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  1. /*
  2.  * Copyright (C) 2010-2018 Arm Limited or its affiliates. All rights reserved.
  3.  *
  4.  * SPDX-License-Identifier: Apache-2.0
  5.  *
  6.  * Licensed under the Apache License, Version 2.0 (the License); you may
  7.  * not use this file except in compliance with the License.
  8.  * You may obtain a copy of the License at
  9.  *
  10.  * www.apache.org/licenses/LICENSE-2.0
  11.  *
  12.  * Unless required by applicable law or agreed to in writing, software
  13.  * distributed under the License is distributed on an AS IS BASIS, WITHOUT
  14.  * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  15.  * See the License for the specific language governing permissions and
  16.  * limitations under the License.
  17.  */
  18.  
  19. /* ----------------------------------------------------------------------
  20.  * Project:      CMSIS NN Library
  21.  * Title:        arm_nn_activations_q15.c
  22.  * Description:  Q15 neural network activation function using direct table look-up
  23.  *
  24.  * $Date:        17. January 2018
  25.  * $Revision:    V.1.0.0
  26.  *
  27.  * Target Processor:  Cortex-M cores
  28.  *
  29.  * -------------------------------------------------------------------- */
  30.  
  31. #include "arm_math.h"
  32. #include "arm_common_tables.h"
  33. #include "arm_nnfunctions.h"
  34.  
  35. /**
  36.  *  @ingroup groupNN
  37.  */
  38.  
  39. /**
  40.  * @addtogroup Acti
  41.  * @{
  42.  */
  43.  
  44.   /**
  45.    * @brief Q15 neural network activation function using direct table look-up
  46.    * @param[in,out]   data        pointer to input
  47.    * @param[in]       size        number of elements
  48.    * @param[in]       int_width   bit-width of the integer part, assume to be smaller than 3
  49.    * @param[in]       type        type of activation functions
  50.    * @return none.
  51.    *
  52.    * @details
  53.    *
  54.    * This is the direct table look-up approach.
  55.    *
  56.    * Assume here the integer part of the fixed-point is <= 3.
  57.    * More than 3 just not making much sense, makes no difference with
  58.    * saturation followed by any of these activation functions.
  59.    */
  60.  
  61. void arm_nn_activations_direct_q15(q15_t * data, uint16_t size, uint16_t int_width, arm_nn_activation_type type)
  62. {
  63.     uint16_t  i = size;
  64.     q15_t    *pIn = data;
  65.     q15_t    *pOut = data;
  66.     uint16_t  shift_size = 8 + 3 - int_width;
  67.     uint32_t  bit_mask = 0x7FF >> int_width;
  68.     uint32_t  full_frac = bit_mask + 1;
  69.     const q15_t *lookup_table;
  70.  
  71.     switch (type)
  72.     {
  73.     case ARM_SIGMOID:
  74.         lookup_table = sigmoidTable_q15;
  75.         break;
  76.     case ARM_TANH:
  77.     default:
  78.         lookup_table = tanhTable_q15;
  79.         break;
  80.     }
  81.  
  82.     while (i)
  83.     {
  84.         q15_t     out;
  85.         q15_t     in = *pIn++;
  86.         q15_t     frac = (uint32_t) in & bit_mask;
  87.         q15_t     value = lookup_table[__USAT(in >> shift_size, 8)];
  88.         q15_t     value2 = lookup_table[__USAT(1 + (in >> shift_size), 8)];
  89.  
  90.         /* doing the interpolation here for better accuracy */
  91.         out = ((q31_t) (full_frac - frac) * value + (q31_t) value2 * frac) >> shift_size;
  92.  
  93.         *pOut++ = out;
  94.         i--;
  95.     }
  96.  
  97. }
  98.  
  99. /**
  100.  * @} end of Acti group
  101.  */
  102.