303 lines
13 KiB
C
303 lines
13 KiB
C
/* fft.c - Fixed-point Fast Fourier Transform */
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/*
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fix_fft() perform FFT or inverse FFT
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fix_mpy() perform fixed-point multiplication.
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Sinewave[1024] sinewave normalized to 32767 (= 1.0).
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All data are fixed-point short integers, in which
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-32768 to +32768 represent -1.0 to +1.0. Integer arithmetic
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is used for speed, instead of the more natural floating-point.
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For the forward FFT (time -> freq), fixed scaling is
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performed to prevent arithmetic overflow, and to map a 0dB
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sine/cosine wave (i.e. amplitude = 32767) to two -6dB freq
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coefficients; the one in the lower half is reported as 0dB.
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For the inverse FFT (freq -> time), fixed scaling cannot be
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done, as two 0dB coefficients would sum to a peak amplitude of
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64K, overflowing the 32k range of the fixed-point integers.
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Thus, the fix_fft() routine performs variable scaling, and
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returns a value which is the number of bits LEFT by which
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the output must be shifted to get the actual amplitude
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(i.e. if fix_fft() returns 3, each value of fr[] and fi[]
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must be multiplied by 8 (2^3) for proper scaling.
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Clearly, this cannot be done within the fixed-point short
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integers. In practice, if the result is to be used as a
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filter, the scale_shift can usually be ignored, as the
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result will be approximately correctly normalized as is.
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Source Code taken by http://www.jjj.de/crs4: integer_fft.c
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Last Modified by Sebastian Haas at Oct. 2014.
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*/
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#include "fft-org.h"
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/*
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* fix_fft() - perform fast Fourier transform.
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*
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* if n>0 FFT is done, if n<0 inverse FFT is done
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* fr[n],fi[n] are real,imaginary arrays, INPUT AND RESULT.
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* size of data = 2^m
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* set inverse to 0=dft, 1=idft
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*/
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int fix_fft_org(fixed fr[], fixed fi[], int m, int inverse)
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{
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int mr,nn,i,j,l,k,istep, n, scale, shift;
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fixed qr,qi; //even input
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fixed tr,ti; //odd input
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fixed wr,wi; //twiddle factor
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//number of input data
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n = 1<<m;
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if(n > N_WAVE) return -1;
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mr = 0;
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nn = n - 1;
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scale = 0;
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/* decimation in time - re-order data */
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for(m=1; m<=nn; ++m) {
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l = n;
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do{
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l >>= 1;
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}while(mr+l > nn);
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mr = (mr & (l-1)) + l;
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if(mr <= m) continue;
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tr = fr[m];
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fr[m] = fr[mr];
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fr[mr] = tr;
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ti = fi[m];
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fi[m] = fi[mr];
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fi[mr] = ti;
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}
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l = 1;
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k = LOG2_N_WAVE-1;
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while(l < n)
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{
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if(inverse)
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{
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/* variable scaling, depending upon data */
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shift = 0;
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for(i=0; i<n; ++i)
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{
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j = fr[i];
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if(j < 0) j = -j;
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m = fi[i];
