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author | Sean Bartell <wingedtachikoma@gmail.com> | 2011-06-25 21:32:25 -0400 |
---|---|---|
committer | Nils Wallménius <nils@rockbox.org> | 2012-04-25 22:13:20 +0200 |
commit | f40bfc9267b13b54e6379dfe7539447662879d24 (patch) | |
tree | 9b20069d5e62809ff434061ad730096836f916f2 /lib/rbcodec/codecs/libfaad/common.c | |
parent | a0009907de7a0107d49040d8a180f140e2eff299 (diff) | |
download | rockbox-f40bfc9267b13b54e6379dfe7539447662879d24.tar.gz rockbox-f40bfc9267b13b54e6379dfe7539447662879d24.zip |
Add codecs to librbcodec.
Change-Id: Id7f4717d51ed02d67cb9f9cb3c0ada4a81843f97
Reviewed-on: http://gerrit.rockbox.org/137
Reviewed-by: Nils Wallménius <nils@rockbox.org>
Tested-by: Nils Wallménius <nils@rockbox.org>
Diffstat (limited to 'lib/rbcodec/codecs/libfaad/common.c')
-rw-r--r-- | lib/rbcodec/codecs/libfaad/common.c | 440 |
1 files changed, 440 insertions, 0 deletions
diff --git a/lib/rbcodec/codecs/libfaad/common.c b/lib/rbcodec/codecs/libfaad/common.c new file mode 100644 index 0000000000..bedf56a212 --- /dev/null +++ b/lib/rbcodec/codecs/libfaad/common.c | |||
@@ -0,0 +1,440 @@ | |||
1 | /* | ||
2 | ** FAAD2 - Freeware Advanced Audio (AAC) Decoder including SBR decoding | ||
3 | ** Copyright (C) 2003-2004 M. Bakker, Ahead Software AG, http://www.nero.com | ||
4 | ** | ||
5 | ** This program is free software; you can redistribute it and/or modify | ||
6 | ** it under the terms of the GNU General Public License as published by | ||
7 | ** the Free Software Foundation; either version 2 of the License, or | ||
8 | ** (at your option) any later version. | ||
9 | ** | ||
10 | ** This program is distributed in the hope that it will be useful, | ||
11 | ** but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
12 | ** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | ||
13 | ** GNU General Public License for more details. | ||
14 | ** | ||
15 | ** You should have received a copy of the GNU General Public License | ||
16 | ** along with this program; if not, write to the Free Software | ||
17 | ** Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. | ||
18 | ** | ||
19 | ** Any non-GPL usage of this software or parts of this software is strictly | ||
20 | ** forbidden. | ||
21 | ** | ||
22 | ** Commercial non-GPL licensing of this software is possible. | ||
23 | ** For more info contact Ahead Software through Mpeg4AAClicense@nero.com. | ||
24 | ** | ||
25 | ** $Id$ | ||
26 | **/ | ||
27 | |||
28 | /* just some common functions that could be used anywhere */ | ||
29 | |||
30 | #include "common.h" | ||
31 | #include "structs.h" | ||
32 | |||
33 | #include <stdlib.h> | ||
34 | #include "syntax.h" | ||
35 | |||
36 | |||
37 | /* Returns the sample rate index based on the samplerate */ | ||
38 | uint8_t get_sr_index(const uint32_t samplerate) | ||
39 | { | ||
40 | if (92017 <= samplerate) return 0; | ||
41 | if (75132 <= samplerate) return 1; | ||
42 | if (55426 <= samplerate) return 2; | ||
43 | if (46009 <= samplerate) return 3; | ||
44 | if (37566 <= samplerate) return 4; | ||
45 | if (27713 <= samplerate) return 5; | ||
46 | if (23004 <= samplerate) return 6; | ||
47 | if (18783 <= samplerate) return 7; | ||
