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Diffstat (limited to 'libFDK/include/fft.h')
| -rw-r--r-- | libFDK/include/fft.h | 191 |
1 files changed, 191 insertions, 0 deletions
diff --git a/libFDK/include/fft.h b/libFDK/include/fft.h new file mode 100644 index 0000000..95e7a05 --- /dev/null +++ b/libFDK/include/fft.h @@ -0,0 +1,191 @@ +/*************************** Fraunhofer IIS FDK Tools ********************** + + (C) Copyright Fraunhofer IIS (2001) + All Rights Reserved + + Please be advised that this software and/or program delivery is + Confidential Information of Fraunhofer and subject to and covered by the + + Fraunhofer IIS Software Evaluation Agreement + between Google Inc. and Fraunhofer + effective and in full force since March 1, 2012. + + You may use this software and/or program only under the terms and + conditions described in the above mentioned Fraunhofer IIS Software + Evaluation Agreement. Any other and/or further use requires a separate agreement. + + + $Id$ + Author(s): Josef Hoepfl, DSP Solutions + Description: Fix point FFT + + This software and/or program is protected by copyright law and international + treaties. Any reproduction or distribution of this software and/or program, + or any portion of it, may result in severe civil and criminal penalties, and + will be prosecuted to the maximum extent possible under law. + +******************************************************************************/ + +#ifndef __FFT_H__ +#define __FFT_H__ + +#include "common_fix.h" + +/** + * \brief Perform an inplace complex valued FFT of length 2^n + * + * \param length Length of the FFT to be calculated. + * \param pInput Input/Output data buffer. The input data must have at least 1 bit scale headroom. + * The values are interleaved, real/imag pairs. + * \param scalefactor Pointer to an INT, which contains the current scale of the input data, + * which is updated according to the FFT scale. + */ +void fft(int length, FIXP_DBL *pInput, INT *scalefactor); + +/** + * \brief Perform an inplace complex valued IFFT of length 2^n + * + * \param length Length of the FFT to be calculated. + * \param pInput Input/Output data buffer. The input data must have at least 1 bit scale headroom. + * The values are interleaved, real/imag pairs. + * \param scalefactor Pointer to an INT, which contains the current scale of the input data, + * which is updated according to the IFFT scale. + */ +void ifft(int length, FIXP_DBL *pInput, INT *scalefactor); + + +/* + * Frequently used and fixed short length FFTs. + */ + +LNK_SECTION_CODE_L1 +static void FORCEINLINE fft_4(FIXP_DBL *x) +{ + FIXP_DBL a00, a10, a20, a30, tmp0, tmp1; + + a00 = (x[0] + x[4])>>1; /* Re A + Re B */ + a10 = (x[2] + x[6])>>1; /* Re C + Re D */ + a20 = (x[1] + x[5])>>1; /* Im A + Im B */ + a30 = (x[3] + x[7])>>1; /* Im C + Im D */ + + x[0] = a00 + a10; /* Re A' = Re A + Re B + Re C + Re D */ + x[1] = a20 + a30; /* Im A' = Im A + Im B + Im C + Im D */ + + tmp0 = a00 - x[4]; /* Re A - Re B */ + tmp1 = a20 - x[5]; /* Im A - Im B */ + + x[4] = a00 - a10; /* Re C' = Re A + Re B - Re C - Re D */ + x[5] = a20 - a30; /* Im C' = Im A + Im B - Im C - Im D */ + + a10 = a10 - x[6]; /* Re C - Re D */ + a30 = a30 - x[7]; /* Im C - Im D */ + + x[2] = tmp0 + a30; /* Re B' = Re A - Re B + Im C - Im D */ + x[6] = tmp0 - a30; /* Re D' = Re A - Re B - Im C + Im D */ + x[3] = tmp1 - a10; /* Im B' = Im A - Im B - Re C + Re D */ + x[7] = tmp1 + a10; /* Im D' = Im A - Im B + Re C - Re D */ +} + +LNK_SECTION_CODE_L1 +static void FORCEINLINE fft_8(FIXP_DBL *x) +{ + #define W_PiFOURTH STC(0x5a82799a) + + FIXP_DBL a00, a10, a20, a30; + FIXP_DBL y[16]; + + a00 = (x[0] + x[8])>>1; + a10 = x[4] + x[12]; + a20 = (x[1] + x[9])>>1; + a30 = x[5] + x[13]; + + y[0] = a00 + (a10>>1); + y[4] = a00 - (a10>>1); + y[1] = a20 + (a30>>1); + y[5] = a20 - (a30>>1); + + a00 = a00 - x[8]; + a10 = (a10>>1) - x[12]; + a20 = a20 - x[9]; + a30 = (a30>>1) - x[13]; + + y[2] = a00 + a30; + y[6] = a00 - a30; + y[3] = a20 - a10; + y[7] = a20 + a10; + + a00 = (x[2] + x[10])>>1; + a10 = x[6] + x[14]; + a20 = (x[3] + x[11])>>1; + a30 = x[7] + x[15]; + + y[8] = a00 + (a10>>1); + y[12] = a00 - (a10>>1); + y[9] = a20 + (a30>>1); + y[13] = a20 - (a30>>1); + + a00 = a00 - x[10]; + a10 = (a10>>1) - x[14]; + a20 = a20 - x[11]; + a30 = (a30>>1) - x[15]; + + y[10] = a00 + a30; + y[14] = a00 - a30; + y[11] = a20 - a10; + y[15] = a20 + a10; + + FIXP_DBL vr, vi, ur, ui; + + ur = y[0]>>1; + ui = y[1]>>1; + vr = y[8]; + vi = y[9]; + x[0] = ur + (vr>>1); + x[1] = ui + (vi>>1); + x[8] = ur - (vr>>1); + x[9] = ui - (vi>>1); + + ur = y[4]>>1; + ui = y[5]>>1; + vi = y[12]; + vr = y[13]; + x[4] = ur + (vr>>1); + x[5] = ui - (vi>>1); + x[12] = ur - (vr>>1); + x[13] = ui + (vi>>1); + + ur = y[10]; + ui = y[11]; + vr = fMultDiv2(ui+ur,W_PiFOURTH); + vi = fMultDiv2(ui-ur,W_PiFOURTH); + ur = y[2]; + ui = y[3]; + x[2] = (ur>>1) + vr; + x[3] = (ui>>1) + vi; + x[10] = (ur>>1) - vr; + x[11] = (ui>>1) - vi; + + ur = y[14]; + ui = y[15]; + vr = fMultDiv2(ui-ur,W_PiFOURTH); + vi = fMultDiv2(ui+ur,W_PiFOURTH); + ur = y[6]; + ui = y[7]; + x[6] = (ur>>1) + vr; + x[7] = (ui>>1) - vi; + x[14] = (ur>>1) - vr; + x[15] = (ui>>1) + vi; +} + +/** + * \brief FFT of fixed length 16 + */ +inline void fft_16(FIXP_DBL *x); + +/** + * \brief FFT of fixed length 32 + */ +inline void fft_32(FIXP_DBL *x); + + +#endif |