MATHLIB_log_scalar.h

Go to the documentation of this file.

/******************************************************************************
 * Copyright (C) 2023 Texas Instruments Incorporated - https://www.ti.com/
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *    Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 *    Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the
 *    distribution.
 *
 *    Neither the name of Texas Instruments Incorporated nor the names of
 *    its contributors may be used to endorse or promote products derived
 *    from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 ******************************************************************************/
 
#ifndef MATHLIB_LOG_SCALAR_H_
#define MATHLIB_LOG_SCALAR_H_
 
/******************************************************************************/
/*                                                                            */
/* Includes                                                                   */
/*                                                                            */
/******************************************************************************/
 
#include "../common/MATHLIB_scalarTables.h"
#include "../common/MATHLIB_types.h"
#include "c6x_migration.h"
 
/******************************************************************************/
/*                                                                            */
/* Scalar/C6x implementation of log                                           */
/*                                                                            */
/******************************************************************************/
 
static inline float MATHLIB_log_scalar_ci(float a)
{
   double       ln2  = 0.693147180559945f;
   float        c1   = -0.2302894f;
   float        c2   = 0.1908169f;
   float        c3   = -0.2505905f;
   float        c4   = 0.3333164f;
   float        c5   = -0.5000002f;
   float        MAXe = 3.402823466E+38f;
   float        pol, r1, r2, r3, r4, res;
   double       dr, frcpax, rcp, T;
   unsigned int T_index;
   int          N;
 
   /* r = x * frcpa(x) -1 */
   rcp    = _rcpdp((double) a);
   frcpax = _itod(_clr(_hi(rcp), 0u, 16u), 0u);
   dr     = (frcpax * (double) a) - 1.0;
 
   /* Polynomial p(r) that approximates ln(1+r) - r */
   r1 = (float) dr;
   r2 = r1 * r1;
   r3 = r1 * r2;
   r4 = r2 * r2;
 
   pol = (c5 * r2) + ((c4 * r3) + ((((c2 * r1) + c3) + (c1 * r2)) * r4));
 
   /* Reconstruction: result = T + r + p(r) */
   N       = (int) _extu(_hi(frcpax), 1u, 21u) - 1023;
   T_index = _extu(_hi(frcpax), 12u, 29u);
   T       = MATHLIB_logTable[T_index] - (ln2 * (double) N);
   res     = (float) (dr + T) + pol;
 
   if (a <= 0.0f) {
      res = _itof(0xFF800000u);
   }
   if (a > MAXe) {
      res = 709.7827f;
   }
 
   return (res);
}
 
#endif // MATHLIB_LOG_SCALAR_H_