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if(m < 0) m = -m;
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if(j > 16383 || m > 16383)
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{
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shift = 1;
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break;
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}
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}
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if(shift) ++scale;
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}
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else
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{
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/* fixed scaling, for proper normalization -
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there will be log2(n) passes, so this
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results in an overall factor of 1/n,
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distributed to maximize arithmetic accuracy. */
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shift = 1;
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}
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/* it may not be obvious, but the shift will be performed
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on each data point exactly once, during this pass. */
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istep = l << 1; //step width of current butterfly
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for(m=0; m<l; ++m)
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{
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j = m << k;
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/* 0 <= j < N_WAVE/2 */
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wr = Sinewave_org[j+N_WAVE/4];
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wi = -Sinewave_org[j];
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if(inverse) wi = -wi;
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if(shift)
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{
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wr >>= 1;
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wi >>= 1;
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}
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for(i=m; i<n; i+=istep)
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{
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j = i + l;
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tr = fix_mpy_org(wr,fr[j]) - fix_mpy_org(wi,fi[j]);
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ti = fix_mpy_org(wr,fi[j]) + fix_mpy_org(wi,fr[j]);
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qr = fr[i];
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qi = fi[i];
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if(shift)
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{
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qr >>= 1;
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qi >>= 1;
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}
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fr[j] = qr - tr;
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fi[j] = qi - ti;
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fr[i] = qr + tr;
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fi[i] = qi + ti;
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}
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}
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--k;
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l = istep;
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}
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return scale;
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}
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/*
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fix_mpy() - fixed-point multiplication
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*/
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fixed fix_mpy_org(fixed a, fixed b)
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{
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FIX_MPY(a,a,b);
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return a;
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}
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fixed Sinewave_org[1024] = {
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0, 201, 402, 603, 804, 1005, 1206, 1406,
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1607, 1808, 2009, 2209, 2410, 2610, 2811, 3011,
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3211, 3411, 3611, 3811, 4011, 4210, 4409, 4608,
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4807, 5006, 5205, 5403, 5601, 5799, 5997, 6195,
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6392, 6589, 6786, 6982, 7179, 7375, 7571, 7766,
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7961, 8156, 8351, 8545, 8739, 8932, 9126, 9319,
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9511, 9703, 9895, 10087, 10278, 10469, 10659, 10849,
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11038, 11227, 11416, 11604, 11792, 11980, 12166, 12353,
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12539, 12724, 12909, 13094, 13278, 13462, 13645, 13827,
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14009, 14191, 14372, 14552, 14732, 14911, 15090, 15268,
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15446, 15623, 15799, 15975, 16150, 16325, 16499, 16672,
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16845, 17017, 17189, 17360, 17530, 17699, 17868, 18036,
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18204, 18371, 18537, 18702, 18867, 19031, 19194, 19357,
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19519, 19680, 19840, 20000, 20159, 20317, 20474, 20631,
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20787, 20942, 21096, 21249, 21402, 21554, 21705, 21855,
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22004, 22153, 22301, 22448, 22594, 22739, 22883, 23027,
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23169, 23311, 23452, 23592, 23731, 23869, 24006, 24143,
