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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.
- * -------------------------------------------------------------------
- */
-/*
-
-
-------------------------------------------------------------------------------
- REVISION HISTORY
-
- Description: Modified from original shareware code
-
- Description: Modified to remove instances of pow() and sqrt(), and
- optimized for inclusion in fixed-point version of decoder.
-
- Description: Modified to include comments/optimizations from code review.
- Also, declared appropriate variables as type "const"
-
- Description: Adopted strategy of "one q-format per sfb" strategy, which
- eliminated the array q-format from this function. The q-format the
- random vector is stored in is now returned from the function.
-
- Description: Completely redesigned the routine to allow a simplified
- calculation of the adjusted noise, by eliminating the dependency
- on the band_length. Added polynomial approximation for the
- function 1/sqrt(power). Updated comments and pseudo-code
-
- Description: Modified function description, pseudocode, etc.
-
- Description:
- Modified casting to ensure proper operations for different platforms
-
- Description:
- Eliminiated access to memory for noise seed. Now a local variable is
- used. Also unrolled loops to speed up code.
-
- Description:
- Modified pointer decrement to a pointer increment, to ensure proper
- compiler behavior
-
- Description:
-------------------------------------------------------------------------------
- INPUT AND OUTPUT DEFINITIONS
-
- Inputs: random_array[] = Array for storage of the power-scaled
- random values of length "band_length"
- Int32
-
- band_length = Length of random_array[]
- const Int
-
- pSeed = seed for random number generator
- Int32*
-
- power_scale = scale factor for this particular band
- const Int
-
-
- Local Stores/Buffers/Pointers Needed:
- None
-
- Global Stores/Buffers/Pointers Needed:
- None
-
- Outputs: Function returns the q-format the random vector is stored in.
-
- Pointers and Buffers Modified:
- random_array[] = filled with random numbers scaled
- to the correct power as defined by the input value power_scale.
-
- Local Stores Modified:
- None
-
- Global Stores Modified:
- None
-
-------------------------------------------------------------------------------
- FUNCTION DESCRIPTION
-
- This function generates a vector of uniformly distributed random numbers for
- the PNS block. The random numbers are each scaled by a scale_factor,
- defined in Ref(2) as
-
- 2^(scale_factor/4)
- ------------------
- sqrt(N*MEAN_NRG)
-
- where N == band_length, and MEAN_NRG is defined as...
-
- N-1
- ___
- 1 \
- --- > x(i)^2
- N /__
- i=0
-
- And x is the unscaled vector from the random number generator.
-
- This function takes advantage of the fact that the portion of the
- scale_factor that is divisible by 4 can be simply accounted for by varying
- the q-format.
-
- The scaling of the random numbers is thus broken into the
- equivalent equation below.
-
- 2^(scale_factor%4) 2^(floor(scale_factor/4))
- ------------------ *
- sqrt(N*MEAN_NRG)
-
-
- 2^(scale_factor%4) is stored in a simple 4-element table.
- 2^(floor(scale_factor/4) is accounted for by adjusting the q-format.
- sqrt(N*MEAN_NRG) is calculated and implemented via a polynomial approximation.
-------------------------------------------------------------------------------
- REQUIREMENTS
-
- This function shall produce uniformly distributed random 32-bit integers,
- with signed random values of average energy equal to the results of the ISO
- code's multiplying factor discussed in the FUNCTION DESCRIPTION section.
-
- Please see Ref (2) for a detailed description of the requirements.
-------------------------------------------------------------------------------
- REFERENCES
-
- (1) Numerical Recipes in C Second Edition
- William H. Press Saul A. Teukolsky
- William T. Vetterling Brian P. Flannery
- Page 284
-
- (2) ISO/IEC 14496-3:1999(E)
- Part 3
- Subpart 4.6.12 (Perceptual Noise Substitution)
-
- (3) MPEG-2 NBC Audio Decoder
- "This software module was originally developed by AT&T, Dolby
- Laboratories, Fraunhofer Gesellschaft IIS in the course of development
- of the MPEG-2 NBC/MPEG-4 Audio standard ISO/IEC 13818-7, 14496-1,2 and
- 3. This software module is an implementation of a part of one or more
- MPEG-2 NBC/MPEG-4 Audio tools as specified by the MPEG-2 NBC/MPEG-4
- Audio standard. ISO/IEC gives users of the MPEG-2 NBC/MPEG-4 Audio
- standards free license to this software module or modifications thereof
- for use in hardware or software products claiming conformance to the
- MPEG-2 NBC/MPEG-4 Audio standards. Those intending to use this software
- module in hardware or software products are advised that this use may
- infringe existing patents. The original developer of this software
- module and his/her company, the subsequent editors and their companies,
- and ISO/IEC have no liability for use of this software module or
- modifications thereof in an implementation. Copyright is not released
- for non MPEG-2 NBC/MPEG-4 Audio conforming products.The original
- developer retains full right to use the code for his/her own purpose,
- assign or donate the code to a third party and to inhibit third party
- from using the code for non MPEG-2 NBC/MPEG-4 Audio conforming products.
