source: code/trunk/vendor/github.com/andybalholm/brotli/fast_log.go@ 145

Last change on this file since 145 was 145, checked in by Izuru Yakumo, 22 months ago

Updated the Makefile and vendored depedencies

Signed-off-by: Izuru Yakumo <yakumo.izuru@…>
File size: 6.0 KB
Line 
1package brotli
2
3import (
4 "math"
5 "math/bits"
6)
7
8/* Copyright 2013 Google Inc. All Rights Reserved.
9
10 Distributed under MIT license.
11 See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
12*/
13
14/* Utilities for fast computation of logarithms. */
15
16func log2FloorNonZero(n uint) uint32 {
17 return uint32(bits.Len(n)) - 1
18}
19
20/* A lookup table for small values of log2(int) to be used in entropy
21 computation.
22
23 ", ".join(["%.16ff" % x for x in [0.0]+[log2(x) for x in range(1, 256)]]) */
24var kLog2Table = []float32{
25 0.0000000000000000,
26 0.0000000000000000,
27 1.0000000000000000,
28 1.5849625007211563,
29 2.0000000000000000,
30 2.3219280948873622,
31 2.5849625007211561,
32 2.8073549220576042,
33 3.0000000000000000,
34 3.1699250014423126,
35 3.3219280948873626,
36 3.4594316186372978,
37 3.5849625007211565,
38 3.7004397181410922,
39 3.8073549220576037,
40 3.9068905956085187,
41 4.0000000000000000,
42 4.0874628412503400,
43 4.1699250014423122,
44 4.2479275134435852,
45 4.3219280948873626,
46 4.3923174227787607,
47 4.4594316186372973,
48 4.5235619560570131,
49 4.5849625007211570,
50 4.6438561897747244,
51 4.7004397181410926,
52 4.7548875021634691,
53 4.8073549220576037,
54 4.8579809951275728,
55 4.9068905956085187,
56 4.9541963103868758,
57 5.0000000000000000,
58 5.0443941193584534,
59 5.0874628412503400,
60 5.1292830169449664,
61 5.1699250014423122,
62 5.2094533656289501,
63 5.2479275134435852,
64 5.2854022188622487,
65 5.3219280948873626,
66 5.3575520046180838,
67 5.3923174227787607,
68 5.4262647547020979,
69 5.4594316186372973,
70 5.4918530963296748,
71 5.5235619560570131,
72 5.5545888516776376,
73 5.5849625007211570,
74 5.6147098441152083,
75 5.6438561897747244,
76 5.6724253419714961,
77 5.7004397181410926,
78 5.7279204545631996,
79 5.7548875021634691,
80 5.7813597135246599,
81 5.8073549220576046,
82 5.8328900141647422,
83 5.8579809951275719,
84 5.8826430493618416,
85 5.9068905956085187,
86 5.9307373375628867,
87 5.9541963103868758,
88 5.9772799234999168,
89 6.0000000000000000,
90 6.0223678130284544,
91 6.0443941193584534,
92 6.0660891904577721,
93 6.0874628412503400,
94 6.1085244567781700,
95 6.1292830169449672,
96 6.1497471195046822,
97 6.1699250014423122,
98 6.1898245588800176,
99 6.2094533656289510,
100 6.2288186904958804,
101 6.2479275134435861,
102 6.2667865406949019,
103 6.2854022188622487,
104 6.3037807481771031,
105 6.3219280948873617,
106 6.3398500028846252,
107 6.3575520046180847,
108 6.3750394313469254,
109 6.3923174227787598,
110 6.4093909361377026,
111 6.4262647547020979,
112 6.4429434958487288,
113 6.4594316186372982,
114 6.4757334309663976,
115 6.4918530963296748,
116 6.5077946401986964,
117 6.5235619560570131,
118 6.5391588111080319,
119 6.5545888516776376,
120 6.5698556083309478,
121 6.5849625007211561,
122 6.5999128421871278,
123 6.6147098441152092,
124 6.6293566200796095,
125 6.6438561897747253,
126 6.6582114827517955,
127 6.6724253419714952,
128 6.6865005271832185,
129 6.7004397181410917,
130 6.7142455176661224,
131 6.7279204545631988,
132 6.7414669864011465,
133 6.7548875021634691,
134 6.7681843247769260,
135 6.7813597135246599,
136 6.7944158663501062,
137 6.8073549220576037,
138 6.8201789624151887,
139 6.8328900141647422,
140 6.8454900509443757,
141 6.8579809951275719,
142 6.8703647195834048,