48 | if (13856 <= samplerate) return 8; | ||
49 | if (11502 <= samplerate) return 9; | ||
50 | if (9391 <= samplerate) return 10; | ||
51 | if (16428320 <= samplerate) return 11; | ||
52 | |||
53 | return 11; | ||
54 | } | ||
55 | |||
56 | /* Returns the sample rate based on the sample rate index */ | ||
57 | uint32_t get_sample_rate(const uint8_t sr_index) | ||
58 | { | ||
59 | static const uint32_t sample_rates[] = | ||
60 | { | ||
61 | 96000, 88200, 64000, 48000, 44100, 32000, | ||
62 | 24000, 22050, 16000, 12000, 11025, 8000 | ||
63 | }; | ||
64 | |||
65 | if (sr_index < 12) | ||
66 | return sample_rates[sr_index]; | ||
67 | |||
68 | return 0; | ||
69 | } | ||
70 | |||
71 | uint8_t max_pred_sfb(const uint8_t sr_index) | ||
72 | { | ||
73 | static const uint8_t pred_sfb_max[] = | ||
74 | { | ||
75 | 33, 33, 38, 40, 40, 40, 41, 41, 37, 37, 37, 34 | ||
76 | }; | ||
77 | |||
78 | |||
79 | if (sr_index < 12) | ||
80 | return pred_sfb_max[sr_index]; | ||
81 | |||
82 | return 0; | ||
83 | } | ||
84 | |||
85 | uint8_t max_tns_sfb(const uint8_t sr_index, const uint8_t object_type, | ||
86 | const uint8_t is_short) | ||
87 | { | ||
88 | /* entry for each sampling rate | ||
89 | * 1 Main/LC long window | ||
90 | * 2 Main/LC short window | ||
91 | * 3 SSR long window | ||
92 | * 4 SSR short window | ||
93 | */ | ||
94 | static const uint8_t tns_sbf_max[][4] = | ||
95 | { | ||
96 | {31, 9, 28, 7}, /* 96000 */ | ||
97 | {31, 9, 28, 7}, /* 88200 */ | ||
98 | {34, 10, 27, 7}, /* 64000 */ | ||
99 | {40, 14, 26, 6}, /* 48000 */ | ||
100 | {42, 14, 26, 6}, /* 44100 */ | ||
101 | {51, 14, 26, 6}, /* 32000 */ | ||
102 | {46, 14, 29, 7}, /* 24000 */ | ||
103 | {46, 14, 29, 7}, /* 22050 */ | ||
104 | {42, 14, 23, 8}, /* 16000 */ | ||
105 | {42, 14, 23, 8}, /* 12000 */ | ||
106 | {42, 14, 23, 8}, /* 11025 */ | ||
107 | {39, 14, 19, 7}, /* 8000 */ | ||
108 | {39, 14, 19, 7}, /* 7350 */ | ||
109 | {0,0,0,0}, | ||
110 | {0,0,0,0}, | ||
111 | {0,0,0,0} | ||
112 | }; | ||
113 | uint8_t i = 0; | ||
114 | |||
115 | if (is_short) i++; | ||
116 | if (object_type == SSR) i += 2; | ||
117 | |||
118 | return tns_sbf_max[sr_index][i]; | ||
119 | } | ||
120 | |||
121 | /* Returns 0 if an object type is decodable, otherwise returns -1 */ | ||
122 | int8_t can_decode_ot(const uint8_t object_type) | ||
123 | { | ||
124 | switch (object_type) | ||
125 | { | ||
126 | case LC: | ||
127 | return 0; | ||
128 | case MAIN: | ||
129 | #ifdef MAIN_DEC | ||
130 | return 0; | ||
131 | #else | ||
132 | return -1; | ||
133 | #endif | ||
134 | case SSR: | ||
135 | #ifdef SSR_DEC | ||
136 | return 0; | ||
137 | #else | ||
138 | return -1; | ||
139 | #endif | ||
140 | case LTP: | ||
141 | #ifdef LTP_DEC | ||
142 | return 0; | ||
143 | #else | ||
144 | return -1; | ||
145 | #endif | ||
146 | |||
147 | /* ER object types */ | ||
148 | #ifdef ERROR_RESILIENCE | ||
149 | case ER_LC: | ||
150 | #ifdef DRM | ||
151 | case DRM_ER_LC: | ||
152 | #endif | ||
153 | return 0; | ||
154 | case ER_LTP: | ||
155 | #ifdef LTP_DEC | ||
156 | return 0; | ||
157 | #else | ||
158 | return -1; | ||
159 | #endif | ||
160 | case LD: | ||
161 | #ifdef LD_DEC | ||
162 | return 0; | ||
163 | #else | ||
164 | return -1; | ||
165 | #endif | ||
166 | #endif | ||
