FreeCalypso > hg > gsm-codec-lib
annotate libgsmefr/pow2.c @ 187:6ad363f7ea30
libgsmefr/d1035pf.c: perf opt
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Tue, 03 Jan 2023 03:22:04 +0000 |
parents | 33714b36841a |
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rev | line source |
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libgsmefr: import most *.c files from ETSI source
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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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23 |
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24 #include "pow2.tab" /* Table for Pow2() */ |
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25 |
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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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33 |
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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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39 |
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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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43 |
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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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46 |
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47 return (L_x); |
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48 } |