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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/log2_norm.c
------------------------------------------------------------------------------
REVISION HISTORY
Description: Created separate file for Log2_norm function.
Description: Synchronized file with UMTS version 3.2.0. Updated coding
template. Removed unnecessary include file.
Description: Made the following changes per comments from Phase 2/3 review:
1. Modified code to improve performance.
2. Fixed typecasting issue with TI C compiler.
3. Added more comments to the code.
Description: Removed unnecessary line of code (line 208).
Description: Removed inclusion of "log2.tab"
Who: Date:
Description:
------------------------------------------------------------------------------
*/
/*----------------------------------------------------------------------------
; INCLUDES
----------------------------------------------------------------------------*/
#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
; Function Prototype declaration
----------------------------------------------------------------------------*/
/*----------------------------------------------------------------------------
; LOCAL STORE/BUFFER/POINTER DEFINITIONS
; Variable declaration - defined here and used outside this module
----------------------------------------------------------------------------*/
/*
------------------------------------------------------------------------------
FUNCTION NAME: Log2_norm
------------------------------------------------------------------------------
INPUT AND OUTPUT DEFINITIONS
Inputs:
L_x = normalized input value of type Word32
exp = number of shifts required to normalize L_x; it is of type Word16
exponent = pointer to the integer part of Log2 (of type Word16)
whose valid range is: 0 <= value <= 30
fraction = pointer to the fractional part of Log2 (of type Word16)
whose valid range is: 0 <= value < 1
Outputs:
exponent points to the newly calculated integer part of Log2
fraction points to the newly calculated fractional part of Log2
Returns:
None
Global Variables Used:
None
Local Variables Needed:
table = Log2 table of constants of type Word16
------------------------------------------------------------------------------
FUNCTION DESCRIPTION
The function Log2(L_x) calculates the logarithm of the normalized input
buffer L_x. The logarithm is approximated by a table and linear
interpolation. The following steps are used to compute Log2(L_x):
1. exponent = 30 - norm_exponent
2. i = bit25-b31 of L_x; 32<=i<=63 (because of normalization).
3. a = bit10-b24
4. i = i - 32
5. fraction = table[i]<<16 - (table[i] - table[i+1]) * a * 2
------------------------------------------------------------------------------
REQUIREMENTS
None
------------------------------------------------------------------------------
REFERENCES
log2.c, UMTS GSM AMR speech codec, R99 - Version 3.2.0, March 2, 2001
------------------------------------------------------------------------------
PSEUDO-CODE
void Log2_norm (
Word32 L_x, // (i) : input value (normalized)
Word16 exp, // (i) : norm_l (L_x)
Word16 *exponent, // (o) : Integer part of Log2. (range: 0<=val<=30)
Word16 *fraction // (o) : Fractional part of Log2. (range: 0<=val<1)
)
{
Word16 i, a, tmp;
Word32 L_y;
if (L_x <= (Word32) 0)
{
*exponent = 0;
*fraction = 0;
return;
}
*exponent = sub (30, exp);
L_x = L_shr (L_x, 9);
i = extract_h (L_x); // Extract b25-b31
L_x = L_shr (L_x, 1);
a = extract_l (L_x); // Extract b10-b24 of fraction
a = a & (Word16) 0x7fff;
i = sub (i, 32);
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
*fraction = extract_h (L_y);
return;
}
------------------------------------------------------------------------------
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]
------------------------------------------------------------------------------
*/
void Log2_norm(
Word32 L_x, /* (i) : input value (normalized) */
Word16 exp, /* (i) : norm_l (L_x) */
Word16 *exponent, /* (o) : Integer part of Log2. (range: 0<=val<=30)*/
Word16 *fraction /* (o) : Fractional part of Log2. (range: 0<=val<1) */
)
{
Word16 i, a, tmp;
Word32 L_y;
if (L_x <= (Word32) 0)
{
*exponent = 0;
*fraction = 0;
}
else
{
/* Calculate exponent portion of Log2 */
*exponent = 30 - exp;
/* At this point, L_x > 0 */
/* Shift L_x to the right by 10 to extract bits 10-31, */
/* which is needed to calculate fractional part of Log2 */
L_x >>= 10;
i = (Word16)(L_x >> 15); /* Extract b25-b31 */
a = L_x & 0x7fff; /* Extract b10-b24 of fraction */
/* Calculate table index -> subtract by 32 is done for */
/* proper table indexing, since 32<=i<=63 (due to normalization) */
i -= 32;
/* Fraction part of Log2 is approximated by using table[] */
/* and linear interpolation, i.e., */
/* fraction = table[i]<<16 - (table[i] - table[i+1]) * a * 2 */
L_y = (Word32) log2_tbl[i] << 16; /* table[i] << 16 */
tmp = log2_tbl[i] - log2_tbl[i + 1]; /* table[i] - table[i+1] */
L_y -= (((Word32) tmp) * a) << 1; /* L_y -= tmp*a*2 */
*fraction = (Word16)(L_y >> 16);
}
return;
}
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