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