dsps_dctiv_f32.c File Reference

#include "dsp_common.h"
#include <math.h>
#include "dsps_dct.h"
#include "dsps_fft2r.h"

Include dependency graph for dsps_dctiv_f32.c:

Go to the source code of this file.

Functions
esp_err_t	dsps_dctiv_f32 (float *data, int ndct)
	DCT of radix 2, type IV, unscaled.

Function Documentation

dsps_dctiv_f32()

esp_err_t dsps_dctiv_f32	(	float *	data,
		int	N )

DCT of radix 2, type IV, unscaled.

Discrete Cosine Transform type IV of radix 2, unscaled Function is FFT based The extension (_ansi) use ANSI C and could be compiled and run on any platform. The extension (_ae32) is optimized for ESP32 chip.

Parameters

[in,out]	data	input/output array with size of N. An elements located: Re[0],Re[1], , ... Re[N-1] result of DST will be stored to this array from 0...N-1. Size of data array must be N
[in]	N	Size of DCT transform. Size of data array must be N

Returns

• ESP_OK on success
• One of the error codes from DSP library

Definition at line 21 of file dsps_dctiv_f32.c.

{
    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;
}

References data, dsps_bit_rev_fc32, dsps_fft2r_fc32, dsps_fft2r_initialized, ESP_ERR_DSP_REINITIALIZED, ESP_OK, and M_PI.