167 | } | ||
168 | |||
169 | return -1; | ||
170 | } | ||
171 | |||
172 | static const uint8_t Parity [256] = { // parity | ||
173 | 0,1,1,0,1,0,0,1,1,0,0,1,0,1,1,0,1,0,0,1,0,1,1,0,0,1,1,0,1,0,0,1, | ||
174 | 1,0,0,1,0,1,1,0,0,1,1,0,1,0,0,1,0,1,1,0,1,0,0,1,1,0,0,1,0,1,1,0, | ||
175 | 1,0,0,1,0,1,1,0,0,1,1,0,1,0,0,1,0,1,1,0,1,0,0,1,1,0,0,1,0,1,1,0, | ||
176 | 0,1,1,0,1,0,0,1,1,0,0,1,0,1,1,0,1,0,0,1,0,1,1,0,0,1,1,0,1,0,0,1, | ||
177 | 1,0,0,1,0,1,1,0,0,1,1,0,1,0,0,1,0,1,1,0,1,0,0,1,1,0,0,1,0,1,1,0, | ||
178 | 0,1,1,0,1,0,0,1,1,0,0,1,0,1,1,0,1,0,0,1,0,1,1,0,0,1,1,0,1,0,0,1, | ||
179 | 0,1,1,0,1,0,0,1,1,0,0,1,0,1,1,0,1,0,0,1,0,1,1,0,0,1,1,0,1,0,0,1, | ||
180 | 1,0,0,1,0,1,1,0,0,1,1,0,1,0,0,1,0,1,1,0,1,0,0,1,1,0,0,1,0,1,1,0 | ||
181 | }; | ||
182 | |||
183 | static uint32_t __r1 = 1; | ||
184 | static uint32_t __r2 = 1; | ||
185 | |||
186 | |||
187 | /* | ||
188 | * This is a simple random number generator with good quality for audio purposes. | ||
189 | * It consists of two polycounters with opposite rotation direction and different | ||
190 | * periods. The periods are coprime, so the total period is the product of both. | ||
191 | * | ||
192 | * ------------------------------------------------------------------------------------------------- | ||
193 | * +-> |31:30:29:28:27:26:25:24:23:22:21:20:19:18:17:16:15:14:13:12:11:10: 9: 8: 7: 6: 5: 4: 3: 2: 1: 0| | ||
194 | * | ------------------------------------------------------------------------------------------------- | ||
195 | * | | | | | | | | ||
196 | * | +--+--+--+-XOR-+--------+ | ||
197 | * | | | ||
198 | * +--------------------------------------------------------------------------------------+ | ||
199 | * | ||
200 | * ------------------------------------------------------------------------------------------------- | ||
201 | * |31:30:29:28:27:26:25:24:23:22:21:20:19:18:17:16:15:14:13:12:11:10: 9: 8: 7: 6: 5: 4: 3: 2: 1: 0| <-+ | ||
202 | * ------------------------------------------------------------------------------------------------- | | ||
203 | * | | | | | | ||
204 | * +--+----XOR----+--+ | | ||
205 | * | | | ||
206 | * +----------------------------------------------------------------------------------------+ | ||
207 | * | ||
208 | * | ||
209 | * The first has an period of 3*5*17*257*65537, the second of 7*47*73*178481, | ||
210 | * which gives a period of 18.410.713.077.675.721.215. The result is the | ||
211 | * XORed values of both generators. | ||
212 | */ | ||
213 | uint32_t random_int(void) | ||
214 | { | ||
215 | uint32_t t1, t2, t3, t4; | ||
216 | |||
217 | t3 = t1 = __r1; t4 = t2 = __r2; // Parity calculation is done via table lookup, this is also available | ||
218 | t1 &= 0xF5; t2 >>= 25; // on CPUs without parity, can be implemented in C and avoid unpredictable | ||
219 | t1 = Parity [t1]; t2 &= 0x63; // jumps and slow rotate through the carry flag operations. | ||
220 | t1 <<= 31; t2 = Parity [t2]; | ||
221 | |||
222 | return (__r1 = (t3 >> 1) | t1 ) ^ (__r2 = (t4 + t4) | t2 ); | ||
223 | } | ||
224 | |||
225 | #define floor_log2(x) bs_generic(x, BS_LOG2) | ||
226 | |||
227 | #ifdef FIXED_POINT | ||
228 | |||
229 | #define TABLE_BITS 6 | ||
230 | /* just take the maximum number of bits for interpolation */ | ||
