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Improvement: removed extraneous memory copy in fft implementation.

This commit is contained in:
Anne de Jong 2018-02-27 19:00:58 +01:00 committed by Anne de Jong
parent c55d3b1e17
commit ccda090266
1 changed files with 30 additions and 40 deletions
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70
lasp/c/lasp_fft.c
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@ -14,14 +14,12 @@
typedef struct Fft_s {
us nfft;
vd fft_work;
vd fft_result; /**< Temporary storage for the FFT
* result */
} Fft;
Fft* Fft_create(const us nfft) {
fsTRACE(15);
if(nfft == 0) {
WARN("nfft > 0");
WARN("nfft should be > 0");
return NULL;
}
@ -35,7 +33,6 @@ Fft* Fft_create(const us nfft) {
/* Initialize foreign fft lib */
fft->fft_work = vd_alloc(2*nfft+15);
fft->fft_result = vd_alloc(nfft);
npy_rffti(nfft,getvdval(&fft->fft_work,0));
check_overflow_vx(fft->fft_work);
@ -49,7 +46,6 @@ void Fft_free(Fft* fft) {
fsTRACE(15);
dbgassert(fft,NULLPTRDEREF);
vd_free(&fft->fft_work);
vd_free(&fft->fft_result);
a_free(fft);
feTRACE(15);
}
@ -66,29 +62,23 @@ void Fft_ifft_single(const Fft* fft,const vc* freqdata,vd* result) {
" result array");
/* Obtain fft_result */
vd fft_result = fft->fft_result;
d* freqdata_ptr = (d*) getvcval(freqdata,0);
d* result_ptr = getvdval(result,0);
/* Copy freqdata, to fft_result. */
d* fft_result_ptr = getvdval(&fft_result,0);
*fft_result_ptr = c_real(*getvcval(freqdata,0));
d_copy(&result_ptr[1],&freqdata_ptr[2],nfft-1);
result_ptr[0] = freqdata_ptr[0];
d_copy(&fft_result_ptr[1],
(d*) getvcval(freqdata,1),
nfft-1);
/* Perform backward transform */
/* Perform inplace backward transform */
npy_rfftb(nfft,
fft_result_ptr,
result_ptr,
getvdval(&fft->fft_work,0));
/* Scale by dividing by nfft. Checked with numpy implementation
* that this indeed needs to be done. */
d_scale(fft_result_ptr,1/((d) nfft),nfft);
* that this indeed needs to be done for FFTpack. */
d_scale(result_ptr,1/((d) nfft),nfft);
vd_copy(result,
&fft_result);
check_overflow_vx(*result);
feTRACE(15);
}
void Fft_ifft(const Fft* fft,const cmat* freqdata,dmat* timedata) {
@ -130,36 +120,36 @@ void Fft_fft_single(const Fft* fft,const vd* timedata,vc* result) {
dbgassert(result->size == (nfft/2+1),"Invalid number of rows in"
" result array");
/* Obtain fft_result */
vd fft_result = fft->fft_result;
/* Copy timedata, as it will be overwritten in the fft pass. */
vd_copy(&fft_result,timedata);
/* Perform fft */
npy_rfftf(nfft,getvdval(&fft_result,0),
getvdval(&fft->fft_work,0));
d* result_ptr = (d*) getvcval(result,0);
/* Fftpack stores the data a bit strange, the resulting array
* has the DC value at 0,the first cosine at 1, the first sine
* at 2 etc. This needs to be shifted properly in the
* at 2 etc. 1
* resulting matrix, as for the complex data, the imaginary
* part of the DC component equals zero. */
*getvcval(result,0) = *getvdval(&fft_result,0);
/* Copy timedata, as it will be overwritten in the fft pass. */
d_copy(&result_ptr[1],getvdval(timedata,0),nfft);
/* Perform fft */
npy_rfftf(nfft,&result_ptr[1],
getvdval(&fft->fft_work,0));
/* Set real part of DC component to first index of the rfft
* routine */
result_ptr[0] = result_ptr[1];
result_ptr[1] = 0; /* Set imaginary part of DC component
* to zero */
/* For an even fft, the imaginary part of the Nyquist frequency
* bin equals zero.*/
if(likely(nfft%2 == 0)) {
((d*) getvcval(result,nfft/2))[1] = 0;
result_ptr[nfft+1] = 0;
}
memcpy((void*) getvcval(result,1),
(void*) getvdval(&fft_result,1),
(nfft-1)*sizeof(d));
/* Set imaginary part of Nyquist frequency to zero */
check_overflow_vx(fft_result);
check_overflow_vx(*result);
check_overflow_vx(fft->fft_work);
feTRACE(15);
@ -185,7 +175,7 @@ void Fft_fft(const Fft* fft,const dmat* timedata,cmat* result) {
vc_free(&result_col);
}
check_overflow_xmat(*timedata);
check_overflow_xmat(*result);
check_overflow_xmat(*result);
feTRACE(15);
}