| /* ------------------------------------------------------------------ |
| * 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. |
| * ------------------------------------------------------------------- |
| */ |
| /* |
| |
| Filename: pv_log2.c |
| |
| ------------------------------------------------------------------------------ |
| REVISION HISTORY |
| |
| |
| Who: Date: MM/DD/YYYY |
| Description: |
| |
| ------------------------------------------------------------------------------ |
| INPUT AND OUTPUT DEFINITIONS |
| |
| Int32 x 32-bit integer input |
| |
| |
| ------------------------------------------------------------------------------ |
| FUNCTION DESCRIPTION |
| |
| Implement the logarithm base 2 of a number |
| ------------------------------------------------------------------------------ |
| REQUIREMENTS |
| |
| |
| ------------------------------------------------------------------------------ |
| REFERENCES |
| |
| ------------------------------------------------------------------------------ |
| PSEUDO-CODE |
| |
| ------------------------------------------------------------------------------ |
| */ |
| |
| |
| /*---------------------------------------------------------------------------- |
| ; INCLUDES |
| ----------------------------------------------------------------------------*/ |
| |
| #ifdef AAC_PLUS |
| |
| |
| #include "pv_log2.h" |
| #include "fxp_mul32.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 |
| ----------------------------------------------------------------------------*/ |
| |
| #define R_SHIFT 20 |
| #define Q_fmt(x) (Int32)(x*((Int32)1<<R_SHIFT) + (x>=0?0.5F:-0.5F)) |
| |
| const Int32 log_table[9] = |
| { |
| Q_fmt(-0.00879832091331F), Q_fmt(0.12022974263833F), |
| Q_fmt(-0.72883958314294F), Q_fmt(2.57909824242332F), |
| Q_fmt(-5.90041216630330F), Q_fmt(9.15023342527264F), |
| Q_fmt(-9.90616619500413F), Q_fmt(8.11228968755409F), |
| Q_fmt(-3.41763474309898F) |
| }; |
| |
| |
| /*---------------------------------------------------------------------------- |
| ; 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 |
| ----------------------------------------------------------------------------*/ |
| |
| |
| |
| Int32 pv_log2(Int32 z) |
| { |
| const Int32 *pt_table = log_table; |
| Int32 y; |
| Int32 i; |
| |
| Int32 int_log2 = 0; |
| |
| if (z > Q_fmt(2.0f)) |
| { |
| while (z > Q_fmt(2.0f)) |
| { |
| z >>= 1; |
| int_log2++; |
| } |
| } |
| else if (z < Q_fmt(1.0f)) |
| { |
| { |
| while (z < Q_fmt(1.0f)) |
| { |
| z <<= 1; |
| int_log2--; |
| } |
| } |
| } |
| |
| /* |
| * at this point, input limited to 1<x<2 |
| */ |
| |
| if (z != Q_fmt(1.0f)) |
| { |
| y = fxp_mul32_Q20(*(pt_table++), z); |
| |
| for (i = 7; i != 0; i--) |
| { |
| y += *(pt_table++); |
| y = fxp_mul32_Q20(y, z); |
| } |
| |
| y += *(pt_table++); |
| } |
| else |
| { |
| y = 0; |
| } |
| |
| |
| return (y + (int_log2 << 20)); /* Q20 */ |
| } |
| |
| |
| #endif |
| |