3 * Copyright (c) 2009 Alex Converse <alex dot converse at gmail dot com>
5 * This file is part of FFmpeg.
7 * FFmpeg is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
12 * FFmpeg is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Lesser General Public License for more details.
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with FFmpeg; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
23 #include "libavutil/mathematics.h"
28 * (Inverse) Real Discrete Fourier Transforms.
31 /* sin(2*pi*x/n) for 0<=x<n/4, followed by n/2<=x<3n/4 */
32 #if !CONFIG_HARDCODED_TABLES
47 static SINTABLE_CONST FFTSample
* const ff_sin_tabs
[] = {
48 NULL
, NULL
, NULL
, NULL
,
49 ff_sin_16
, ff_sin_32
, ff_sin_64
, ff_sin_128
, ff_sin_256
, ff_sin_512
, ff_sin_1024
,
50 ff_sin_2048
, ff_sin_4096
, ff_sin_8192
, ff_sin_16384
, ff_sin_32768
, ff_sin_65536
,
53 /** Map one real FFT into two parallel real even and odd FFTs. Then interleave
54 * the two real FFTs into one complex FFT. Unmangle the results.
55 * ref: http://www.engineeringproductivitytools.com/stuff/T0001/PT10.HTM
57 static void rdft_calc_c(RDFTContext
*s
, FFTSample
*data
)
61 const int n
= 1 << s
->nbits
;
63 const float k2
= 0.5 - s
->inverse
;
64 const FFTSample
*tcos
= s
->tcos
;
65 const FFTSample
*tsin
= s
->tsin
;
68 s
->fft
.fft_permute(&s
->fft
, (FFTComplex
*)data
);
69 s
->fft
.fft_calc(&s
->fft
, (FFTComplex
*)data
);
71 /* i=0 is a special case because of packing, the DC term is real, so we
72 are going to throw the N/2 term (also real) in with it. */
74 data
[0] = ev
.re
+data
[1];
75 data
[1] = ev
.re
-data
[1];
76 for (i
= 1; i
< (n
>>2); i
++) {
79 /* Separate even and odd FFTs */
80 ev
.re
= k1
*(data
[i1
]+data
[i2
]);
81 od
.im
= -k2
*(data
[i1
]-data
[i2
]);
82 ev
.im
= k1
*(data
[i1
+1]-data
[i2
+1]);
83 od
.re
= k2
*(data
[i1
+1]+data
[i2
+1]);
84 /* Apply twiddle factors to the odd FFT and add to the even FFT */
85 data
[i1
] = ev
.re
+ od
.re
*tcos
[i
] - od
.im
*tsin
[i
];
86 data
[i1
+1] = ev
.im
+ od
.im
*tcos
[i
] + od
.re
*tsin
[i
];
87 data
[i2
] = ev
.re
- od
.re
*tcos
[i
] + od
.im
*tsin
[i
];
88 data
[i2
+1] = -ev
.im
+ od
.im
*tcos
[i
] + od
.re
*tsin
[i
];
90 data
[2*i
+1]=s
->sign_convention
*data
[2*i
+1];
94 s
->fft
.fft_permute(&s
->fft
, (FFTComplex
*)data
);
95 s
->fft
.fft_calc(&s
->fft
, (FFTComplex
*)data
);
99 av_cold
int ff_rdft_init(RDFTContext
*s
, int nbits
, enum RDFTransformType trans
)
104 s
->inverse
= trans
== IDFT_C2R
|| trans
== DFT_C2R
;
105 s
->sign_convention
= trans
== IDFT_R2C
|| trans
== DFT_C2R
? 1 : -1;
107 if (nbits
< 4 || nbits
> 16)
110 if (ff_fft_init(&s
->fft
, nbits
-1, trans
== IDFT_C2R
|| trans
== IDFT_R2C
) < 0)
113 ff_init_ff_cos_tabs(nbits
);
114 s
->tcos
= ff_cos_tabs
[nbits
];
115 s
->tsin
= ff_sin_tabs
[nbits
]+(trans
== DFT_R2C
|| trans
== DFT_C2R
)*(n
>>2);
116 #if !CONFIG_HARDCODED_TABLES
119 const double theta
= (trans
== DFT_R2C
|| trans
== DFT_C2R
? -1 : 1) * 2 * M_PI
/ n
;
120 for (i
= 0; i
< (n
>> 2); i
++)
121 s
->tsin
[i
] = sin(i
* theta
);
124 s
->rdft_calc
= rdft_calc_c
;
126 if (ARCH_ARM
) ff_rdft_init_arm(s
);
131 av_cold
void ff_rdft_end(RDFTContext
*s
)