关于6678 dsplib ifft的问题

我安装的dsplib 版本为3.1.0.0，在测试fft和ifft时，fft调用DSPF_sp_fftDPxDP函数，ifft调用DSPF_sp_ifftDPxDP函数。

将结果和matlab输出的结果进行对比，发现DSPF_sp_fftDPxDP输出结果和matlab输出的结果一致，但DSPF_sp_ifftDPxDP的结果和matlab的结果不一样，而且将数据经过fft后再进行ifft，结果与原数据不一致。比较过数据ifft输出的数据与原数据无任何比例关系。

请问下有人知道这是为什么吗？

Shine：

看一下是不是归一化的问题？

user4436380：

回复 Shine:

代码如下，请帮我看下代码有没有问题：

#include <stdio.h>#include <stdlib.h>#include <stdint.h>#include <math.h>#include <c6x.h>#include <time.h>#include <ti/dsplib/src/DSPF_sp_fftSPxSP/c66/DSPF_sp_fftSPxSP.h>#include <ti/dsplib/src/DSPF_sp_ifftSPxSP/c66/DSPF_sp_ifftSPxSP.h>

#define N 32

#define PI 3.14159265358979323846

#pragma DATA_ALIGN(brev, 8);unsigned char brev[64] = { 0x0, 0x20, 0x10, 0x30, 0x8, 0x28, 0x18, 0x38, 0x4, 0x24, 0x14, 0x34, 0xc, 0x2c, 0x1c, 0x3c, 0x2, 0x22, 0x12, 0x32, 0xa, 0x2a, 0x1a, 0x3a, 0x6, 0x26, 0x16, 0x36, 0xe, 0x2e, 0x1e, 0x3e, 0x1, 0x21, 0x11, 0x31, 0x9, 0x29, 0x19, 0x39, 0x5, 0x25, 0x15, 0x35, 0xd, 0x2d, 0x1d, 0x3d, 0x3, 0x23, 0x13, 0x33, 0xb, 0x2b, 0x1b, 0x3b, 0x7, 0x27, 0x17, 0x37, 0xf, 0x2f, 0x1f, 0x3f};

#pragma DATA_ALIGN(f_src, 8);float f_src [2*N];#pragma DATA_ALIGN(f_out, 8);float f_out [2*N];#pragma DATA_ALIGN(f_tw, 8);float f_tw [2*N];

//static clock_t t_start, t_stop, t_overhead;

/* Function for generating Specialized sequence of twiddle factors */int gen_tw_1d_single (float *w, int n){ int i, j, k;

for (j = 1, k = 0; j <= n >> 2; j = j << 2) { for (i = 0; i < n >> 2; i += j) { w[k] = (float) sin (2 * PI * i / n); w[k + 1] = (float) cos (2 * PI * i / n); w[k + 2] = (float) sin (4 * PI * i / n); w[k + 3] = (float) cos (4 * PI * i / n); w[k + 4] = (float) sin (6 * PI * i / n); w[k + 5] = (float) cos (6 * PI * i / n); k += 6; } }

return k;}

void main(){ int loop;

for(loop = 0; loop < N ; loop ++) { f_src[loop * 2] = (float)(rand() % 16383); f_src[loop * 2 + 1] = 0; printf("%d\t", (int)f_src[loop * 2]); }

printf("\n");

gen_tw_1d_single(f_tw, N);

//TSCL=0;TSCH=0; // t_start = _itoll(TSCH, TSCL);

/* * @param N length of FFT in complex samples * @param ptr_x pointer to complex data input * @param ptr_w pointer to complex twiddle factor * @param ptr_y pointer to complex output data * @param brev pointer to bit reverse table containing 64 entries * @param n_min should be 4 if N can be represented as Power of 4 else, n_min should be 2 * @param offset index in complex samples of sub-fft from start of main fft * @param n_max size of main fft in complex samples */

//DSPF_sp_fftSPxSP_cn(N, f_src , f_tw, f_out, brev, 4, 0, N); DSPF_sp_fftSPxSP(N, f_src , f_tw, f_out, brev, 4, 0, N); //t_stop = _itoll(TSCH, TSCL); //t_overhead = t_stop – t_start;

for(loop = 0; loop < N * 2; loop ++) { f_src[loop] = f_out[loop]/N; } // printf("Cycle Consumed :%d\nTime Consumed:%f ms\n\n", t_overhead, (float)t_overhead / CYCLEPERMS);

/* * @param N length of FFT in complex samples * @param ptr_x pointer to complex data input * @param ptr_w pointer to complex twiddle factor * @param ptr_y pointer to complex output data * @param brev pointer to bit reverse table containing 64 entries * @param n_min should be 4 if N can be represented as Power of 4 else, n_min should be 2 * @param offset index in complex samples of sub-fft from start of main fft * @param n_max size of main fft in complex samples * */ DSPF_sp_ifftSPxSP(N, f_src , f_tw, f_out, brev, 4, 0, N);

for(loop = 0; loop < N; loop ++) { printf("%d\t", (int)f_out[loop * 2]); }

printf("\n");}

user4436380：

回复 Shine:

已经做了归一化处理。