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view libtwamr/inv_sqrt.h @ 282:9ee8ad3d4d30

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frtest: rm gsmfr-hand-test and gsmfr-max-out utils These hack programs were never properly documented and were written only as part of a debug chase, in pursuit of a bug that ultimately turned out to be in our then-hacky patch to osmo-bts-sysmo, before beginning of proper patches in Osmocom. These hack programs need to be dropped from the present sw package because they depend on old libgsm, and we are eliminating that dependency.
author Mychaela Falconia <falcon@freecalypso.org>
date Sun, 14 Apr 2024 05:44:47 +0000
parents 54f6bc41ed10
children
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/*
********************************************************************************
*
*      GSM AMR-NB speech codec   R98   Version 7.6.0   December 12, 2001
*                                R99   Version 3.3.0                
*                                REL-4 Version 4.1.0                
*
********************************************************************************
*
*      File             : inv_sqrt.h
*      Purpose          : Computes 1/sqrt(L_x),  where  L_x is positive.
*                       : If L_x is negative or zero, the result is
*                       : 1 (3fff ffff).
*      Description      : The function 1/sqrt(L_x) is approximated by a table 
*                       : and linear interpolation. The inverse square root is 
*                       : computed using the following steps:
*               1- Normalization of L_x.
*               2- If (30-exponent) is even then shift right once.
*               3- exponent = (30-exponent)/2  +1
*               4- i = bit25-b31 of L_x;  16<=i<=63  because of normalization.
*               5- a = bit10-b24
*               6- i -=16
*               7- L_y = table[i]<<16 - (table[i] - table[i+1]) * a * 2
*               8- L_y >>= exponent
*
********************************************************************************
*/
#ifndef inv_sqrt_h
#define inv_sqrt_h "$Id $"
 
/*
********************************************************************************
*                         INCLUDE FILES
********************************************************************************
*/
#include "typedef.h"

/*
********************************************************************************
*                         DEFINITION OF DATA TYPES
********************************************************************************
*/
 
/*
********************************************************************************
*                         DECLARATION OF PROTOTYPES
********************************************************************************
*/
 
Word32 Inv_sqrt (      /* (o) : output value   (range: 0<=val<1)            */
    Word32 L_x           /* (i) : input value    (range: 0<=val<=7fffffff)    */
);
 
#endif