143 6.8826430493618416,
144 6.8948177633079437,
145 6.9068905956085187,
146 6.9188632372745955,
147 6.9307373375628867,
148 6.9425145053392399,
149 6.9541963103868758,
150 6.9657842846620879,
151 6.9772799234999168,
152 6.9886846867721664,
153 7.0000000000000000,
154 7.0112272554232540,
155 7.0223678130284544,
156 7.0334230015374501,
157 7.0443941193584534,
158 7.0552824355011898,
159 7.0660891904577721,
160 7.0768155970508317,
161 7.0874628412503400,
162 7.0980320829605272,
163 7.1085244567781700,
164 7.1189410727235076,
165 7.1292830169449664,
166 7.1395513523987937,
167 7.1497471195046822,
168 7.1598713367783891,
169 7.1699250014423130,
170 7.1799090900149345,
171 7.1898245588800176,
172 7.1996723448363644,
173 7.2094533656289492,
174 7.2191685204621621,
175 7.2288186904958804,
176 7.2384047393250794,
177 7.2479275134435861,
178 7.2573878426926521,
179 7.2667865406949019,
180 7.2761244052742384,
181 7.2854022188622487,
182 7.2946207488916270,
183 7.3037807481771031,
184 7.3128829552843557,
185 7.3219280948873617,
186 7.3309168781146177,
187 7.3398500028846243,
188 7.3487281542310781,
189 7.3575520046180847,
190 7.3663222142458151,
191 7.3750394313469254,
192 7.3837042924740528,
193 7.3923174227787607,
194 7.4008794362821844,
195 7.4093909361377026,
196 7.4178525148858991,
197 7.4262647547020979,
198 7.4346282276367255,
199 7.4429434958487288,
200 7.4512111118323299,
201 7.4594316186372973,
202 7.4676055500829976,
203 7.4757334309663976,
204 7.4838157772642564,
205 7.4918530963296748,
206 7.4998458870832057,
207 7.5077946401986964,
208 7.5156998382840436,
209 7.5235619560570131,
210 7.5313814605163119,
211 7.5391588111080319,
212 7.5468944598876373,
213 7.5545888516776376,
214 7.5622424242210728,
215 7.5698556083309478,
216 7.5774288280357487,
217 7.5849625007211561,
218 7.5924570372680806,
219 7.5999128421871278,
220 7.6073303137496113,
221 7.6147098441152075,
222 7.6220518194563764,
223 7.6293566200796095,
224 7.6366246205436488,
225 7.6438561897747244,
226 7.6510516911789290,
227 7.6582114827517955,
228 7.6653359171851765,
229 7.6724253419714952,
230 7.6794800995054464,
231 7.6865005271832185,
232 7.6934869574993252,
233 7.7004397181410926,
234 7.7073591320808825,
235 7.7142455176661224,
236 7.7210991887071856,
237 7.7279204545631996,
238 7.7347096202258392,
239 7.7414669864011465,
240 7.7481928495894596,
241 7.7548875021634691,
242 7.7615512324444795,
243 7.7681843247769260,
244 7.7747870596011737,
245 7.7813597135246608,
246 7.7879025593914317,
247 7.7944158663501062,
248 7.8008998999203047,
249 7.8073549220576037,
250 7.8137811912170374,
251 7.8201789624151887,
252 7.8265484872909159,
253 7.8328900141647422,
254 7.8392037880969445,
255 7.8454900509443757,
256 7.8517490414160571,
257 7.8579809951275719,
258 7.8641861446542798,
259 7.8703647195834048,
260 7.8765169465650002,
261 7.8826430493618425,
262 7.8887432488982601,
263 7.8948177633079446,
264 7.9008668079807496,
265 7.9068905956085187,
266 7.9128893362299619,
267 7.9188632372745955,
268 7.9248125036057813,
269 7.9307373375628867,
270 7.9366379390025719,
271 7.9425145053392399,
272 7.9483672315846778,
273 7.9541963103868758,
274 7.9600019320680806,
275 7.9657842846620870,
276 7.9715435539507720,
277 7.9772799234999168,
278 7.9829935746943104,
279 7.9886846867721664,
280 7.9943534368588578,
281}
282
283/* Faster logarithm for small integers, with the property of log2(0) == 0. */
284func fastLog2(v uint) float64 {
285 if v < uint(len(kLog2Table)) {
286 return float64(kLog2Table[v])
287 }
288
289 return math.Log2(float64(v))
290}
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