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Diffstat (limited to 'media/libstagefright/codecs/aacdec/mdct_fxp.cpp')
| -rw-r--r-- | media/libstagefright/codecs/aacdec/mdct_fxp.cpp | 450 |
1 files changed, 450 insertions, 0 deletions
diff --git a/media/libstagefright/codecs/aacdec/mdct_fxp.cpp b/media/libstagefright/codecs/aacdec/mdct_fxp.cpp new file mode 100644 index 0000000..df371e8 --- /dev/null +++ b/media/libstagefright/codecs/aacdec/mdct_fxp.cpp @@ -0,0 +1,450 @@ +/* ------------------------------------------------------------------ + * Copyright (C) 1998-2009 PacketVideo + * + * Licensed under the Apache License, Version 2.0 (the "License"); + * you may not use this file except in compliance with the License. + * You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either + * express or implied. + * See the License for the specific language governing permissions + * and limitations under the License. + * ------------------------------------------------------------------- + */ +/* + + Pathname: mdct_fxp.c + Funtions: fft_rx2 + +------------------------------------------------------------------------------ + INPUT AND OUTPUT DEFINITIONS + + Inputs: + data_quant = Input vector, with quantized Q15 spectral lines: + type Int32 + + Q_FFTarray = Scratch memory used for in-place IFFT calculation, + min size required 1024, type Int32 + + n = Length of input vector "data_quant". Currently 256 or 2048. + type const Int + + Local Stores/Buffers/Pointers Needed: + None + + Global Stores/Buffers/Pointers Needed: + None + + Outputs: + shift = shift factor to reflect scaling introduced by FFT and mdct_fxp, + + Pointers and Buffers Modified: + calculation are done in-place and returned in "data_quant" + + Local Stores Modified: + None + + Global Stores Modified: + None + +------------------------------------------------------------------------------ + FUNCTION DESCRIPTION + + The MDCT is a linear orthogonal lapped transform, based on the idea of + time domain aliasing cancellation (TDAC). + MDCT is critically sampled, which means that though it is 50% overlapped, + a sequence data after MDCT has the same number of coefficients as samples + before the transform (after overlap-and-add). This means, that a single + block of MDCT data does not correspond to the original block on which the + MDCT was performed. When subsequent blocks of data are added (still using + 50% overlap), the errors introduced by the transform cancels out. + Thanks to the overlapping feature, the MDCT is very useful for + quantization. It effectively removes the otherwise easily detectable + blocking artifact between transform blocks. + N = length of input vector X + X = vector of length N/2, will hold fixed point DCT + k = 0:1:N-1 + + N-1 + X(m) = 2 SUM x(k)*cos(pi/(2*N)*(2*k+1+N/2)*(2*m+1)) + k=0 + + + The window that completes the TDAC is applied before calling this function. + The MDCT can be calculated using an FFT, for this, the MDCT needs to be + rewritten as an odd-time odd-frequency discrete Fourier transform. Thus, + the MDCT can be calculated using only one n/4 point FFT and some pre and + post-rotation of the sample points. + + Computation of the MDCT implies computing + + x = ( y - y ) + j( y + y ) + n 2n N/2-1-2n N-1-2n N/2+2n + + using the Fast discrete cosine transform as described in [2] + + where x(n) is an input with N points + + x(n) ---------------------------- + | + | + Pre-rotation by exp(j(2pi/N)(n+1/8)) + | + | + N/4- point FFT + | + | + Post-rotation by exp(j(2pi/N)(k+1/8)) + | + | + ------------- DCT + + By considering the N/2 overlap, a relation between successive input blocks + is found: + + x (2n) = x (N/2 + 2n) + m+1 m +------------------------------------------------------------------------------ + REQUIREMENTS + + This function should provide a fixed point MDCT with an average + quantization error less than 1 %. + +------------------------------------------------------------------------------ + REFERENCES + + [1] Analysis/Synthesis Filter Bank design based on time domain + aliasing cancellation + Jhon Princen, et. al. + IEEE Transactions on ASSP, vol ASSP-34, No. 5 October 1986 + Pg 1153 - 1161 + + [2] Regular FFT-related transform kernels for DCT/DST based + polyphase filterbanks + Rolf Gluth + Proc. ICASSP 1991, pg. 2205 - 2208 + +------------------------------------------------------------------------------ + PSEUDO-CODE + + Cx, Cy are complex number + + + exp = log2(n)-1 + + FOR ( k=0; k< n/4; k +=2) + + Cx = (data_quant[3n/4 + k] + data_quant[3n/4 - 1 - k]) + + j (data_quant[ n/4 + k] - data_quant[ n/4 - 1 - k]) + + Q_FFTarray = Cx * exp(-j(2pi/n)(k+1/8)) + + ENDFOR + + FOR ( k=n/4; k< n/2; k +=2) + + Cx = (data_quant[3n/4 - 1 - k] + data_quant[ - n/4 + k]) + + j (data_quant[5n/4 - 1 - k] - data_quant[ n/4 + k]) + + Q_FFTarray = Cx * exp(-j(2pi/n)(k+1/8)) + + ENDFOR + + CALL FFT( Q_FFTarray, n/4) + + MODIFYING( Q_FFTarray ) + + RETURNING( shift ) + + FOR ( k=0; k< n/2; k +=2) + + Cx = Q_FFTarray[ k] + j Q_FFTarray[ k+1] + + Cy = 2 * Cx * exp(-j(2pi/n)(k+1/8)) + + data_quant[ k ] = - Real(Cy) + data_quant[ n/2 - 1 - k ] = Imag(Cy) + data_quant[ n/2 + k ] = - Imag(Cy) + data_quant[ n - k ] = Real(Cy) + + ENDFOR + + MODIFIED data_quant[] + + RETURN (-shift-1) + +------------------------------------------------------------------------------ + RESOURCES USED + When the code is written for a specific target processor the + the resources used should be documented below. + + STACK USAGE: [stack count for this module] + [variable to represent + stack usage for each subroutine called] + + where: [stack usage variable] = stack usage for [subroutine + name] (see [filename].ext) + + DATA MEMORY USED: x words + + PROGRAM MEMORY USED: x words + + CLOCK CYCLES: [cycle count equation for this module] + [variable + used to represent cycle count for each subroutine + called] + + where: [cycle count variable] = cycle count for [subroutine + name] (see [filename].ext) + +------------------------------------------------------------------------------ +*/ + + +/*---------------------------------------------------------------------------- +; INCLUDES +----------------------------------------------------------------------------*/ + +#include "pv_audio_type_defs.h" +#include "mdct_fxp.h" +#include "fft_rx4.h" +#include "mix_radix_fft.h" +#include "fwd_long_complex_rot.h" +#include "fwd_short_complex_rot.h" + + +/*---------------------------------------------------------------------------- +; MACROS +; Define module specific macros here +----------------------------------------------------------------------------*/ + +/*---------------------------------------------------------------------------- +; DEFINES +; Include all pre-processor statements here. Include conditional +; compile variables also. +----------------------------------------------------------------------------*/ +#define ERROR_IN_FRAME_SIZE 10 + + +/*---------------------------------------------------------------------------- +; LOCAL FUNCTION DEFINITIONS +; Function Prototype declaration +----------------------------------------------------------------------------*/ + +/*---------------------------------------------------------------------------- +; LOCAL VARIABLE DEFINITIONS +; Variable declaration - defined here and used outside this module +----------------------------------------------------------------------------*/ + + +/*---------------------------------------------------------------------------- +; EXTERNAL FUNCTION REFERENCES +; Declare functions defined elsewhere and referenced in this module +----------------------------------------------------------------------------*/ + +/*---------------------------------------------------------------------------- +; EXTERNAL VARIABLES