| /* ------------------------------------------------------------------ |
| * 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/inv_sqrt.c |
| |
| ------------------------------------------------------------------------------ |
| REVISION HISTORY |
| |
| Description: Put file into template. |
| |
| Description: Synchronized file with UMTS version 3.2.0. Updated coding |
| template. Removed unnecessary include files. |
| |
| Description: Replaced basic_op.h with the header files of the math functions |
| used in the file. |
| |
| Description: Made the following changes per comments from Phase 2/3 review: |
| 1. Defined one local variable per line. |
| 2. Used "&=", ">>=", and "+=" in the code. |
| |
| Description: Updated template. Changed function interface to pass in a |
| pointer to overflow flag into the function instead of using a |
| global flag. |
| |
| Description: Removed inclusion of inv_sqrt.tab file. Changed array name |
| from "table" to "inv_sqrt_tbl" |
| |
| Description: Removed math operations that were not needed as functions, |
| this because the numbers themselves will not saturate the |
| operators, so there is not need to check for saturation. |
| |
| Description: Updated copyrigth year, according to code review comments. |
| |
| Description: Replaced "int" and/or "char" with defined types. |
| Added proper casting (Word32) to some left shifting operations |
| |
| Who: Date: |
| Description: |
| |
| ------------------------------------------------------------------------------ |
| */ |
| |
| /*---------------------------------------------------------------------------- |
| ; INCLUDES |
| ----------------------------------------------------------------------------*/ |
| #include "inv_sqrt.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: Inv_sqrt |
| ------------------------------------------------------------------------------ |
| INPUT AND OUTPUT DEFINITIONS |
| |
| Inputs: |
| L_x = input value (Word32) |
| pOverflow = pointer to overflow flag |
| |
| Outputs: |
| pOverflow -> if the Inv_sqrt operation resulted in an overflow. |
| |
| Returns: |
| L_y = inverse squareroot of L_x (Word32) |
| |
| Global Variables Used: |
| None. |
| |
| Local Variables Needed: |
| None. |
| |
| ------------------------------------------------------------------------------ |
| FUNCTION DESCRIPTION |
| |
| This function computes 1/sqrt(L_x), where L_x is positive. |
| If L_x is negative or zero, the result is 1 (3fff ffff). |
| |
| The function 1/sqrt(L_x) is approximated by a table and linear |
| interpolation. The inverse square root is computed using the |
| following steps: |
| 1- Normalization of L_x. |
| 2- If (30-exponent) is even then shift right once. |
| 3- exponent = (30-exponent)/2 +1 |
| 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- L_y >>= exponent |
| |
| ------------------------------------------------------------------------------ |
| REQUIREMENTS |
| |
| None. |
| |
| ------------------------------------------------------------------------------ |
| REFERENCES |
| |
| inv_sqrt.c, UMTS GSM AMR speech codec, R99 - Version 3.2.0, March 2, 2001 |
| |
| ------------------------------------------------------------------------------ |
| PSEUDO-CODE |
| |
| Word32 Inv_sqrt ( // (o) : output value |
| Word32 L_x // (i) : input value |
| ) |
| { |
| Word16 exp, i, a, tmp; |
| Word32 L_y; |
| |
| * 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. |
| |
| if (L_x <= (Word32) 0) |
| return ((Word32) 0x3fffffffL); |
| |
| exp = norm_l (L_x); |
| L_x = L_shl (L_x, exp); // L_x is normalize |
| |
| exp = sub (30, exp); |
| |
| if ((exp & 1) == 0) // If exponent even -> shift right |
| { |
| L_x = L_shr (L_x, 1); |
| } |
| exp = shr (exp, 1); |
| exp = add (exp, 1); |
| |
| 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 |
| a = a & (Word16) 0x7fff; |
| |
| i = sub (i, 16); |
| |
| 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 |
| |
| L_y = L_shr (L_y, exp); // denormalization |
| |
| 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 Inv_sqrt( /* (o) : output value */ |
| Word32 L_x, /* (i) : input value */ |
| Flag * pOverflow /* (i) : pointer to overflow flag */ |
| ) |
| { |
| Word16 exp; |
| Word16 i; |
| Word16 a; |
| Word16 tmp; |
| Word32 L_y; |
| OSCL_UNUSED_ARG(pOverflow); |
| |
| if (L_x <= (Word32) 0) |
| { |
| return ((Word32) 0x3fffffffL); |
| } |
| |
| exp = norm_l(L_x); |
| L_x <<= exp; /* L_x is normalize */ |
| |
| exp = 30 - exp; |
| |
| if ((exp & 1) == 0) /* If exponent even -> shift right */ |
| { |
| L_x >>= 1; |
| } |
| exp >>= 1; |
| exp += 1; |
| |
| L_x >>= 9; |
| i = (Word16)(L_x >> 16); /* Extract b25-b31 */ |
| a = (Word16)(L_x >> 1); /* Extract b10-b24 */ |
| a &= (Word16) 0x7fff; |
| |
| i -= 16; |
| |
| L_y = (Word32)inv_sqrt_tbl[i] << 16; /* inv_sqrt_tbl[i] << 16 */ |
| |
| /* inv_sqrt_tbl[i] - inv_sqrt_tbl[i+1]) */ |
| tmp = inv_sqrt_tbl[i] - inv_sqrt_tbl[i + 1]; |
| /* always a positive number less than 200 */ |
| |
| L_y -= ((Word32)tmp * a) << 1; /* L_y -= tmp*a*2 */ |
| /* always a positive minus a small negative number */ |
| |
| L_y >>= exp; /* denormalization, exp always 0< exp < 31 */ |
| |
| return (L_y); |
| } |
| |
