pvmp3_alias_reduction.cpp
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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.
* -------------------------------------------------------------------
*/
/*
------------------------------------------------------------------------------
PacketVideo Corp.
MP3 Decoder Library
Filename: pvmp3_alias_reduction.cpp
Date: 09/21/2007
------------------------------------------------------------------------------
REVISION HISTORY
Description:
------------------------------------------------------------------------------
INPUT AND OUTPUT DEFINITIONS
Input
int32 *input_buffer, Ptr to fequency lines of current channel
struct gr_info_s *gr_info, structure with granuke information for the
input
mp3Header *info mp3 header information
------------------------------------------------------------------------------
FUNCTION DESCRIPTION
Alias Reduction
Alias reduction before processing by the IMDCT
Csi +
>---------0---------0-------->
\ / -
Cai \ /
\ /
\ /
\
/ \
Cai / \
/ \ +
>--------0---------0---------->
Csi +
Aliasing Butterfly
Alias reduction is not applied to short blocks
------------------------------------------------------------------------------
REQUIREMENTS
------------------------------------------------------------------------------
REFERENCES
[1] ISO MPEG Audio Subgroup Software Simulation Group (1996)
ISO 13818-3 MPEG-2 Audio Decoder - Lower Sampling Frequency Extension
------------------------------------------------------------------------------
PSEUDO-CODE
1 ci
csi = ---------------- csi = ----------------
sqrt( 1 + (ci^2)) sqrt( 1 + (ci^2))
ci = -0.6, -0.535, -0.33, -0.185, -0.095, -0.041, -0.0142, -0.0037
------------------------------------------------------------------------------
*/
/*----------------------------------------------------------------------------
; INCLUDES
----------------------------------------------------------------------------*/
#include "pvmp3_alias_reduction.h"
#include "pv_mp3dec_fxd_op.h"
/*----------------------------------------------------------------------------
; MACROS
; Define module specific macros here
----------------------------------------------------------------------------*/
/*----------------------------------------------------------------------------
; DEFINES
; Include all pre-processor statements here. Include conditional
; compile variables also.
----------------------------------------------------------------------------*/
#define NUM_BUTTERFLIES 8
#define Q31_fmt(a) (int32(double(0x7FFFFFFF)*a))
/*----------------------------------------------------------------------------
; LOCAL FUNCTION DEFINITIONS
; Function Prototype declaration
----------------------------------------------------------------------------*/
/*----------------------------------------------------------------------------
; LOCAL STORE/BUFFER/POINTER DEFINITIONS
; Variable declaration - defined here and used outside this module
----------------------------------------------------------------------------*/
const int32 c_signal [ NUM_BUTTERFLIES ] =
{
Q31_fmt(0.85749292571254f), Q31_fmt(0.88174199731771f),
Q31_fmt(0.94962864910273f), Q31_fmt(0.98331459249179f),
Q31_fmt(0.99551781606759f), Q31_fmt(0.99916055817815f),