- This copyright notice must be included in all copies or derivative
- works."
- Copyright(c)1996.
-
-------------------------------------------------------------------------------
- PSEUDO-CODE
-
- power_adj = scale_mod_4[power_scale & 3];
-
- power = 0;
-
- FOR (k=band_length; k > 0; k--)
-
- *(pSeed) = *(pSeed) * 1664525L;
- *(pSeed) = *(pSeed) + 1013904223L;
-
- temp = (Int)(*(pSeed) >> 16);
-
- power = power + ((temp*temp) >> 6);
-
- *(pArray) = (Int32)temp;
-
- pArray = pArray + 1;
-
- ENDFOR
-
- k = 0;
- q_adjust = 30;
-
- IF (power)
- THEN
-
- WHILE ( power > 32767)
-
- power = power >> 1;
- k = k + 1;
-
- ENDWHILE
-
- k = k - 13;
-
- IF (k < 0)
- THEN
- k = -k;
- IF ( k & 1 )
- THEN
- power_adj = (power_adj*SQRT_OF_2)>>14;
- ENDIF
- q_adjust = q_adjust - ( k >> 1);
-
- ELSE IF (k > 0)
- THEN
- IF ( k & 1 )
- THEN
- power_adj = (power_adj*INV_SQRT_OF_2)>>14;
- ENDIF
- q_adjust = q_adjust + ( k >> 1);
- ENDIF
-
- pInvSqrtCoeff = inv_sqrt_coeff;
-
- inv_sqrt_power = (*(pInvSqrtCoeff)* power) >>15;
-
- pInvSqrtCoeff = pInvSqrtCoeff + 1;
-
- inv_sqrt_power = inv_sqrt_power + *(pInvSqrtCoeff);
-
- pInvSqrtCoeff = pInvSqrtCoeff + 1;
-
- FOR ( k=INV_SQRT_POLY_ORDER - 1; k>0; k--)
-
- inv_sqrt_power = ( inv_sqrt_power * power)>>15;
-
- inv_sqrt_power = inv_sqrt_power + *(pInvSqrtCoeff);
-
- pInvSqrtCoeff = pInvSqrtCoeff + 1;
-
- ENDFOR
-
- inv_sqrt_power = (inv_sqrt_power*power_adj)>>13;
-
- FOR (k=band_length; k > 0; k--)
-
- pArray = pArray - 1;
-
- *(pArray) = *(pArray)*inv_sqrt_power;
-
- ENDFOR
-
- ENDIF
-
- q_adjust = q_adjust - (power_scale >> 2);
-
- return q_adjust;
-
-------------------------------------------------------------------------------
- RESOURCES USED
- When the code is written for a specific target processor
- the resources used should be documented below.
-
- STACK USAGE: [stack count for this module] + [variable to represent
- stack usage for each subroutine called]
-
- where: [stack usage variable] = stack usage for [subroutine
- name] (see [filename].ext)
-
- DATA MEMORY USED: x words
-
- PROGRAM MEMORY USED: x words
-
- CLOCK CYCLES: [cycle count equation for this module] + [variable
- used to represent cycle count for each subroutine
- called]
-
- where: [cycle count variable] = cycle count for [subroutine
- name] (see [filename].ext)
-
-------------------------------------------------------------------------------
-*/
-
-
-/*----------------------------------------------------------------------------
-; INCLUDES
-----------------------------------------------------------------------------*/
-#include "pv_audio_type_defs.h"
-#include "gen_rand_vector.h"
-#include "window_block_fxp.h"
-
-/*----------------------------------------------------------------------------
-; MACROS
-; Define module specific macros here
-----------------------------------------------------------------------------*/
-
-/*----------------------------------------------------------------------------
-; DEFINES
-; Include all pre-processor statements here. Include conditional
-; compile variables also.
-----------------------------------------------------------------------------*/
-#define SQRT_OF_2 23170 /* sqrt(2) in Q14 */
-#define INV_SQRT_OF_2 11585 /* 1/sqrt(2) in Q14 */
-#define INV_SQRT_POLY_ORDER 4
-
-/*----------------------------------------------------------------------------
-; LOCAL FUNCTION DEFINITIONS
-; Function Prototype declaration
-----------------------------------------------------------------------------*/
-
-/*----------------------------------------------------------------------------
-; LOCAL STORE/BUFFER/POINTER DEFINITIONS
-; Variable declaration - defined here and used outside this module
-----------------------------------------------------------------------------*/
-
-
-
-/*
- * 2^([0:3]/4) = 1.0000 1.1892 1.4142 1.6818
- */
-const UInt scale_mod_4[4] = { 16384, 19484, 23170, 27554};
-
-/*
- * polynomial approx. in Q12 (type Int)
- */
-
-const Int inv_sqrt_coeff[INV_SQRT_POLY_ORDER+1] =
- { 4680, -17935, 27697, -22326, 11980};
-
-
-/*----------------------------------------------------------------------------
-; 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
-----------------------------------------------------------------------------*/
-
-Int gen_rand_vector(
- Int32 random_array[],
- const Int band_length,
- Int32* pSeed,
- const Int power_scale)
-{
-
- Int k;
- UInt power_adj;
- Int q_adjust = 30;
-
- Int32 temp;
- Int32 seed;
- Int32 power;
-
- Int32* pArray = &random_array[0];
-
- Int32 inv_sqrt_power;
- const Int *pInvSqrtCoeff;
-
- /*
- * The out of the random number generator is scaled is such a way
- * that is independent of the band length.