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24278, 24413, 24546, 24679, 24811, 24942, 25072, 25201,
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25329, 25456, 25582, 25707, 25831, 25954, 26077, 26198,
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26318, 26437, 26556, 26673, 26789, 26905, 27019, 27132,
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27244, 27355, 27466, 27575, 27683, 27790, 27896, 28001,
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28105, 28208, 28309, 28410, 28510, 28608, 28706, 28802,
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28897, 28992, 29085, 29177, 29268, 29358, 29446, 29534,
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29621, 29706, 29790, 29873, 29955, 30036, 30116, 30195,
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30272, 30349, 30424, 30498, 30571, 30643, 30713, 30783,
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30851, 30918, 30984, 31049,
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31113, 31175, 31236, 31297,
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31356, 31413, 31470, 31525, 31580, 31633, 31684, 31735,
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31785, 31833, 31880, 31926, 31970, 32014, 32056, 32097,
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32137, 32176, 32213, 32249, 32284, 32318, 32350, 32382,
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32412, 32441, 32468, 32495, 32520, 32544, 32567, 32588,
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32609, 32628, 32646, 32662, 32678, 32692, 32705, 32717,
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32727, 32736, 32744, 32751, 32757, 32761, 32764, 32766,
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32767, 32766, 32764, 32761, 32757, 32751, 32744, 32736,
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32727, 32717, 32705, 32692, 32678, 32662, 32646, 32628,
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32609, 32588, 32567, 32544, 32520, 32495, 32468, 32441,
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32412, 32382, 32350, 32318, 32284, 32249, 32213, 32176,
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32137, 32097, 32056, 32014, 31970, 31926, 31880, 31833,
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31785, 31735, 31684, 31633, 31580, 31525, 31470, 31413,
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31356, 31297, 31236, 31175, 31113, 31049, 30984, 30918,
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30851, 30783, 30713, 30643, 30571, 30498, 30424, 30349,
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30272, 30195, 30116, 30036, 29955, 29873, 29790, 29706,
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29621, 29534, 29446, 29358, 29268, 29177, 29085, 28992,
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28897, 28802, 28706, 28608, 28510, 28410, 28309, 28208,
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28105, 28001, 27896, 27790, 27683, 27575, 27466, 27355,
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27244, 27132, 27019, 26905, 26789, 26673, 26556, 26437,
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26318, 26198, 26077, 25954, 25831, 25707, 25582, 25456,
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25329, 25201, 25072, 24942, 24811, 24679, 24546, 24413,
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24278, 24143, 24006, 23869, 23731, 23592, 23452, 23311,
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23169, 23027, 22883, 22739, 22594, 22448, 22301, 22153,
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22004, 21855, 21705, 21554, 21402, 21249, 21096, 20942,
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20787, 20631, 20474, 20317, 20159, 20000, 19840, 19680,
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19519, 19357, 19194, 19031, 18867, 18702, 18537, 18371,
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18204, 18036, 17868, 17699, 17530, 17360, 17189, 17017,
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16845, 16672, 16499, 16325, 16150, 15975, 15799, 15623,
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15446, 15268, 15090, 14911, 14732, 14552, 14372, 14191,
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14009, 13827, 13645, 13462, 13278, 13094, 12909, 12724,
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12539, 12353, 12166, 11980, 11792, 11604, 11416, 11227,
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11038, 10849, 10659, 10469, 10278, 10087, 9895, 9703,
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9511, 9319, 9126, 8932, 8739, 8545, 8351, 8156,
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7961, 7766, 7571, 7375, 7179, 6982, 6786, 6589,
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6392, 6195, 5997, 5799, 5601, 5403, 5205, 5006,
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4807, 4608, 4409, 4210, 4011, 3811, 3611, 3411,
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3211, 3011, 2811, 2610, 2410, 2209, 2009, 1808,
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1607, 1406, 1206, 1005, 804, 603, 402, 201,
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0, -201, -402, -603, -804, -1005, -1206, -1406,
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-1607, -1808, -2009, -2209, -2410, -2610, -2811, -3011,
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-3211, -3411, -3611, -3811, -4011, -4210, -4409, -4608,
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-4807, -5006, -5205, -5403, -5601, -5799, -5997, -6195,
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-6392, -6589, -6786, -6982, -7179, -7375, -7571, -7766,
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-7961, -8156, -8351, -8545, -8739, -8932, -9126, -9319,
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-9511, -9703, -9895, -10087, -10278, -10469, -10659, -10849,
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-11038, -11227, -11416, -11604, -11792, -11980, -12166, -12353,
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-12539, -12724, -12909, -13094, -13278, -13462, -13645, -13827,
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-14009, -14191, -14372, -14552, -14732, -14911, -15090, -15268,
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-15446, -15623, -15799, -15975, -16150, -16325, -16499, -16672,