Q31_fmt(0.99989919524445f), Q31_fmt(0.99999315507028f)
};
const int32 c_alias [ NUM_BUTTERFLIES ] =
{
Q31_fmt(-0.51449575542753f), Q31_fmt(-0.47173196856497f),
Q31_fmt(-0.31337745420390f), Q31_fmt(-0.18191319961098f),
Q31_fmt(-0.09457419252642f), Q31_fmt(-0.04096558288530f),
Q31_fmt(-0.01419856857247f), Q31_fmt(-0.00369997467376f)
};
/*----------------------------------------------------------------------------
; EXTERNAL FUNCTION REFERENCES
; Declare functions defined elsewhere and referenced in this module
----------------------------------------------------------------------------*/
/*----------------------------------------------------------------------------
; EXTERNAL GLOBAL STORE/BUFFER/POINTER REFERENCES
; Declare variables used in this module but defined elsewhere
----------------------------------------------------------------------------*/
/*----------------------------------------------------------------------------
; FUNCTION CODE
----------------------------------------------------------------------------*/
void pvmp3_alias_reduction(int32 *input_buffer, /* Ptr to spec values of current channel */
granuleInfo *gr_info,
int32 *used_freq_lines,
mp3Header *info)
{
int32 *ptr1;
int32 *ptr2;
int32 *ptr3;
int32 *ptr4;
const int32 *ptr_csi;
const int32 *ptr_csa;
int32 sblim;
int32 i, j;
*used_freq_lines = fxp_mul32_Q32(*used_freq_lines << 16, (int32)(0x7FFFFFFF / (float)18 - 1.0f)) >> 15;
if (gr_info->window_switching_flag && gr_info->block_type == 2)
{
if (gr_info->mixed_block_flag)
{
sblim = ((info->version_x == MPEG_2_5) && (info->sampling_frequency == 2)) ? 3 : 1;
}
else
{
return; /* illegal parameter */
}
}
else
{
sblim = *used_freq_lines + 1;
if (sblim > SUBBANDS_NUMBER - 1)
{
sblim = SUBBANDS_NUMBER - 1; /* default */
}
}
ptr3 = &input_buffer[17];
ptr4 = &input_buffer[18];
ptr_csi = c_signal;
ptr_csa = c_alias;
/* NUM_BUTTERFLIES (=8) butterflies between each pair of sub-bands*/
for (i = NUM_BUTTERFLIES >> 1; i != 0; i--)
{
int32 csi1 = *ptr_csi++;
int32 csi2 = *ptr_csi++;
int32 csa1 = *ptr_csa++;
int32 csa2 = *ptr_csa++;
ptr1 = ptr3;
ptr3 -= 2;
ptr2 = ptr4;
ptr4 += 2;
/*
* "sblim" alias-reduction operations between each
* pair of sub-bands
*/
for (j = sblim >> 1; j != 0; j--)
{
int32 y = *ptr2;
int32 x = *ptr1 << 1;
*ptr1-- = fxp_msb32_Q32(fxp_mul32_Q32(x, csi1), y << 1, csa1);
*ptr2++ = fxp_mac32_Q32(fxp_mul32_Q32(y << 1, csi1), x, csa1);
y = *ptr2;
x = *ptr1 << 1;
*ptr1 = fxp_msb32_Q32(fxp_mul32_Q32(x, csi2), y << 1, csa2);
*ptr2 = fxp_mac32_Q32(fxp_mul32_Q32(y << 1, csi2), x, csa2);
ptr1 += 19;
ptr2 += 17;
y = *ptr2;
x = *ptr1 << 1;
*ptr1-- = fxp_msb32_Q32(fxp_mul32_Q32(x, csi1), y << 1, csa1);
*ptr2++ = fxp_mac32_Q32(fxp_mul32_Q32(y << 1, csi1), x, csa1);
y = *ptr2;
x = *ptr1 << 1;
*ptr1 = fxp_msb32_Q32(fxp_mul32_Q32(x, csi2), y << 1, csa2);
*ptr2 = fxp_mac32_Q32(fxp_mul32_Q32(y << 1, csi2), x, csa2);
ptr1 += 19;
ptr2 += 17;
}
if (sblim & 1)
{
int32 x = *ptr1 << 1;
int32 y = *ptr2;
*ptr1-- = fxp_msb32_Q32(fxp_mul32_Q32(x, csi1), y << 1, csa1);
*ptr2++ = fxp_mac32_Q32(fxp_mul32_Q32(y << 1, csi1), x, csa1);
x = *ptr1 << 1;
y = *ptr2;
*ptr1 = fxp_msb32_Q32(fxp_mul32_Q32(x, csi2), y << 1, csa2);
*ptr2 = fxp_mac32_Q32(fxp_mul32_Q32(y << 1, csi2), x, csa2);
}
}
}