231 | #define INTERP_BITS (REAL_BITS-TABLE_BITS) | ||
232 | |||
233 | static const real_t pow2_tab[] ICONST_ATTR = { | ||
234 | REAL_CONST(1.000000000000000), REAL_CONST(1.010889286051701), REAL_CONST(1.021897148654117), | ||
235 | REAL_CONST(1.033024879021228), REAL_CONST(1.044273782427414), REAL_CONST(1.055645178360557), | ||
236 | REAL_CONST(1.067140400676824), REAL_CONST(1.078760797757120), REAL_CONST(1.090507732665258), | ||
237 | REAL_CONST(1.102382583307841), REAL_CONST(1.114386742595892), REAL_CONST(1.126521618608242), | ||
238 | REAL_CONST(1.138788634756692), REAL_CONST(1.151189229952983), REAL_CONST(1.163724858777578), | ||
239 | REAL_CONST(1.176396991650281), REAL_CONST(1.189207115002721), REAL_CONST(1.202156731452703), | ||
240 | REAL_CONST(1.215247359980469), REAL_CONST(1.228480536106870), REAL_CONST(1.241857812073484), | ||
241 | REAL_CONST(1.255380757024691), REAL_CONST(1.269050957191733), REAL_CONST(1.282870016078778), | ||
242 | REAL_CONST(1.296839554651010), REAL_CONST(1.310961211524764), REAL_CONST(1.325236643159741), | ||
243 | REAL_CONST(1.339667524053303), REAL_CONST(1.354255546936893), REAL_CONST(1.369002422974591), | ||
244 | REAL_CONST(1.383909881963832), REAL_CONST(1.398979672538311), REAL_CONST(1.414213562373095), | ||
245 | REAL_CONST(1.429613338391970), REAL_CONST(1.445180806977047), REAL_CONST(1.460917794180647), | ||
246 | REAL_CONST(1.476826145939499), REAL_CONST(1.492907728291265), REAL_CONST(1.509164427593423), | ||
247 | REAL_CONST(1.525598150744538), REAL_CONST(1.542210825407941), REAL_CONST(1.559004400237837), | ||
248 | REAL_CONST(1.575980845107887), REAL_CONST(1.593142151342267), REAL_CONST(1.610490331949254), | ||
249 | REAL_CONST(1.628027421857348), REAL_CONST(1.645755478153965), REAL_CONST(1.663676580326736), | ||
250 | REAL_CONST(1.681792830507429), REAL_CONST(1.700106353718524), REAL_CONST(1.718619298122478), | ||
251 | REAL_CONST(1.737333835273706), REAL_CONST(1.756252160373300), REAL_CONST(1.775376492526521), | ||
252 | REAL_CONST(1.794709075003107), REAL_CONST(1.814252175500399), REAL_CONST(1.834008086409342), | ||
253 | REAL_CONST(1.853979125083386), REAL_CONST(1.874167634110300), REAL_CONST(1.894575981586966), | ||
254 | REAL_CONST(1.915206561397147), REAL_CONST(1.936061793492294), REAL_CONST(1.957144124175400), | ||
255 | REAL_CONST(1.978456026387951), REAL_CONST(2.000000000000000) | ||
256 | }; | ||
257 | |||
258 | static const real_t log2_tab[] ICONST_ATTR_FAAD_LARGE_IRAM = { | ||
259 | REAL_CONST(0.000000000000000), REAL_CONST(0.022367813028455), REAL_CONST(0.044394119358453), | ||
260 | REAL_CONST(0.066089190457772), REAL_CONST(0.087462841250339), REAL_CONST(0.108524456778169), | ||
261 | REAL_CONST(0.129283016944966), REAL_CONST(0.149747119504682), REAL_CONST(0.169925001442312), | ||
262 | REAL_CONST(0.189824558880017), REAL_CONST(0.209453365628950), REAL_CONST(0.228818690495881), | ||
263 | REAL_CONST(0.247927513443585), REAL_CONST(0.266786540694901), REAL_CONST(0.285402218862248), | ||
264 | REAL_CONST(0.303780748177103), REAL_CONST(0.321928094887362), REAL_CONST(0.339850002884625), | ||
265 | REAL_CONST(0.357552004618084), REAL_CONST(0.375039431346925), REAL_CONST(0.392317422778760), | ||
