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annotate libgsmefr/pow2.c @ 183:452c1d5a6268

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libgsmefr BFI w/o data: emit zero output after decoder reset In real-life usage, each EFR decoder session will most likely begin with lots of BFI frames before the first real frame arrives. However, because the spec-defined home state of the decoder is speech rather than CN, our regular logic for BFI w/o data would have to feed pseudorandom noise to the decoder (in the "fixed codebook excitation pulses" part), which is silly to do at the beginning of the decoder session right out of reset. Therefore, let's check reset_flag_old, and if we are still in the reset state, simply emit zero output.
author Mychaela Falconia <falcon@freecalypso.org>
date Tue, 03 Jan 2023 00:12:18 +0000
parents 33714b36841a
children
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1 /*************************************************************************
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2 *
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3 * FUNCTION: Pow2()
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4 *
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5 * PURPOSE: computes L_x = pow(2.0, exponent.fraction)
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6 *
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7 * DESCRIPTION:
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8 * The function Pow2(L_x) is approximated by a table and linear
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9 * interpolation.
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10 * 1- i = bit10-b15 of fraction, 0 <= i <= 31
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11 * 2- a = bit0-b9 of fraction
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12 * 3- L_x = table[i]<<16 - (table[i] - table[i+1]) * a * 2
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13 * 4- L_x = L_x >> (30-exponent) (with rounding)
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14 *
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15 *************************************************************************/
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16
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17 #include "gsm_efr.h"
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18 #include "typedef.h"
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19 #include "namespace.h"
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20 #include "basic_op.h"
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21 #include "no_count.h"
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22 #include "sig_proc.h"
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24 #include "pow2.tab" /* Table for Pow2() */
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26 Word32 Pow2 ( /* (o) : result (range: 0<=val<=0x7fffffff) */
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27 Word16 exponent, /* (i) : Integer part. (range: 0<=val<=30) */
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28 Word16 fraction /* (i) : Fractional part. (range: 0.0<=val<1.0) */
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29 )
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30 {
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31 Word16 exp, i, a, tmp;
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32 Word32 L_x;
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34 L_x = L_mult (fraction, 32);/* L_x = fraction<<6 */
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35 i = extract_h (L_x); /* Extract b10-b16 of fraction */
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36 L_x = L_shr (L_x, 1);
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37 a = extract_l (L_x); /* Extract b0-b9 of fraction */
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38 a = a & (Word16) 0x7fff; logic16 ();
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40 L_x = L_deposit_h (table[i]); /* table[i] << 16 */
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41 tmp = sub (table[i], table[i + 1]); /* table[i] - table[i+1] */
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42 L_x = L_msu (L_x, tmp, a); /* L_x -= tmp*a*2 */
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44 exp = sub (30, exponent);
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45 L_x = L_shr_r (L_x, exp);
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47 return (L_x);
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48 }