/github/workspace/src/TransformFunctions/plp_dct2_f32.c

Functions

	Name
void	plp_dct2_f32(const plp_fft_instance_f32 * S, const Complex_type_f32 * pShift, const uint8_t orthoNorm, const float32_t restrict pSrc, float32_t restrict pBuf, float32_t *restrict pDst) Floating-point DCT on real input data. Implementation of John Makhoul's "A Fast Cosine Transform in One and Two Dimensions" 1980 IEEE paper.

Functions Documentation

function plp_dct2_f32

void plp_dct2_f32(
    const plp_fft_instance_f32 * S,
    const Complex_type_f32 * pShift,
    const uint8_t orthoNorm,
    const float32_t *__restrict__ pSrc,
    float32_t *__restrict__ pBuf,
    float32_t *__restrict__ pDst
)

Floating-point DCT on real input data. Implementation of John Makhoul's "A Fast Cosine Transform in One and Two Dimensions" 1980 IEEE paper.

Parameters:

• S points to an instance of the floating-point FFT structure with FFTLength = DCTLength
• pShift points to twiddle coefficient table of 4*FFTLength, of which only the first quadrant of the complex unit circle is used. For example, if S contains twiddleCoef_rfft_32, pShift can be set to twiddleCoef_rfft_128.
• pSrc points to the input buffer (real data) of size FFTLength.
• pBuf points to buffer of size 2*FFTLength, used for computation.
• pDst points to output buffer (real data) of size FFTLength, may be the same as pSrc.

Return: none

Source code

/* ----------------------------------------------------------------------
 * Project:      PULP DSP Library
 * Title:        plp_dct2_f32.c
 * Description:  Floating-point DCT of type 2 on real input data
 *
 * $Date:        04. July 2021
 * $Revision:    V0
 *
 * Target Processor: PULP cores with "F" support (wolfe, vega)
 * -------------------------------------------------------------------- */
/*
 * Copyright (C) 2019 ETH Zurich and University of Bologna. All rights reserved.
 *
 * Author: Aron Szakacs, ETH Zürich
 *
 * 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.
 */

#include "plp_math.h"

void plp_dct2_f32(const plp_fft_instance_f32 *S,
                  const Complex_type_f32 *pShift,
          const uint8_t orthoNorm,
                  const float32_t *__restrict__ pSrc,
                  float32_t *__restrict__ pBuf,
                  float32_t *__restrict__ pDst) {

    // 1: reordering (moves input from pSrc to pDst)
    uint32_t N = S->FFTLength;
    // write odd indices from Src into buffer
    for (int i=0;i<N/2;i++){
    pBuf[i] = pSrc[2*i + 1];
    }
    // squeeze remaining even indices closer together (decimate signal to odd indices) and write into Dst
    for (int i=0;i<N/2;i++){
    pDst[i] = pSrc[2*i];
    }
    // reverse and write saved odd indices into second half of Dst
    for (int i=0;i<N/2;i++){
    pDst[N/2+i] = pBuf[N/2-1-i];
    }
    // 2: RFFT of reordered sequence, result written into buffer
    plp_rfft_f32(S, pDst, pBuf);
    // RFFT must be extended to all FFTLength complex coefficients,
    // using X[k] = X*[-k] for real x[t]
    for (int i=0;i<N/2-1;i++) {
    pBuf[2*(N/2+1+i)] = pBuf[2*(N/2-1-i)];
    pBuf[2*(N/2+1+i)+1] = (-1)*pBuf[2*(N/2-1-i)+1];
    }
    // 3: shift FFT in place in buffer
    plp_cmplx_mult_cmplx_f32(pBuf, (float32_t*)pShift, pBuf, N);
    // 4: take real part, moving from buffer to output
    for (int i=0;i<N;i++){
    pDst[i] = pBuf[2*i];
    }
    // 5: multiply by 2 or normalise in place in output buffer
    if (orthoNorm) {
    pDst[0] *= M_SQRT1_2;
    plp_scale_f32(pDst, sqrtf(2.f/(float32_t)N), pDst, N);
    }
    else
        plp_scale_f32(pDst, 2, pDst, N);
}

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Updated on 2023-03-01 at 16:16:33 +0000