266 | REAL_CONST(0.409390936137702), REAL_CONST(0.426264754702098), REAL_CONST(0.442943495848728), | ||
267 | REAL_CONST(0.459431618637297), REAL_CONST(0.475733430966398), REAL_CONST(0.491853096329675), | ||
268 | REAL_CONST(0.507794640198696), REAL_CONST(0.523561956057013), REAL_CONST(0.539158811108031), | ||
269 | REAL_CONST(0.554588851677637), REAL_CONST(0.569855608330948), REAL_CONST(0.584962500721156), | ||
270 | REAL_CONST(0.599912842187128), REAL_CONST(0.614709844115208), REAL_CONST(0.629356620079610), | ||
271 | REAL_CONST(0.643856189774725), REAL_CONST(0.658211482751795), REAL_CONST(0.672425341971496), | ||
272 | REAL_CONST(0.686500527183218), REAL_CONST(0.700439718141092), REAL_CONST(0.714245517666123), | ||
273 | REAL_CONST(0.727920454563199), REAL_CONST(0.741466986401147), REAL_CONST(0.754887502163469), | ||
274 | REAL_CONST(0.768184324776926), REAL_CONST(0.781359713524660), REAL_CONST(0.794415866350106), | ||
275 | REAL_CONST(0.807354922057604), REAL_CONST(0.820178962415188), REAL_CONST(0.832890014164742), | ||
276 | REAL_CONST(0.845490050944375), REAL_CONST(0.857980995127572), REAL_CONST(0.870364719583405), | ||
277 | REAL_CONST(0.882643049361841), REAL_CONST(0.894817763307943), REAL_CONST(0.906890595608519), | ||
278 | REAL_CONST(0.918863237274595), REAL_CONST(0.930737337562886), REAL_CONST(0.942514505339240), | ||
279 | REAL_CONST(0.954196310386875), REAL_CONST(0.965784284662087), REAL_CONST(0.977279923499917), | ||
280 | REAL_CONST(0.988684686772166), REAL_CONST(1.000000000000000) | ||
281 | }; | ||
282 | |||
283 | uint32_t pow2_fix(real_t val) | ||
284 | { | ||
285 | uint32_t x1, x2; | ||
286 | uint32_t errcorr; | ||
287 | uint32_t index_frac; | ||
288 | uint32_t retval; | ||
289 | int32_t whole = (val >> REAL_BITS); | ||
290 | |||
291 | /* rest = [0..1] */ | ||
292 | int32_t rest = val - (whole << REAL_BITS); | ||
293 | |||
294 | /* index into pow2_tab */ | ||
295 | int32_t index = (rest >> (REAL_BITS-TABLE_BITS)) & ((1<<TABLE_BITS)-1); | ||
296 | |||
297 | |||
298 | if (val == 0) | ||
299 | return (1<<REAL_BITS); | ||
300 | |||
301 | /* leave INTERP_BITS bits */ | ||
302 | index_frac = rest >> (REAL_BITS-TABLE_BITS-INTERP_BITS); | ||
303 | index_frac = index_frac & ((1<<INTERP_BITS)-1); | ||
304 | |||
305 | if (whole >= 0) | ||
306 | retval = REAL_CONST(1) << whole; | ||
307 | else | ||
308 | retval = REAL_CONST(1) >> -whole; | ||
309 | |||
310 | x1 = pow2_tab[index ]; | ||
311 | x2 = pow2_tab[index + 1]; | ||
312 | errcorr = (index_frac*(x2-x1)) >> INTERP_BITS; | ||
313 | |||
314 | retval = MUL_R(retval, (errcorr + x1)); | ||
315 | |||
316 | return retval; | ||
317 | } | ||
318 | |||
319 | uint32_t pow2_int(real_t val) | ||
320 | { | ||
321 | uint32_t x1, x2; | ||
322 | uint32_t errcorr; | ||
323 | uint32_t index_frac; | ||
324 | uint32_t retval; | ||
325 | int32_t whole = (val >> REAL_BITS); | ||
326 | |||
327 | /* rest = [0..1] */ | ||
328 | int32_t rest = val - (whole << REAL_BITS); | ||
329 | |||
330 | /* index into pow2_tab */ | ||
331 | int32_t index = (rest >> (REAL_BITS-TABLE_BITS)) & ((1<<TABLE_BITS)-1); | ||
332 | |||
333 | |||
334 | if (val == 0) | ||
335 | return 1; | ||
336 | |||
337 | /* leave INTERP_BITS bits */ | ||
