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comparison libtwamr/pow2.c @ 337:190c4c9a3693

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libtwamr: integrate pow2.c
author Mychaela Falconia <falcon@freecalypso.org>
date Thu, 18 Apr 2024 23:06:59 +0000
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336:7f99b8ed30e5 337:190c4c9a3693
1 /*
2 ********************************************************************************
3 *
4 * GSM AMR-NB speech codec R98 Version 7.6.0 December 12, 2001
5 * R99 Version 3.3.0
6 * REL-4 Version 4.1.0
7 *
8 ********************************************************************************
9 *
10 * File : pow2.c
11 * Purpose : computes L_x = pow(2.0, exponent.fraction)
12 *
13 ********************************************************************************
14 */
15 /*
16 ********************************************************************************
17 * MODULE INCLUDE FILE AND VERSION ID
18 ********************************************************************************
19 */
20 #include "namespace.h"
21 #include "pow2.h"
22
23 /*
24 ********************************************************************************
25 * INCLUDE FILES
26 ********************************************************************************
27 */
28 #include "typedef.h"
29 #include "basic_op.h"
30 #include "no_count.h"
31
32 /*
33 ********************************************************************************
34 * LOCAL VARIABLES AND TABLES
35 ********************************************************************************
36 */
37 #include "pow2.tab" /* Table for Pow2() */
38
39 /*
40 ********************************************************************************
41 * PUBLIC PROGRAM CODE
42 ********************************************************************************
43 */
44 /*************************************************************************
45 *
46 * FUNCTION: Pow2()
47 *
48 * PURPOSE: computes L_x = pow(2.0, exponent.fraction)
49 *
50 * DESCRIPTION:
51 * The function Pow2(L_x) is approximated by a table and linear
52 * interpolation.
53 * 1- i = bit10-b15 of fraction, 0 <= i <= 31
54 * 2- a = bit0-b9 of fraction
55 * 3- L_x = table[i]<<16 - (table[i] - table[i+1]) * a * 2
56 * 4- L_x = L_x >> (30-exponent) (with rounding)
57 *
58 *************************************************************************/
59 Word32 Pow2 ( /* (o) : result (range: 0<=val<=0x7fffffff) */
60 Word16 exponent, /* (i) : Integer part. (range: 0<=val<=30) */
61 Word16 fraction /* (i) : Fractional part. (range: 0.0<=val<1.0) */
62 )
63 {
64 Word16 exp, i, a, tmp;
65 Word32 L_x;
66
67 L_x = L_mult (fraction, 32);/* L_x = fraction<<6 */
68 i = extract_h (L_x); /* Extract b10-b16 of fraction */
69 L_x = L_shr (L_x, 1);
70 a = extract_l (L_x); /* Extract b0-b9 of fraction */
71 a = a & (Word16) 0x7fff; logic16 ();
72
73 L_x = L_deposit_h (table[i]); /* table[i] << 16 */
74 tmp = sub (table[i], table[i + 1]); /* table[i] - table[i+1] */
75 L_x = L_msu (L_x, tmp, a); /* L_x -= tmp*a*2 */
76
77 exp = sub (30, exponent);
78 L_x = L_shr_r (L_x, exp);
79
80 return (L_x);
81 }