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 /****************************************************************************************
19 Portions 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)
26 Permission to distribute, modify and use this file under the standard license
27 terms listed above has been obtained from the copyright holder.
28 ****************************************************************************************/
29 /*
30
31 Pathname: ./audio/gsm-amr/c/src/sqrt_l.c
32
33 ------------------------------------------------------------------------------
34 REVISION HISTORY
35
36
37 Description: Updated template. Changed function interface to pass in a
38 pointer to overflow flag into the function instead of using a
39 global flag. Changed name of an input pointer from "exp" to "pExp"
40 for clarity. Removed inclusion of unwanted header files.
41
42 Description: Removed inclusion of sqrt_l.tab file. Changed the array name
43 "table" to "sqrt_l_tbl". Fixed typos.
44
45 Who: Date:
46 Description:
47
48 ------------------------------------------------------------------------------
49 */
50
51 /*----------------------------------------------------------------------------
52 ; INCLUDES
53 ----------------------------------------------------------------------------*/
54 #include "sqrt_l.h"
55 #include "typedef.h"
56 #include "basic_op.h"
57
58 /*----------------------------------------------------------------------------
59 ; MACROS
60 ; Define module specific macros here
61 ----------------------------------------------------------------------------*/
62
63
64 /*----------------------------------------------------------------------------
65 ; DEFINES
66 ; Include all pre-processor statements here. Include conditional
67 ; compile variables also.
68 ----------------------------------------------------------------------------*/
69
70
71 /*----------------------------------------------------------------------------
72 ; LOCAL FUNCTION DEFINITIONS
73 ; Function Prototype declaration
74 ----------------------------------------------------------------------------*/
75
76
77 /*----------------------------------------------------------------------------
78 ; LOCAL STORE/BUFFER/POINTER DEFINITIONS
79 ; Variable declaration - defined here and used outside this module
80 ----------------------------------------------------------------------------*/
81
82
83 /*
84 ------------------------------------------------------------------------------
85 FUNCTION NAME: sqrt_l_exp
86 ------------------------------------------------------------------------------
87 INPUT AND OUTPUT DEFINITIONS
88
89 Inputs:
90 L_x = input value (Word32)
91 pExp = pointer to right shift to be applied to result
92 pOverflow = pointer to overflow flag
93
94 Outputs:
95 pOverflow -> if the Inv_sqrt operation resulted in an overflow.
96
97 Returns:
98 L_y = squareroot of L_x (Word32)
99
100 Global Variables Used:
101 None.
102
103 Local Variables Needed:
104 None.
105
106 ------------------------------------------------------------------------------
107 FUNCTION DESCRIPTION
108
109 This function computes sqrt(L_x), where L_x is positive.
110 If L_var is negative or zero, the result is 0
111
112 The function sqrt(L_x) is approximated by a table and linear
113 interpolation. The square root is computed using the
114 following steps:
115 1- Normalization of L_x.
116 2- If exponent is even then shift right once.
117 3- exponent = exponent/2
118 4- i = bit25-b31 of L_x; 16<=i<=63 because of normalization.
119 5- a = bit10-b24
120 6- i -=16
121 7- L_y = table[i]<<16 - (table[i] - table[i+1]) * a * 2
122 8- return L_y and exponent so caller can do denormalization
123
124 ------------------------------------------------------------------------------
125 REQUIREMENTS
126
127 None.
128
129 ------------------------------------------------------------------------------
130 REFERENCES
131
132 sqrt_l.c, UMTS GSM AMR speech codec, R99 - Version 3.2.0, March 2, 2001
133
134 ------------------------------------------------------------------------------
135 PSEUDO-CODE
136
137 Word32 sqrt_l_exp ( // o : output value
138 Word32 L_x, // i : input value
139 Word16 *exp // o : right shift to be applied to result
140 )
141 {
142
143 // y = sqrt(x)
144 // x = f * 2^-e, 0.5 <= f < 1 (normalization)
145 // y = sqrt(f) * 2^(-e/2)
146 //
147 // a) e = 2k --> y = sqrt(f) * 2^-k (k = e div 2,
148 // 0.707 <= sqrt(f) < 1)
149 // b) e = 2k+1 --> y = sqrt(f/2) * 2^-k (k = e div 2,
150 0.5 <= sqrt(f/2) < 0.707)
151
152
153 Word16 e, i, a, tmp;
154 Word32 L_y;
155
156 if (L_x <= (Word32) 0)
157 {
158 *exp = 0;
159 return (Word32) 0;
160 }
161
162 * The reference ETSI code uses a global Overflow flag. In the actual
163 * implementation a pointer to the overflow flag is passed into the function.