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-16845, -17017, -17189, -17360, -17530, -17699, -17868, -18036,
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-18204, -18371, -18537, -18702, -18867, -19031, -19194, -19357,
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-19519, -19680, -19840, -20000, -20159, -20317, -20474, -20631,
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-20787, -20942, -21096, -21249, -21402, -21554, -21705, -21855,
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-22004, -22153, -22301, -22448, -22594, -22739, -22883, -23027,
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-23169, -23311, -23452, -23592, -23731, -23869, -24006, -24143,
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-24278, -24413, -24546, -24679, -24811, -24942, -25072, -25201,
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-25329, -25456, -25582, -25707, -25831, -25954, -26077, -26198,
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-26318, -26437, -26556, -26673, -26789, -26905, -27019, -27132,
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-27244, -27355, -27466, -27575, -27683, -27790, -27896, -28001,
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-28105, -28208, -28309, -28410, -28510, -28608, -28706, -28802,
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-28897, -28992, -29085, -29177, -29268, -29358, -29446, -29534,
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-29621, -29706, -29790, -29873, -29955, -30036, -30116, -30195,
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-30272, -30349, -30424, -30498, -30571, -30643, -30713, -30783,
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-30851, -30918, -30984, -31049, -31113, -31175, -31236, -31297,
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-31356, -31413, -31470, -31525, -31580, -31633, -31684, -31735,
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-31785, -31833, -31880, -31926, -31970, -32014, -32056, -32097,
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-32137, -32176, -32213, -32249, -32284, -32318, -32350, -32382,
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-32412, -32441, -32468, -32495, -32520, -32544, -32567, -32588,
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-32609, -32628, -32646, -32662, -32678, -32692, -32705, -32717,
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-32727, -32736, -32744, -32751, -32757, -32761, -32764, -32766,
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-32767, -32766, -32764, -32761, -32757, -32751, -32744, -32736,
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-32727, -32717, -32705, -32692, -32678, -32662, -32646, -32628,
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-32609, -32588, -32567, -32544, -32520, -32495, -32468, -32441,
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-32412, -32382, -32350, -32318, -32284, -32249, -32213, -32176,
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-32137, -32097, -32056, -32014, -31970, -31926, -31880, -31833,
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-31785, -31735, -31684, -31633, -31580, -31525, -31470, -31413,
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-31356, -31297, -31236, -31175, -31113, -31049, -30984, -30918,
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-30851, -30783, -30713, -30643, -30571, -30498, -30424, -30349,
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-30272, -30195, -30116, -30036, -29955, -29873, -29790, -29706,
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-29621, -29534, -29446, -29358, -29268, -29177, -29085, -28992,
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-28897, -28802, -28706, -28608, -28510, -28410, -28309, -28208,
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-28105, -28001, -27896, -27790, -27683, -27575, -27466, -27355,
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-27244, -27132, -27019, -26905, -26789, -26673, -26556, -26437,
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-26318, -26198, -26077, -25954, -25831, -25707, -25582, -25456,
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-25329, -25201, -25072, -24942, -24811, -24679, -24546, -24413,
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-24278, -24143, -24006, -23869, -23731, -23592, -23452, -23311,
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-23169, -23027, -22883, -22739, -22594, -22448, -22301, -22153,
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-22004, -21855, -21705, -21554, -21402, -21249, -21096, -20942,
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-20787, -20631, -20474, -20317, -20159, -20000, -19840, -19680,
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-19519, -19357, -19194, -19031, -18867, -18702, -18537, -18371,
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-18204, -18036, -17868, -17699, -17530, -17360, -17189, -17017,
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-16845, -16672, -16499, -16325, -16150, -15975, -15799, -15623,
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-15446, -15268, -15090, -14911, -14732, -14552, -14372, -14191,
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-14009, -13827, -13645, -13462, -13278, -13094, -12909, -12724,
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-12539, -12353, -12166, -11980, -11792, -11604, -11416, -11227,
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-11038, -10849, -10659, -10469, -10278, -10087, -9895, -9703,
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-9511, -9319, -9126, -8932, -8739, -8545, -8351, -8156,
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-7961, -7766, -7571, -7375, -7179, -6982, -6786, -6589,
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-6392, -6195, -5997, -5799, -5601, -5403, -5205, -5006,
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-4807, -4608, -4409, -4210, -4011, -3811, -3611, -3411,
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-3211, -3011, -2811, -2610, -2410, -2209, -2009, -1808,
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-1607, -1406, -1206, -1005, -804, -603, -402, -201,
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};
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