- * The output is computed as:
- *
- * x(i)
- * output = ------------------ * 2^(power_scale%4) 2^(floor(power_scale/4))
- * bl
- * sqrt( SUM x(i)^2 )
- * 0
- *
- * bl == band length
- */
-
-
- /*
- * get 2^(power_scale%4)
- */
-
-
- power = 0;
-
- seed = *pSeed;
-
- /*
- * band_length is always an even number (check tables in pg.66 IS0 14496-3)
- */
- if (band_length < 0 || band_length > LONG_WINDOW)
- {
- return q_adjust; /* avoid any processing on error condition */
- }
-
- for (k = (band_length >> 1); k != 0; k--)
- {
- /*------------------------------------------------
- Numerical Recipes in C
- Page 284
- ------------------------------------------------*/
- seed *= 1664525L;
- seed += 1013904223L;
-
- temp = seed >> 16;
-
- seed *= 1664525L;
- seed += 1013904223L;
-
- /* shift by 6 make room for band length accumulation */
- power += ((temp * temp) >> 6);
- *pArray++ = temp;
-
- temp = seed >> 16;
- power += ((temp * temp) >> 6);
- *pArray++ = temp;
-
- } /* END for (k=half_band_length; k > 0; k--) */
-
-
- *pSeed = seed;
-
- /*
- * If the distribution is uniform, the power is expected to use between
- * 28 and 27 bits, by shifting down by 13 bits the power will be a
- * Q15 number.
- * For different band lengths, the power uses between 20 and 29 bits
- */
-
-
- k = 0;
-
- if (power)
- {
- /*
- * approximation requires power between 0.5 < power < 1 in Q15.
- */
-
- while (power > 32767)
- {
- power >>= 1;
- k++;
- }
-
- /*
- * expected power bit usage == 27 bits
- */
-
- k -= 13;
-
- power_adj = scale_mod_4[power_scale & 3];
-
- if (k < 0)
- {
- k = -k;
- if (k & 1)
- { /* multiply by sqrt(2) */
- power_adj = (UInt)(((UInt32) power_adj * SQRT_OF_2) >> 14);
- }
- q_adjust -= (k >> 1); /* adjust Q instead of shifting up */
- }
- else if (k > 0)
- {
- if (k & 1)
- { /* multiply by 1/sqrt(2) */
- power_adj = (UInt)(((UInt32) power_adj * INV_SQRT_OF_2) >> 14);
- }
- q_adjust += (k >> 1); /* adjust Q instead of shifting down */
- }
-
- /*
- * Compute 1/sqrt(power), where 0.5 < power < 1.0 is approximated
- * using a polynomial order INV_SQRT_POLY_ORDER
- */
-
- pInvSqrtCoeff = inv_sqrt_coeff;
-
- inv_sqrt_power = (*(pInvSqrtCoeff++) * power) >> 15;
- inv_sqrt_power += *(pInvSqrtCoeff++);
- inv_sqrt_power = (inv_sqrt_power * power) >> 15;
- inv_sqrt_power += *(pInvSqrtCoeff++);
- inv_sqrt_power = (inv_sqrt_power * power) >> 15;
- inv_sqrt_power += *(pInvSqrtCoeff++);
- inv_sqrt_power = (inv_sqrt_power * power) >> 15;
- inv_sqrt_power += *(pInvSqrtCoeff);
-
- inv_sqrt_power = (inv_sqrt_power * power_adj) >> 13;
-
- pArray = &random_array[0];
-
- for (k = (band_length >> 1); k != 0; k--)
- {
- temp = *(pArray) * inv_sqrt_power;
- *(pArray++) = temp;
- temp = *(pArray) * inv_sqrt_power;
- *(pArray++) = temp;
- } /* END for (k=half_band_length; k > 0; k--) */
-
- } /* if(power) */
-
- /*
- * Adjust Q with the value corresponding to 2^(floor(power_scale/4))
- */
-
- q_adjust -= (power_scale >> 2);
-
- return (q_adjust);
-
-} /* gen_rand_vector */
generated by cgit v1.1 at 2024-06-07 09:42:46 +0000