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Drivers/CMSIS/NN/Source/SoftmaxFunctions/arm_softmax_u8.c

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+/*
+ * Copyright (C) 2010-2020 Arm Limited or its affiliates. All rights reserved.
+ *
+ * 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_u8.c
+ * Description:  U8 softmax function
+ *
+ * $Date:        09. October 2020
+ * $Revision:    V.1.0.2
+ *
+ * Target Processor:  Cortex-M CPUs
+ *
+ * -------------------------------------------------------------------- */
+
+#include "arm_nnfunctions.h"
+#include "arm_nnsupportfunctions.h"
+
+#define ACCUM_BITS 12
+
+/**
+ *  @ingroup groupNN
+ */
+
+/**
+ * @addtogroup Softmax
+ * @{
+ */
+void arm_softmax_u8(const uint8_t *input,
+                    const int32_t num_rows,
+                    const int32_t row_size,
+                    const int32_t mult,
+                    const int32_t shift,
+                    const int32_t diff_min,
+                    uint8_t *output)
+{
+    const int32_t mask = (1 << shift);
+
+    int32_t col = 0;
+    int32_t row_idx;
+
+    for (row_idx = 0; row_idx < num_rows; ++row_idx)
+    {
+        // Find the maximum value in order to ensure numerical stability
+        uint8_t max = *input;
+
+        for (col = 1; col < row_size; ++col)
+        {
+            max = MAX(max, input[col]);
+        }
+
+        int32_t diff = 0;
+        int32_t sum = 0;
+
+        for (col = 0; col < row_size; ++col)
+        {
+            diff = input[col] - max;
+            if (diff >= diff_min)
+            {
+                sum += DIV_POW2(EXP_ON_NEG(MUL_SAT(diff * mask, mult)), ACCUM_BITS);
+            }
+        }
+
+        const int32_t headroom = __CLZ((uint32_t)sum);
+        const int32_t bits_over_unit = ACCUM_BITS - headroom + 23;
+        const int32_t shifted_scale = ONE_OVER1((sum << headroom) - (1 << 31));
+
+        for (col = 0; col < row_size; ++col)
+        {
+            diff = input[col] - max;
+            if (diff >= diff_min)
+            {
+                const int32_t res =
+                    DIV_POW2(MUL_SAT(shifted_scale, EXP_ON_NEG(MUL_SAT(diff * mask, mult))), bits_over_unit);
+                output[col] = (uint8_t)CLAMP(res, (int32_t)255, (int32_t)0);
+            }
+            else
+            {
+                output[col] = 0;
+            }
+        }
+        input += row_size;
+        output += row_size;
+    }
+}
+/**
+ * @} end of Softmax group
+ */