338 | index_frac = rest >> (REAL_BITS-TABLE_BITS-INTERP_BITS); | ||
339 | index_frac = index_frac & ((1<<INTERP_BITS)-1); | ||
340 | |||
341 | if (whole >= 0) | ||
342 | retval = 1 << whole; | ||
343 | else | ||
344 | retval = 1 >> -whole; | ||
345 | |||
346 | x1 = pow2_tab[index ]; | ||
347 | x2 = pow2_tab[index + 1]; | ||
348 | errcorr = (index_frac*(x2-x1)) >> INTERP_BITS; | ||
349 | |||
350 | retval = MUL_R(retval, (errcorr + x1)); | ||
351 | |||
352 | return retval; | ||
353 | } | ||
354 | |||
355 | /* ld(x) = ld(x*y/y) = ld(x/y) + ld(y), with y=2^N and [1 <= (x/y) < 2] */ | ||
356 | int32_t log2_int(uint32_t val) | ||
357 | { | ||
358 | uint32_t frac; | ||
359 | int32_t exp = 0; | ||
360 | uint32_t index; | ||
361 | uint32_t index_frac; | ||
362 | uint32_t x1, x2; | ||
363 | uint32_t errcorr; | ||
364 | |||
365 | /* error */ | ||
366 | if (val == 0) | ||
367 | return -10000; | ||
368 | |||
369 | exp = floor_log2(val); | ||
370 | exp -= REAL_BITS; | ||
371 | |||
372 | /* frac = [1..2] */ | ||
373 | if (exp >= 0) | ||
374 | frac = val >> exp; | ||
375 | else | ||
376 | frac = val << -exp; | ||
377 | |||
378 | /* index in the log2 table */ | ||
379 | index = frac >> (REAL_BITS-TABLE_BITS); | ||
380 | |||
381 | /* leftover part for linear interpolation */ | ||
382 | index_frac = frac & ((1<<(REAL_BITS-TABLE_BITS))-1); | ||
383 | |||
384 | /* leave INTERP_BITS bits */ | ||
385 | index_frac = index_frac >> (REAL_BITS-TABLE_BITS-INTERP_BITS); | ||
386 | |||
387 | x1 = log2_tab[index & ((1<<TABLE_BITS)-1)]; | ||
388 | x2 = log2_tab[(index & ((1<<TABLE_BITS)-1)) + 1]; | ||
389 | |||
390 | /* linear interpolation */ | ||
391 | /* retval = exp + ((index_frac)*x2 + (1-index_frac)*x1) */ | ||
392 | |||
393 | errcorr = (index_frac * (x2-x1)) >> INTERP_BITS; | ||
394 | |||
395 | return ((exp+REAL_BITS) << REAL_BITS) + errcorr + x1; | ||
396 | } | ||
397 | |||
398 | /* ld(x) = ld(x*y/y) = ld(x/y) + ld(y), with y=2^N and [1 <= (x/y) < 2] */ | ||
399 | real_t log2_fix(uint32_t val) | ||
400 | { | ||
401 | uint32_t frac; | ||
402 | int8_t exp = 0; | ||
403 | uint32_t index; | ||
404 | uint32_t index_frac; | ||
405 | uint32_t x1, x2; | ||
406 | uint32_t errcorr; | ||
407 | |||
408 | /* error */ | ||
409 | if (val == 0) | ||
410 | return -100000; | ||
411 | |||
412 | exp = floor_log2(val); | ||
413 | exp -= REAL_BITS; | ||
414 | |||
415 | /* frac = [1..2] */ | ||
416 | if (exp >= 0) | ||
417 | frac = val >> exp; | ||
418 | else | ||
419 | frac = val << -exp; | ||
420 | |||
421 | /* index in the log2 table */ | ||
422 | index = frac >> (REAL_BITS-TABLE_BITS); | ||
423 | |||
424 | /* leftover part for linear interpolation */ | ||
425 | index_frac = frac & ((1<<(REAL_BITS-TABLE_BITS))-1); | ||
426 | |||
427 | /* leave INTERP_BITS bits */ | ||
428 | index_frac = index_frac >> (REAL_BITS-TABLE_BITS-INTERP_BITS); | ||
429 | |||
430 | x1 = log2_tab[index & ((1<<TABLE_BITS)-1)]; | ||
431 | x2 = log2_tab[(index & ((1<<TABLE_BITS)-1)) + 1]; | ||
432 | |||
433 | /* linear interpolation */ | ||
434 | /* retval = exp + ((index_frac)*x2 + (1-index_frac)*x1) */ | ||
435 | |||
436 | errcorr = (index_frac * (x2-x1)) >> INTERP_BITS; | ||
437 | |||
438 | return (exp << REAL_BITS) + errcorr + x1; | ||
439 | } | ||
440 | #endif | ||