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Merged
lgirdwood merged 1 commit into from
Feb 11, 2025
Merged

Math: Replace exp() function with more accurate and fast version #9786

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61 changes: 31 additions & 30 deletions src/include/sof/math/exp_fcn.h
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Original file line number Diff line number Diff line change
@@ -1,8 +1,9 @@
/* SPDX-License-Identifier: BSD-3-Clause
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*
* Copyright(c) 2022 Intel Corporation. All rights reserved.
* Copyright(c) 2022-2025 Intel Corporation.
*
* Author: Shriram Shastry <[email protected]>
* Seppo Ingalsuo <[email protected]>
*
*/
#ifndef __SOFM_EXP_FCN_H__
Expand All @@ -26,40 +27,40 @@

#endif

/* TODO: Is there a MCPS difference */
#define USING_QCONVERT 1
/* Q5.27 int32(round(log((2^31 - 1)/2^20) * 2^27)) */
#define SOFM_EXP_FIXED_INPUT_MAX 1023359037

#if USING_QCONVERT
/* Q8.24 int32(round((log((2^31 - 1)/2^20) * 20 / log(10)) * 2^24)) */
#define SOFM_DB2LIN_INPUT_MAX 1111097957

#include <sof/audio/format.h>
#define SOFM_EXP_FIXED_INPUT_MIN Q_CONVERT_FLOAT(-11.5, 27) /* Q5.27 */
#define SOFM_EXP_FIXED_INPUT_MAX Q_CONVERT_FLOAT(7.6245, 27) /* Q5.27 */
#define SOFM_EXP_TWO_Q27 Q_CONVERT_FLOAT(2.0, 27) /* Q5.27 */
#define SOFM_EXP_MINUS_TWO_Q27 Q_CONVERT_FLOAT(-2.0, 27) /* Q5.27 */
#define SOFM_EXP_ONE_Q20 Q_CONVERT_FLOAT(1.0, 20) /* Q12.20 */
#define SOFM_EXP_MINUS_100_Q24 Q_CONVERT_FLOAT(-100.0, 24) /* Q8.24 */
#define SOFM_EXP_LOG10_DIV20_Q27 Q_CONVERT_FLOAT(0.1151292546, 27) /* Q5.27 */

#else

#define SOFM_EXP_FIXED_INPUT_MIN -1543503872 /* Q_CONVERT_FLOAT(-11.5, 27) */
#define SOFM_EXP_FIXED_INPUT_MAX 1023343067 /* Q_CONVERT_FLOAT(7.6245, 27) */
#define SOFM_EXP_TWO_Q27 268435456 /* Q_CONVERT_FLOAT(2.0, 27) */
#define SOFM_EXP_MINUS_TWO_Q27 -268435456 /* Q_CONVERT_FLOAT(-2.0, 27) */
#define SOFM_EXP_ONE_Q20 1048576 /* Q_CONVERT_FLOAT(1.0, 20) */
#define SOFM_EXP_MINUS_100_Q24 -1677721600 /* Q_CONVERT_FLOAT(-100.0, 24) */
#define SOFM_EXP_LOG10_DIV20_Q27 15452387 /* Q_CONVERT_FLOAT(0.1151292546, 27) */
/**
* Calculates exponent function exp(x) = e^x with accurate and efficient technique that
* includes range reduction operations, approximation with Taylor series, and reconstruction
* operations to compensate the range reductions.
* @param x The input argument as Q4.28 from -8 to +8
* @return The calculated e^x value as Q13.19 from 3.3546e-04 to 2981.0
*/
int32_t sofm_exp_approx(int32_t x);

#endif
/**
* Calculated exponent function exp(x) = e^x by using sofm_exp_approx(). The input range for
* large arguments is internally reduced to -8 to +8 with rule exp(x) = exp(x/2) * exp(x/2)
* and reconstructed back. This function is essentially a wrapper for compatibility with
* existing usage of exp() function and Q-format choice. Note that the return value saturates
* to INT32_MAX with input arguments larger than 7.6246.
* @param x The input argument as Q5.27 from -16 to +16
* @return The calculated e^x value as Q12.20
*/
int32_t sofm_exp_fixed(int32_t x);

#define SOFM_EXP_BIT_MASK_LOW_Q27P5 0x0000000008000000
#define SOFM_EXP_BIT_MASK_Q62P2 0x4000000000000000LL
#define SOFM_EXP_QUOTIENT_SCALE 0x40000000
#define SOFM_EXP_TERMS_Q23P9 0x800000
#define SOFM_EXP_LSHIFT_BITS 0x2000

int32_t sofm_exp_int32(int32_t x);
int32_t sofm_exp_fixed(int32_t x);
/**
* Converts a decibels value to liner amplitude lin = 10^(db/20) value with optimized
* equation exp(db * log(10)/20). Note that due to range limitation of sofm_exp_fixed()
* the output saturates to maximum with about +66 dB input.
* @param db Decibels value in Q8.24 format, from -128 to +66.226
* @return Linear value in Q12.20 format, from 3.9811e-07 to 2048
*/
int32_t sofm_db2lin_fixed(int32_t db);

#endif /* __SOFM_EXP_FCN_H__ */
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