164 * This pointer is in turn passed into the basic math functions such as add(),
165 * L_shl(), L_shr(), sub() called by this module.
166
167 e = norm_l (L_x) & 0xFFFE; // get next lower EVEN norm. exp
168 L_x = L_shl (L_x, e); // L_x is normalized to [0.25..1)
169 *exp = e; // return 2*exponent (or Q1)
170
171 L_x = L_shr (L_x, 9);
172 i = extract_h (L_x); // Extract b25-b31, 16 <= i <= 63
173 because of normalization
174 L_x = L_shr (L_x, 1);
175 a = extract_l (L_x); // Extract b10-b24
176 a = a & (Word16) 0x7fff;
177
178 i = sub (i, 16); // 0 <= i <= 47
179
180 L_y = L_deposit_h (table[i]); // table[i] << 16
181 tmp = sub (table[i], table[i + 1]); // table[i] - table[i+1])
182 L_y = L_msu (L_y, tmp, a); // L_y -= tmp*a*2
183
184 return (L_y);
185 }
186
187 ------------------------------------------------------------------------------
188 RESOURCES USED [optional]
189
190 When the code is written for a specific target processor the
191 the resources used should be documented below.
192
193 HEAP MEMORY USED: x bytes
194
195 STACK MEMORY USED: x bytes
196
197 CLOCK CYCLES: (cycle count equation for this function) + (variable
198 used to represent cycle count for each subroutine
199 called)
200 where: (cycle count variable) = cycle count for [subroutine
201 name]
202
203 ------------------------------------------------------------------------------
204 CAUTION [optional]
205 [State any special notes, constraints or cautions for users of this function]
206
207 ------------------------------------------------------------------------------
208 */
209
sqrt_l_exp(Word32 L_x,Word16 * pExp,Flag * pOverflow)210 Word32 sqrt_l_exp( /* o : output value, Q31 */
211 Word32 L_x, /* i : input value, Q31 */
212 Word16 *pExp, /* o : right shift to be applied to result, Q1 */
213 Flag *pOverflow /* i : pointer to overflow flag */
214 )
215
216 {
217 Word16 e;
218 Word16 i;
219 Word16 a;
220 Word16 tmp;
221 Word32 L_y;
222
223 /*
224 y = sqrt(x)
225 x = f * 2^-e, 0.5 <= f < 1 (normalization)
226 y = sqrt(f) * 2^(-e/2)
227 a) e = 2k --> y = sqrt(f) * 2^-k (k = e div 2,
228 0.707 <= sqrt(f) < 1)
229 b) e = 2k+1 --> y = sqrt(f/2) * 2^-k (k = e div 2,
230 0.5 <= sqrt(f/2) < 0.707)
231 */
232
233 if (L_x <= (Word32) 0)
234 {
235 *pExp = 0;
236 return (Word32) 0;
237 }
238
239 e = norm_l(L_x) & 0xFFFE; /* get next lower EVEN norm. exp */
240 L_x = L_shl(L_x, e, pOverflow); /* L_x is normalized to [0.25..1) */
241 *pExp = e; /* return 2*exponent (or Q1) */
242
243 L_x >>= 10;
244 i = (Word16)(L_x >> 15) & 63; /* Extract b25-b31, 16<= i <=63 */
245 /* because of normalization */
246
247 a = (Word16)(L_x); /* Extract b10-b24 */
248 a &= (Word16) 0x7fff;
249
250 if (i > 15)
251 {
252 i -= 16; /* 0 <= i <= 47 */
253 }
254
255 L_y = L_deposit_h(sqrt_l_tbl[i]); /* sqrt_l_tbl[i] << 16 */
256
257 /* sqrt_l_tbl[i] - sqrt_l_tbl[i+1]) */
258 tmp = sub(sqrt_l_tbl[i], sqrt_l_tbl[i + 1], pOverflow);
259
260 L_y = L_msu(L_y, tmp, a, pOverflow); /* L_y -= tmp*a*2 */
261
262 /* L_y = L_shr (L_y, *exp); */ /* denormalization done by caller */
263
264 return (L_y);
265 }
266
267