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annotate libgsmefr/log2.c @ 585:3c6bf0d26ee7 default tip

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TW-TS-005 reader: fix maximum line length bug TW-TS-005 section 4.1 states: The maximum allowed length of each line is 80 characters, not including the OS-specific newline encoding. The implementation of this line length limit in the TW-TS-005 hex file reader function in the present suite was wrong, such that lines of the full maximum length could not be read. Fix it. Note that this bug affects comment lines too, not just actual RTP payloads. Neither Annex A nor Annex B features an RTP payload format that goes to the maximum of 40 bytes, but if a comment line goes to the maximum allowed length of 80 characters not including the terminating newline, the bug will be triggered, necessitating the present fix.
author Mychaela Falconia <falcon@freecalypso.org>
date Tue, 25 Feb 2025 07:49:28 +0000
parents 68f772469ba7
children
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1 /*************************************************************************
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2 *
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3 * FUNCTION: Log2()
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4 *
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5 * PURPOSE: Computes log2(L_x), where L_x is positive.
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6 * If L_x is negative or zero, the result is 0.
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7 *
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8 * DESCRIPTION:
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9 * The function Log2(L_x) is approximated by a table and linear
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10 * interpolation. The following steps are used to compute Log2(L_x)
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11 *
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12 * 1- Normalization of L_x.
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13 * 2- exponent = 30-exponent
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14 * 3- i = bit25-b31 of L_x; 32<=i<=63 (because of normalization).
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15 * 4- a = bit10-b24
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16 * 5- i -=32
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17 * 6- fraction = table[i]<<16 - (table[i] - table[i+1]) * a * 2
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18 *
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19 *************************************************************************/
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20
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21 #include "gsm_efr.h"
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22 #include "typedef.h"
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23 #include "namespace.h"
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24 #include "basic_op.h"
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25 #include "no_count.h"
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26 #include "sig_proc.h"
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28 #include "log2.tab" /* Table for Log2() */
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30 void Log2 (
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31 Word32 L_x, /* (i) : input value */
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32 Word16 *exponent, /* (o) : Integer part of Log2. (range: 0<=val<=30) */
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33 Word16 *fraction /* (o) : Fractional part of Log2. (range: 0<=val<1) */
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34 )
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35 {
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36 Word16 exp, i, a, tmp;
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37 Word32 L_y;
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39 test ();
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40 if (L_x <= (Word32) 0)
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41 {
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42 *exponent = 0; move16 ();
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43 *fraction = 0; move16 ();
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44 return;
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45 }
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46 exp = norm_l (L_x);
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47 L_x = L_shl (L_x, exp); /* L_x is normalized */
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49 *exponent = sub (30, exp); move16 ();
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51 L_x = L_shr (L_x, 9);
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52 i = extract_h (L_x); /* Extract b25-b31 */
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53 L_x = L_shr (L_x, 1);
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54 a = extract_l (L_x); /* Extract b10-b24 of fraction */
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55 a = a & (Word16) 0x7fff; logic16 ();
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57 i = sub (i, 32);
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59 L_y = L_deposit_h (table[i]); /* table[i] << 16 */
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60 tmp = sub (table[i], table[i + 1]); /* table[i] - table[i+1] */
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61 L_y = L_msu (L_y, tmp, a); /* L_y -= tmp*a*2 */
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63 *fraction = extract_h (L_y);move16 ();
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65 return;
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66 }