log2_norm.cpp revision 4f1efc098cb5791c3e9f483f2af84aef70d2d0a0 
1/* ------------------------------------------------------------------
2 * Copyright (C) 1998-2009 PacketVideo
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
13 * express or implied.
14 * See the License for the specific language governing permissions
15 * and limitations under the License.
16 * -------------------------------------------------------------------
17 */
18/****************************************************************************************
19Portions of this file are derived from the following 3GPP standard:
20
21    3GPP TS 26.073
22    ANSI-C code for the Adaptive Multi-Rate (AMR) speech codec
23    Available from http://www.3gpp.org
24
25(C) 2004, 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TTA, TTC)
26Permission to distribute, modify and use this file under the standard license
27terms listed above has been obtained from the copyright holder.
28****************************************************************************************/
29/*
30
31 Pathname: ./audio/gsm-amr/c/src/log2_norm.c
32
33------------------------------------------------------------------------------
34 REVISION HISTORY
35
36 Description: Created separate file for Log2_norm function.
37
38 Description: Synchronized file with UMTS version 3.2.0. Updated coding
39              template. Removed unnecessary include file.
40
41 Description: Made the following changes per comments from Phase 2/3 review:
42              1. Modified code to improve performance.
43              2. Fixed typecasting issue with TI C compiler.
44              3. Added more comments to the code.
45
46 Description: Removed unnecessary line of code (line 208).
47
48 Description: Removed inclusion of "log2.tab"
49
50 Who:                           Date:
51 Description:
52
53------------------------------------------------------------------------------
54*/
55
56/*----------------------------------------------------------------------------
57; INCLUDES
58----------------------------------------------------------------------------*/
59#include    "log2_norm.h"
60
61/*----------------------------------------------------------------------------
62; MACROS
63; Define module specific macros here
64----------------------------------------------------------------------------*/
65
66
67/*----------------------------------------------------------------------------
68; DEFINES
69; Include all pre-processor statements here. Include conditional
70; compile variables also.
71----------------------------------------------------------------------------*/
72
73/*----------------------------------------------------------------------------
74; LOCAL FUNCTION DEFINITIONS
75; Function Prototype declaration
76----------------------------------------------------------------------------*/
77
78/*----------------------------------------------------------------------------
79; LOCAL STORE/BUFFER/POINTER DEFINITIONS
80; Variable declaration - defined here and used outside this module
81----------------------------------------------------------------------------*/
82
83
84/*
85------------------------------------------------------------------------------
86 FUNCTION NAME: Log2_norm
87------------------------------------------------------------------------------
88 INPUT AND OUTPUT DEFINITIONS
89
90 Inputs:
91    L_x = normalized input value of type Word32
92    exp = number of shifts required to normalize L_x; it is of type Word16
93    exponent = pointer to the integer part of Log2 (of type Word16)
94           whose valid range is: 0 <= value <= 30
95    fraction = pointer to the fractional part of Log2 (of type Word16)
96           whose valid range is: 0 <= value < 1
97
98 Outputs:
99    exponent points to the newly calculated integer part of Log2
100    fraction points to the newly calculated fractional part of Log2
101
102 Returns:
103    None
104
105 Global Variables Used:
106    None
107
108 Local Variables Needed:
109    table = Log2 table of constants of type Word16
110
111------------------------------------------------------------------------------
112 FUNCTION DESCRIPTION
113
114 The function Log2(L_x) calculates the logarithm of the normalized input
115 buffer L_x. The logarithm is approximated by a table and linear
116 interpolation. The following steps are used to compute Log2(L_x):
117
118 1. exponent = 30 - norm_exponent
119 2. i = bit25-b31 of L_x;  32<=i<=63  (because of normalization).
