dsps_dctiv_f32.c

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// Copyright 2018-2020 Espressif Systems (Shanghai) PTE LTD
//
// 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
//
//     http://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.
 
#include "dsp_common.h"
#include <math.h>
 
#include "dsps_dct.h"
#include "dsps_fft2r.h"
 
esp_err_t dsps_dctiv_f32(float *data, int ndct)
{
    if (dsps_fft2r_initialized == 0) {
        return ESP_ERR_DSP_REINITIALIZED;
    }
 
    float factor = M_PI / (ndct * 2);
    float in1, in2, in3, in4;
    for (int i = 0; i < ndct / 4; i++) {
        in1 = data[i * 2 + 0];
        in2 = data[i * 2 + 1];
        in3 = data[ndct - i * 2 - 1];
        in4 = data[ndct - i * 2 - 2];
 
        data[i * 2 + 0] = (
                              in1 * cos(factor * (i * 2 + 0))
                              + in3 * cos(factor * ((ndct - i * 2)))
                          );
 
        data[i * 2 + 1] = (
                              -in1 * sin(factor * (i * 2))
                              + in3 * sin(factor * ((ndct - i * 2)))
                          );
 
        data[ndct - i * 2 + 0 - 2] = (
                                         in2 * cos(factor * (i * 2 + 1 + 0.5) )
                                         + in4 * cos(factor * ((ndct - i * 2 - 1) - 0.5) )
                                     );
 
        data[ndct - i * 2 + 1 - 2] = (
                                         in2 * sin(factor * (i * 2 + 1))
                                         + in4 * sin(-factor * ((ndct - i * 2 - 1)) )
                                     );
 
    }
    esp_err_t error = ESP_OK;
    error = dsps_fft2r_fc32(data, ndct / 2);
    if (error != ESP_OK) {
        return error;
    }
    error = dsps_bit_rev_fc32(data, ndct / 2);
    if (error != ESP_OK) {
        return error;
    }
 
    for (int i = 0; i < ndct / 4; i++) {
        in1 = data[2 * i + 0];
        in2 = data[2 * i + 1];
 
        in3 = data[ndct - 2 * i - 2];
        in4 = data[ndct - 2 * i - 1];
 
        data[i * 2 + 0] = (
                              in1 * cos(factor * (0 + i * 2))
                              + in2 * sin(factor * (0 + i * 2))
                          );
 
        data[ndct  - i * 2 - 1] = (
                                      in1 * cos(factor * (ndct - i * 2))
                                      - in2 * sin(factor * (ndct - i * 2))
                                  );
 
        data[i * 2 + 1] = (
                              in3 * cos(factor * (2 + i * 2))
                              - in4 * sin(factor * (2 + i * 2))
                          );
 
        data[ndct  - i * 2 - 2] = (
                                      in3 * cos(factor * (ndct - i * 2 - 2) )
                                      + in4 * sin(factor * (ndct - i * 2 - 2) )
                                  );
    }
    return ESP_OK;
}