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/* ------------------------------------------------------------------
* Copyright (C) 1998-2009 PacketVideo
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
* express or implied.
* See the License for the specific language governing permissions
* and limitations under the License.
* -------------------------------------------------------------------
*/
/****************************************************************************************
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.
****************************************************************************************/
/*
Pathname: ./audio/gsm-amr/c/src/sqrt_l.c
------------------------------------------------------------------------------
REVISION HISTORY
Description: Updated template. Changed function interface to pass in a
pointer to overflow flag into the function instead of using a
global flag. Changed name of an input pointer from "exp" to "pExp"
for clarity. Removed inclusion of unwanted header files.
Description: Removed inclusion of sqrt_l.tab file. Changed the array name
"table" to "sqrt_l_tbl". Fixed typos.
Who: Date:
Description:
------------------------------------------------------------------------------
*/
/*----------------------------------------------------------------------------
; INCLUDES
----------------------------------------------------------------------------*/
#include "sqrt_l.h"
#include "typedef.h"
#include "basic_op.h"
/*----------------------------------------------------------------------------
; MACROS
; Define module specific macros here
----------------------------------------------------------------------------*/
/*----------------------------------------------------------------------------
; DEFINES
; Include all pre-processor statements here. Include conditional
; compile variables also.
----------------------------------------------------------------------------*/
/*----------------------------------------------------------------------------
; LOCAL FUNCTION DEFINITIONS
; Function Prototype declaration
----------------------------------------------------------------------------*/
/*----------------------------------------------------------------------------
; LOCAL STORE/BUFFER/POINTER DEFINITIONS
; Variable declaration - defined here and used outside this module
----------------------------------------------------------------------------*/
/*
------------------------------------------------------------------------------
FUNCTION NAME: sqrt_l_exp
------------------------------------------------------------------------------
INPUT AND OUTPUT DEFINITIONS
Inputs:
L_x = input value (Word32)
pExp = pointer to right shift to be applied to result
pOverflow = pointer to overflow flag
Outputs:
pOverflow -> if the Inv_sqrt operation resulted in an overflow.
Returns:
L_y = squareroot of L_x (Word32)
Global Variables Used:
None.
Local Variables Needed:
None.
------------------------------------------------------------------------------
FUNCTION DESCRIPTION
This function computes sqrt(L_x), where L_x is positive.
If L_var is negative or zero, the result is 0
The function sqrt(L_x) is approximated by a table and linear
interpolation. The square root is computed using the
following steps:
1- Normalization of L_x.
2- If exponent is even then shift right once.
3- exponent = exponent/2
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- return L_y and exponent so caller can do denormalization
------------------------------------------------------------------------------
REQUIREMENTS
None.
------------------------------------------------------------------------------
REFERENCES
sqrt_l.c, UMTS GSM AMR speech codec, R99 - Version 3.2.0, March 2, 2001
------------------------------------------------------------------------------
PSEUDO-CODE
Word32 sqrt_l_exp ( // o : output value
Word32 L_x, // i : input value
Word16 *exp // o : right shift to be applied to result
)
{
// y = sqrt(x)
// x = f * 2^-e, 0.5 <= f < 1 (normalization)
// y = sqrt(f) * 2^(-e/2)
//
// a) e = 2k --> y = sqrt(f) * 2^-k (k = e div 2,
// 0.707 <= sqrt(f) < 1)
// b) e = 2k+1 --> y = sqrt(f/2) * 2^-k (k = e div 2,
0.5 <= sqrt(f/2) < 0.707)
Word16 e, i, a, tmp;
Word32 L_y;
if (L_x <= (Word32) 0)
{
*exp = 0;
return (Word32) 0;
}
* The reference ETSI code uses a global Overflow flag. In the actual
* implementation a pointer to the overflow flag is passed into the function.
* This pointer is in turn passed into the basic math functions such as add(),
* L_shl(), L_shr(), sub() called by this module.
e = norm_l (L_x) & 0xFFFE; // get next lower EVEN norm. exp
L_x = L_shl (L_x, e); // L_x is normalized to [0.25..1)
*exp = e; // return 2*exponent (or Q1)
L_x = L_shr (L_x, 9);
i = extract_h (L_x); // Extract b25-b31, 16 <= i <= 63
because of normalization
L_x = L_shr (L_x, 1);
a = extract_l (L_x); // Extract b10-b24
a = a & (Word16) 0x7fff;
i = sub (i, 16); // 0 <= i <= 47
L_y = L_deposit_h (table[i]); // table[i] << 16
tmp = sub (table[i], table[i + 1]); // table[i] - table[i+1])
L_y = L_msu (L_y, tmp, a); // L_y -= tmp*a*2
return (L_y);
}
------------------------------------------------------------------------------
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]
------------------------------------------------------------------------------
*/
Word32 sqrt_l_exp( /* o : output value, Q31 */
Word32 L_x, /* i : input value, Q31 */
Word16 *pExp, /* o : right shift to be applied to result, Q1 */
Flag *pOverflow /* i : pointer to overflow flag */
)
{
Word16 e;
Word16 i;
Word16 a;
Word16 tmp;
Word32 L_y;
/*
y = sqrt(x)
x = f * 2^-e, 0.5 <= f < 1 (normalization)
y = sqrt(f) * 2^(-e/2)
a) e = 2k --> y = sqrt(f) * 2^-k (k = e div 2,
0.707 <= sqrt(f) < 1)
b) e = 2k+1 --> y = sqrt(f/2) * 2^-k (k = e div 2,
0.5 <= sqrt(f/2) < 0.707)
*/
if (L_x <= (Word32) 0)
{
*pExp = 0;
return (Word32) 0;
}
e = norm_l(L_x) & 0xFFFE; /* get next lower EVEN norm. exp */
L_x = L_shl(L_x, e, pOverflow); /* L_x is normalized to [0.25..1) */
*pExp = e; /* return 2*exponent (or Q1) */
L_x >>= 10;
i = (Word16)(L_x >> 15) & 63; /* Extract b25-b31, 16<= i <=63 */
/* because of normalization */
a = (Word16)(L_x); /* Extract b10-b24 */
a &= (Word16) 0x7fff;
if (i > 15)
{
i -= 16; /* 0 <= i <= 47 */
}
L_y = L_deposit_h(sqrt_l_tbl[i]); /* sqrt_l_tbl[i] << 16 */
/* sqrt_l_tbl[i] - sqrt_l_tbl[i+1]) */
tmp = sub(sqrt_l_tbl[i], sqrt_l_tbl[i + 1], pOverflow);
L_y = L_msu(L_y, tmp, a, pOverflow); /* L_y -= tmp*a*2 */
/* L_y = L_shr (L_y, *exp); */ /* denormalization done by caller */
return (L_y);
}
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