120 3. a = bit10-b24
121 4. i = i - 32
122 5. fraction = table[i]<<16 - (table[i] - table[i+1]) * a * 2
123
124------------------------------------------------------------------------------
125 REQUIREMENTS
126
127 None
128
129------------------------------------------------------------------------------
130 REFERENCES
131
132 log2.c, UMTS GSM AMR speech codec, R99 - Version 3.2.0, March 2, 2001
133
134------------------------------------------------------------------------------
135 PSEUDO-CODE
136
137void Log2_norm (
138    Word32 L_x,         // (i) : input value (normalized)
139    Word16 exp,         // (i) : norm_l (L_x)
140    Word16 *exponent,   // (o) : Integer part of Log2.   (range: 0<=val<=30)
141    Word16 *fraction    // (o) : Fractional part of Log2. (range: 0<=val<1)
142)
143{
144    Word16 i, a, tmp;
145    Word32 L_y;
146
147    if (L_x <= (Word32) 0)
148    {
149        *exponent = 0;
150        *fraction = 0;
151        return;
152    }
153
154    *exponent = sub (30, exp);
155
156    L_x = L_shr (L_x, 9);
157    i = extract_h (L_x);                // Extract b25-b31
158    L_x = L_shr (L_x, 1);
159    a = extract_l (L_x);                // Extract b10-b24 of fraction
160    a = a & (Word16) 0x7fff;
161
162    i = sub (i, 32);
163
164    L_y = L_deposit_h (table[i]);       // table[i] << 16
165    tmp = sub (table[i], table[i + 1]); // table[i] - table[i+1]
166    L_y = L_msu (L_y, tmp, a);          // L_y -= tmp*a*2
167
168    *fraction = extract_h (L_y);
169
170    return;
171}
172
173------------------------------------------------------------------------------
174 RESOURCES USED [optional]
175
176 When the code is written for a specific target processor the
177 the resources used should be documented below.
178
179 HEAP MEMORY USED: x bytes
180
181 STACK MEMORY USED: x bytes
182
183 CLOCK CYCLES: (cycle count equation for this function) + (variable
184                used to represent cycle count for each subroutine
185                called)
186     where: (cycle count variable) = cycle count for [subroutine
187                                     name]
188
189------------------------------------------------------------------------------
190 CAUTION [optional]
191 [State any special notes, constraints or cautions for users of this function]
192
193------------------------------------------------------------------------------
194*/
195
196void Log2_norm(
197    Word32 L_x,         /* (i) : input value (normalized)                   */
198    Word16 exp,         /* (i) : norm_l (L_x)                               */
199    Word16 *exponent,   /* (o) : Integer part of Log2.   (range: 0<=val<=30)*/
200    Word16 *fraction    /* (o) : Fractional part of Log2. (range: 0<=val<1) */
201)
202{
203    Word16 i, a, tmp;
204    Word32 L_y;
205
206    if (L_x <= (Word32) 0)
207    {
208        *exponent = 0;
209        *fraction = 0;
210    }
211    else
212    {
213        /* Calculate exponent portion of Log2 */
214        *exponent = 30 - exp;
215
216        /* At this point, L_x > 0       */
217        /* Shift L_x to the right by 10 to extract bits 10-31,  */
218        /* which is needed to calculate fractional part of Log2 */
219        L_x >>= 10;
220        i = (Word16)(L_x >> 15);    /* Extract b25-b31 */
221        a = L_x & 0x7fff;           /* Extract b10-b24 of fraction */
222
223        /* Calculate table index -> subtract by 32 is done for           */
224        /* proper table indexing, since 32<=i<=63 (due to normalization) */
225        i -= 32;
226
227        /* Fraction part of Log2 is approximated by using table[]    */
228        /* and linear interpolation, i.e.,                           */
229        /* fraction = table[i]<<16 - (table[i] - table[i+1]) * a * 2 */
230        L_y = (Word32) log2_tbl[i] << 16;  /* table[i] << 16        */
231        tmp = log2_tbl[i] - log2_tbl[i + 1];  /* table[i] - table[i+1] */
232        L_y -= (((Word32) tmp) * a) << 1; /* L_y -= tmp*a*2        */
233
234        *fraction = (Word16)(L_y >> 16);
235    }
236
237    return;
238}
239