| /* ------------------------------------------------------------------ |
| * 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; |
| } |
