arm_nn_activations_q15.c

00001 /*
00002  * Copyright (C) 2010-2018 Arm Limited or its affiliates. All rights reserved.
00003  *
00004  * SPDX-License-Identifier: Apache-2.0
00005  *
00006  * Licensed under the Apache License, Version 2.0 (the License); you may
00007  * not use this file except in compliance with the License.
00008  * You may obtain a copy of the License at
00009  *
00010  * www.apache.org/licenses/LICENSE-2.0
00011  *
00012  * Unless required by applicable law or agreed to in writing, software
00013  * distributed under the License is distributed on an AS IS BASIS, WITHOUT
00014  * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
00015  * See the License for the specific language governing permissions and
00016  * limitations under the License.
00017  */
00018 
00019 /* ----------------------------------------------------------------------
00020  * Project:      CMSIS NN Library
00021  * Title:        arm_nn_activations_q15.c
00022  * Description:  Q15 neural network activation function using direct table look-up
00023  *
00024  * $Date:        17. January 2018
00025  * $Revision:    V.1.0.0
00026  *
00027  * Target Processor:  Cortex-M cores
00028  *
00029  * -------------------------------------------------------------------- */
00030 
00031 #include "arm_math.h"
00032 #include "arm_common_tables.h"
00033 #include "arm_nnfunctions.h"
00034 
00035 /**
00036  *  @ingroup groupNN
00037  */
00038 
00039 /**
00040  * @addtogroup Acti
00041  * @{
00042  */
00043 
00044   /**
00045    * @brief Q15 neural network activation function using direct table look-up
00046    * @param[in,out]   data        pointer to input
00047    * @param[in]       size        number of elements
00048    * @param[in]       int_width   bit-width of the integer part, assume to be smaller than 3
00049    * @param[in]       type        type of activation functions
00050    * @return none.
00051    *
00052    * @details
00053    * 
00054    * This is the direct table look-up approach.
00055    *
00056    * Assume here the integer part of the fixed-point is <= 3.
00057    * More than 3 just not making much sense, makes no difference with
00058    * saturation followed by any of these activation functions. 
00059    */
00060 
00061 void arm_nn_activations_direct_q15(q15_t * data, uint16_t size, uint16_t int_width, arm_nn_activation_type type)
00062 {
00063     uint16_t  i = size;
00064     q15_t    *pIn = data;
00065     q15_t    *pOut = data;
00066     uint16_t  shift_size = 8 + 3 - int_width;
00067     uint32_t  bit_mask = 0x7FF >> int_width;
00068     uint32_t  full_frac = bit_mask + 1;
00069     const q15_t *lookup_table;
00070 
00071     switch (type)
00072     {
00073     case ARM_SIGMOID:
00074         lookup_table = sigmoidTable_q15;
00075         break;
00076     case ARM_TANH:
00077     default:
00078         lookup_table = tanhTable_q15;
00079         break;
00080     }
00081 
00082     while (i)
00083     {
00084         q15_t     out;
00085         q15_t     in = *pIn++;
00086         q15_t     frac = (uint32_t) in & bit_mask;
00087         q15_t     value = lookup_table[__USAT(in >> shift_size, 8)];
00088         q15_t     value2 = lookup_table[__USAT(1 + (in >> shift_size), 8)];
00089 
00090         /* doing the interpolation here for better accuracy */
00091         out = ((q31_t) (full_frac - frac) * value + (q31_t) value2 * frac) >> shift_size;
00092 
00093         *pOut++ = out;
00094         i--;
00095     }
00096 
00097 }
00098 
00099 /**
00100  * @} end of Acti group
00101  */
00102