123 lines
4.3 KiB
C
123 lines
4.3 KiB
C
/*
|
|
* Copyright (C) 2022 Arm Limited or its affiliates.
|
|
*
|
|
* SPDX-License-Identifier: Apache-2.0
|
|
*
|
|
* 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
|
|
*
|
|
* 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.
|
|
*/
|
|
|
|
/* ----------------------------------------------------------------------
|
|
* Project: CMSIS NN Library
|
|
* Title: arm_softmax_s16.c
|
|
* Description: S16 softmax function
|
|
*
|
|
* $Date: 9 March 2022
|
|
* $Revision: V.1.0.0
|
|
*
|
|
* Target Processor: Cortex-M cores
|
|
*
|
|
* -------------------------------------------------------------------- */
|
|
|
|
#include "arm_nnfunctions.h"
|
|
#include "arm_nnsupportfunctions.h"
|
|
|
|
/**
|
|
* @addtogroup Softmax
|
|
* @{
|
|
*/
|
|
|
|
arm_status arm_softmax_s16(const int16_t *input,
|
|
const int32_t num_rows,
|
|
const int32_t row_size,
|
|
const int32_t mult,
|
|
const int32_t shift,
|
|
const cmsis_nn_softmax_lut_s16 *softmax_params,
|
|
int16_t *output)
|
|
{
|
|
int32_t col = 0;
|
|
int32_t row_idx;
|
|
|
|
if (softmax_params->exp_lut == NULL || softmax_params->one_by_one_lut == NULL)
|
|
{
|
|
return ARM_MATH_ARGUMENT_ERROR;
|
|
}
|
|
|
|
for (row_idx = 0; row_idx < num_rows; ++row_idx)
|
|
{
|
|
// Find the maximum value in order to ensure numerical stability
|
|
int16_t max = *input;
|
|
for (col = 1; col < row_size; ++col)
|
|
{
|
|
max = MAX(max, input[col]);
|
|
}
|
|
|
|
int32_t diff = 0;
|
|
int32_t sum = 0;
|
|
int16_t *cached_exp_results = output;
|
|
|
|
for (col = 0; col < row_size; ++col)
|
|
{
|
|
diff = input[col] - max;
|
|
const int32_t scaled_diff = arm_nn_requantize(diff, mult, shift);
|
|
const int32_t symmetric_scaled_diff = scaled_diff + NN_Q15_MAX;
|
|
const int16_t saturated_symmetric_scaled_diff = MIN(MAX(symmetric_scaled_diff, NN_Q15_MIN), NN_Q15_MAX);
|
|
|
|
// Lookup from exp table and cache result for next step
|
|
const int16_t index = (256 + (saturated_symmetric_scaled_diff >> 7));
|
|
const int16_t offset = saturated_symmetric_scaled_diff & 0x7f;
|
|
const int16_t base = softmax_params->exp_lut[index];
|
|
const int16_t slope = softmax_params->exp_lut[index + 1] - softmax_params->exp_lut[index];
|
|
const int16_t delta = (slope * offset + 64) >> 7;
|
|
const int16_t result = (base + delta);
|
|
cached_exp_results[col] = result;
|
|
|
|
sum += cached_exp_results[col];
|
|
}
|
|
|
|
const int32_t headroom = __CLZ(sum);
|
|
|
|
// Compute the reciprocal 1/sum
|
|
const int32_t shifted_sum = (((sum) << (headroom - 1)) + (1 << 13)) >> 14;
|
|
|
|
// Since LUT computes 1/(1 + x), compute x = (sum - 1) => -65536
|
|
// Since LUT expects a symmetrical input, recenter from [UINT16_MIN, UINT16_MAX] to [INT16_MIN, INT16_MAX] =>
|
|
// -32768 ==> So in total -65536 -32768 => -98304
|
|
const int16_t symmetric_shifted_sum = shifted_sum - 98304;
|
|
|
|
// Lookup from one by one table
|
|
const int16_t index = (256 + (symmetric_shifted_sum >> 7));
|
|
const int16_t offset = symmetric_shifted_sum & 0x7f;
|
|
const int16_t base = softmax_params->one_by_one_lut[index];
|
|
const int16_t slope = softmax_params->one_by_one_lut[index + 1] - softmax_params->one_by_one_lut[index];
|
|
const int16_t delta = (slope * offset + 64) >> 7;
|
|
const int16_t one_by_one_result = (base + delta);
|
|
|
|
for (col = 0; col < row_size; ++col)
|
|
{
|
|
const int16_t right_shift = 30 - headroom;
|
|
int32_t result = (cached_exp_results[col] * one_by_one_result) >> right_shift;
|
|
result = (result + 1) >> 1; // Last shift position and insert round
|
|
output[col] = (int16_t)result;
|
|
}
|
|
|
|
output += row_size;
|
|
input += row_size;
|
|
}
|
|
|
|
return ARM_MATH_SUCCESS;
|
|
}
|
|
|
|
/**
|
|
* @} end of Softmax group
|
|
*/
|