 0x4000) >> nExp);
+
+	/* use shift to approximate power-of-2 operation */
+	return nTemp;
+}
+
+/*----------------------------------------------------------------------------
+ * EAS_VolumeToGain()
+ *----------------------------------------------------------------------------
+ * Purpose:
+ * Transform volume control in 1dB increments to gain multiplier
+ *
+ * Inputs:
+ * volume - 100 = 0dB, 99 = -1dB, 0 = -inf
+ *
+ * Outputs:
+ * Returns a 16-bit linear value 
+ *----------------------------------------------------------------------------
+*/
+EAS_I16 EAS_VolumeToGain (EAS_INT volume)
+{
+	/* check for limits */
+	if (volume <= 0)
+		return 0;
+	if (volume >= 100)
+		return 0x7fff;
+	
+	/*lint -e{702} use shift instead of division */
+	return (EAS_I16) EAS_Calculate2toX((((volume - EAS_MAX_VOLUME) * 204099) >> 10) - 1);
+}
+