ref: 02fa913c32f43a3855db4ccc98b87f3018f672db
dir: /libcelt/mdct.c/
/* (C) 2008 Jean-Marc Valin, CSIRO */ /* Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: - Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. - Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. - Neither the name of the Xiph.org Foundation nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ /* This is a simple MDCT implementation that uses a N/4 complex FFT to do most of the work. It should be relatively straightforward to plug in pretty much and FFT here. This replaces the Vorbis FFT (and uses the exact same API), which was a bit too messy and that was ending up duplicating code (might as well use the same FFT everywhere). The algorithm is similar to (and inspired from) Fabrice Bellard's MDCT implementation in FFMPEG, but has differences in signs, ordering and scaling in many places. */ #ifdef HAVE_CONFIG_H #include "config.h" #endif #include "mdct.h" #include "kiss_fft.h" #include <math.h> #include "os_support.h" #ifndef M_PI #define M_PI 3.14159263 #endif void mdct_init(mdct_lookup *l,int N) { int i; int N2, N4; l->n = N; N2 = N/2; N4 = N/4; l->kfft = kiss_fft_alloc(N4, NULL, NULL); l->trig = celt_alloc(N2*sizeof(float)); /* We have enough points that sine isn't necessary */ for (i=0;i<N2;i++) l->trig[i] = cos(2*M_PI*(i+1./8.)/N); l->scale = 1./N4; } void mdct_clear(mdct_lookup *l) { kiss_fft_free(l->kfft); celt_free(l->trig); } void mdct_forward(mdct_lookup *l, float *in, float *out) { int i; int N, N2, N4, N8; N = l->n; N2 = N/2; N4 = N/4; N8 = N/8; float f[N2]; /* Consider the input to be compused of four blocks: [a, b, c, d] */ /* Shuffle, fold, pre-rotate (part 1) */ for(i=0;i<N8;i++) { float re, im; /* Real part arranged as -d-cR, Imag part arranged as -b+aR*/ re = -in[N2+N4+2*i] - in[N2+N4-2*i-1]; im = -in[N4+2*i] + in[N4-2*i-1]; out[2*i] = re*l->trig[i] - im*l->trig[i+N4]; out[2*i+1] = im*l->trig[i] + re*l->trig[i+N4]; } for(;i<N4;i++) { float re, im; /* Real part arranged as a-bR, Imag part arranged as -c-dR */ re = in[2*i-N4] - in[N2+N4-2*i-1]; im = -(in[N4+2*i] + in[N+N4-2*i-1]); out[2*i] = re*l->trig[i] - im*l->trig[i+N4]; out[2*i+1] = im*l->trig[i] + re*l->trig[i+N4]; } /* N/4 complex FFT, which should normally down-scale by 4/N (but doesn't now) */ kiss_fft(l->kfft, (const kiss_fft_cpx *)out, (kiss_fft_cpx *)f); /* Post-rotate and apply the scaling if the FFT doesn't to it itself */ for(i=0;i<N4;i++) { out[2*i] = l->scale * (-f[2*i+1]*l->trig[i+N4] + f[2*i] *l->trig[i]); out[N2-1-2*i] = l->scale * (-f[2*i] *l->trig[i+N4] - f[2*i+1]*l->trig[i]); } } void mdct_backward(mdct_lookup *l, float *in, float *out) { int i; int N, N2, N4, N8; N = l->n; N2 = N/2; N4 = N/4; N8 = N/8; float f[N2]; /* Pre-rotate */ for(i=0;i<N4;i++) { out[2*i] = -in[N2-2*i-1] * l->trig[i] - in[2*i]*l->trig[i+N4]; out[2*i+1] = in[N2-2*i-1] * l->trig[i+N4] - in[2*i]*l->trig[i]; } /* Inverse N/4 complex FFT. This one should *not* downscale even in fixed-point */ kiss_ifft(l->kfft, (const kiss_fft_cpx *)out, (kiss_fft_cpx *)f); /* Post-rotate */ for(i=0;i<N4;i++) { float re, im; re = f[2*i]; im = f[2*i+1]; f[2*i] = re*l->trig[i] + im*l->trig[i+N4]; f[2*i+1] = im*l->trig[i] - re*l->trig[i+N4]; } /* De-shuffle the components for the middle of the window only */ for(i = 0; i < N4; i++) { out[N4+2*i] =-f[2*i]; out[N4+2*i+1] = f[N2-2*i-1]; } /* Mirror on both sides for TDAC */ for(i = 0; i < N4; i++) { out[i] =-out[N2-i-1]; out[N-i-1] = out[N2+i]; } }