log2.cpp

实现3GPP的GSM中AMR语音的CODECS。

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/****************************************************************************************
Portions of this file are derived from the following 3GPP standard:

    3GPP TS 26.073
    ANSI-C code for the Adaptive Multi-Rate (AMR) speech codec
    Available from http://www.3gpp.org

(C) 2004, 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TTA, TTC)
Permission to distribute, modify and use this file under the standard license
terms listed above has been obtained from the copyright holder.
****************************************************************************************/
/*




 Filename: /audio/gsm_amr/c/src/log2.c

     Date: 09/22/2000

------------------------------------------------------------------------------
 REVISION HISTORY

 Description: Updated template used to PV coding template. Moved Log2_norm
	      function to its own file.

 Description: Changed l_shl.c to l_shl.h in Include section.

 Description: Updated template. Changed function interface to pass in a
              pointer to overflow flag into the function instead of using a
              global flag. Changed input pointer names for clarity.

 Description:
              1. Eliminated l_shl function knowing that after normalization
                 the left shift factor will not saturate.
              2. Eliminated unused include files typedef.h and l_shl.h.


 Description:

------------------------------------------------------------------------------
*/

/*----------------------------------------------------------------------------
; INCLUDES
----------------------------------------------------------------------------*/
#include "log2.h"
#include "basic_op.h"
#include "log2_norm.h"

/*----------------------------------------------------------------------------
; MACROS
; [Define module specific macros here]
----------------------------------------------------------------------------*/

/*----------------------------------------------------------------------------
; DEFINES
; [Include all pre-processor statements here. Include conditional
; compile variables also.]
----------------------------------------------------------------------------*/

/*----------------------------------------------------------------------------
; LOCAL FUNCTION DEFINITIONS
; [List function prototypes here]
----------------------------------------------------------------------------*/

/*----------------------------------------------------------------------------
; LOCAL VARIABLE DEFINITIONS
; [Variable declaration - defined here and used outside this module]
----------------------------------------------------------------------------*/


/*
------------------------------------------------------------------------------
 FUNCTION NAME: log2()
------------------------------------------------------------------------------
 INPUT AND OUTPUT DEFINITIONS

 Inputs:
	L_x = input value of type Word32
	pExponent = pointer to the integer part of Log2 of type Word16 whose
		   valid range is: 0 <= value <= 30
	pFraction = pointer to the fractional part of Log2 of type Word16
		   whose valid range is: 0 <= value < 1
    pOverflow = pointer to overflow flag


 Outputs:
	pExponent -> integer part of the newly calculated Log2
	pFraction -> fractional part of the newly calculated Log2
	pOverflow -> 1 if the log2() operation resulted in saturation

 Returns:
    None

 Global Variables Used:
    None

 Local Variables Needed:
    None

------------------------------------------------------------------------------
 FUNCTION DESCRIPTION

 This function computes logarithm (base2) of the input L_x, where L_x is
 positive. If L_x is negative or zero, the result is 0.

 This function first normalizes the input L_x and calls the function Log2_norm
 to calculate the logarithm.

------------------------------------------------------------------------------
 REQUIREMENTS

 None

------------------------------------------------------------------------------
 REFERENCES

 [1] log2.c,  UMTS GSM AMR speech codec, R99 - Version 3.2.0, March 2, 2001

------------------------------------------------------------------------------
 PSEUDO-CODE


------------------------------------------------------------------------------
 RESOURCES USED [optional]

 When the code is written for a specific target processor the
 the resources used should be documented below.

 HEAP MEMORY USED: x bytes

 STACK MEMORY USED: x bytes

 CLOCK CYCLES: (cycle count equation for this function) + (variable
                used to represent cycle count for each subroutine
                called)
     where: (cycle count variable) = cycle count for [subroutine
                                     name]

------------------------------------------------------------------------------
 CAUTION [optional]
 [State any special notes, constraints or cautions for users of this function]

------------------------------------------------------------------------------
*/

/*----------------------------------------------------------------------------
; FUNCTION CODE
----------------------------------------------------------------------------*/
void Log2(
    Word32 L_x,         /* (i) : input value                                */
    Word16 *pExponent,  /* (o) : Integer part of Log2.   (range: 0<=val<=30)*/
    Word16 *pFraction,  /* (o) : Fractional part of Log2. (range: 0<=val<1) */
    Flag   *pOverflow   /* (i/o) : overflow flag                            */
)
{
    Word16 exp;
    Word32 result;
    OSCL_UNUSED_ARG(pOverflow);

    exp = norm_l(L_x);
    result = L_x << exp;
    Log2_norm(result, exp, pExponent, pFraction);

    return;
}