REFERENCES +; Declare variables used in this module but defined elsewhere +----------------------------------------------------------------------------*/ + +/*---------------------------------------------------------------------------- +; EXTERNAL GLOBAL STORE/BUFFER/POINTER REFERENCES +; Declare variables used in this module but defined elsewhere +----------------------------------------------------------------------------*/ + + +/*---------------------------------------------------------------------------- +; FUNCTION CODE +----------------------------------------------------------------------------*/ + + +Int mdct_fxp( + Int32 data_quant[], + Int32 Q_FFTarray[], + Int n) +{ + + Int32 temp_re; + Int32 temp_im; + + Int32 temp_re_32; + Int32 temp_im_32; + + Int16 cos_n; + Int16 sin_n; + Int32 exp_jw; + Int shift; + + + const Int32 *p_rotate; + + + Int32 *p_data_1; + Int32 *p_data_2; + Int32 *p_data_3; + Int32 *p_data_4; + + Int32 *p_Q_FFTarray; + + Int32 max1; + + Int k; + Int n_2 = n >> 1; + Int n_4 = n >> 2; + Int n_8 = n >> 3; + Int n_3_4 = 3 * n_4; + + switch (n) + { + case SHORT_WINDOW_TYPE: + p_rotate = (Int32 *)exp_rotation_N_256; + break; + + case LONG_WINDOW_TYPE: + p_rotate = (Int32 *)exp_rotation_N_2048; + break; + + default: + /* + * There is no defined behavior for a non supported frame + * size. By returning a fixed scaling factor, the input will + * scaled down and this will be heard as a low level noise + */ + return(ERROR_IN_FRAME_SIZE); + + } + + /*--- Reordering and Pre-rotation by exp(-j(2pi/N)(r+1/8)) */ + p_data_1 = &data_quant[n_3_4]; + p_data_2 = &data_quant[n_3_4 - 1]; + p_data_3 = &data_quant[n_4]; + p_data_4 = &data_quant[n_4 - 1]; + + p_Q_FFTarray = Q_FFTarray; + + max1 = 0; + + for (k = n_8; k > 0; k--) + { + /* + * scale down to ensure numbers are Q15 + * temp_re and temp_im are 32-bit but + * only the lower 16 bits are used + */ + + temp_re = (*(p_data_1++) + *(p_data_2--)) >> 1; + temp_im = (*(p_data_3++) - *(p_data_4--)) >> 1; + + + /* + * cos_n + j*sin_n == exp(j(2pi/N)(k+1/8)) + */ + + exp_jw = *p_rotate++; + + cos_n = (Int16)(exp_jw >> 16); + sin_n = (Int16)(exp_jw & 0xFFFF); + + temp_re_32 = temp_re * cos_n + temp_im * sin_n; + temp_im_32 = temp_im * cos_n - temp_re * sin_n; + *(p_Q_FFTarray++) = temp_re_32; + *(p_Q_FFTarray++) = temp_im_32; + max1 |= (temp_re_32 >> 31) ^ temp_re_32; + max1 |= (temp_im_32 >> 31) ^ temp_im_32; + + + p_data_1++; + p_data_2--; + p_data_4--; + p_data_3++; + } + + + p_data_1 = &data_quant[n - 1]; + p_data_2 = &data_quant[n_2 - 1]; + p_data_3 = &data_quant[n_2]; + p_data_4 = data_quant; + + for (k = n_8; k > 0; k--) + { + /* + * scale down to ensure numbers are Q15 + */ + temp_re = (*(p_data_2--) - *(p_data_4++)) >> 1; + temp_im = (*(p_data_1--) + *(p_data_3++)) >> 1; + + p_data_2--; + p_data_1--; + p_data_4++; + p_data_3++; + + /* + * cos_n + j*sin_n == exp(j(2pi/N)(k+1/8)) + */ + + exp_jw = *p_rotate++; + + cos_n = (Int16)(exp_jw >> 16); + sin_n = (Int16)(exp_jw & 0xFFFF); + + temp_re_32 = temp_re * cos_n + temp_im * sin_n; + temp_im_32 = temp_im * cos_n - temp_re * sin_n; + + *(p_Q_FFTarray++) = temp_re_32; + *(p_Q_FFTarray++) = temp_im_32; + max1 |= (temp_re_32 >> 31) ^ temp_re_32; + max1 |= (temp_im_32 >> 31) ^ temp_im_32; + + + } /* for(k) */ + + + + p_Q_FFTarray = Q_FFTarray; + + if (max1) + { + + if (n != SHORT_WINDOW_TYPE) + { + + shift = mix_radix_fft( + Q_FFTarray, + &max1); + + shift += fwd_long_complex_rot( + Q_FFTarray, + data_quant, + max1); + + } + else /* n_4 is 64 */ + { + + shift = fft_rx4_short( + Q_FFTarray, + &max1); + + shift += fwd_short_complex_rot( + Q_FFTarray, + data_quant, + max1); + } + + } + else + { + shift = -31; + } + + /* + * returns shift introduced by FFT and mdct_fxp, 12 accounts for + * regular downshift (14) and MDCT scale factor (-2) + * number are returned as 16 bits + */ + return (12 - shift); + +} /* mdct_fxp */ + |