Chromium Code Reviews
chromiumcodereview-hr@appspot.gserviceaccount.com (chromiumcodereview-hr) | Please choose your nickname with Settings | Help | Chromium Project | Gerrit Changes | Sign out
(44)

Side by Side Diff: fusl/src/math/tgamma.c

Issue 1714623002: [fusl] clang-format fusl (Closed) Base URL: git@github.com:domokit/mojo.git@master
Patch Set: headers too Created 4 years, 10 months ago
Use n/p to move between diff chunks; N/P to move between comments. Draft comments are only viewable by you.
Jump to:
View unified diff | Download patch
OLDNEW
1 /* 1 /*
2 "A Precision Approximation of the Gamma Function" - Cornelius Lanczos (1964) 2 "A Precision Approximation of the Gamma Function" - Cornelius Lanczos (1964)
3 "Lanczos Implementation of the Gamma Function" - Paul Godfrey (2001) 3 "Lanczos Implementation of the Gamma Function" - Paul Godfrey (2001)
4 "An Analysis of the Lanczos Gamma Approximation" - Glendon Ralph Pugh (2004) 4 "An Analysis of the Lanczos Gamma Approximation" - Glendon Ralph Pugh (2004)
5 5
6 approximation method: 6 approximation method:
7 7
8 (x - 0.5) S(x) 8 (x - 0.5) S(x)
9 Gamma(x) = (x + g - 0.5) * ---------------- 9 Gamma(x) = (x + g - 0.5) * ----------------
10 exp(x + g - 0.5) 10 exp(x + g - 0.5)
11 11
12 with 12 with
13 a1 a2 a3 aN 13 a1 a2 a3 aN
14 S(x) ~= [ a0 + ----- + ----- + ----- + ... + ----- ] 14 S(x) ~= [ a0 + ----- + ----- + ----- + ... + ----- ]
15 x + 1 x + 2 x + 3 x + N 15 x + 1 x + 2 x + 3 x + N
16 16
17 with a0, a1, a2, a3,.. aN constants which depend on g. 17 with a0, a1, a2, a3,.. aN constants which depend on g.
18 18
19 for x < 0 the following reflection formula is used: 19 for x < 0 the following reflection formula is used:
20 20
21 Gamma(x)*Gamma(-x) = -pi/(x sin(pi x)) 21 Gamma(x)*Gamma(-x) = -pi/(x sin(pi x))
22 22
23 most ideas and constants are from boost and python 23 most ideas and constants are from boost and python
24 */ 24 */
25 #include "libm.h" 25 #include "libm.h"
26 26
27 static const double pi = 3.141592653589793238462643383279502884; 27 static const double pi = 3.141592653589793238462643383279502884;
28 28
29 /* sin(pi x) with x > 0x1p-100, if sin(pi*x)==0 the sign is arbitrary */ 29 /* sin(pi x) with x > 0x1p-100, if sin(pi*x)==0 the sign is arbitrary */
30 static double sinpi(double x) 30 static double sinpi(double x) {
31 { 31 int n;
32 » int n;
33 32
34 » /* argument reduction: x = |x| mod 2 */ 33 /* argument reduction: x = |x| mod 2 */
35 » /* spurious inexact when x is odd int */ 34 /* spurious inexact when x is odd int */
36 » x = x * 0.5; 35 x = x * 0.5;
37 » x = 2 * (x - floor(x)); 36 x = 2 * (x - floor(x));
38 37
39 » /* reduce x into [-.25,.25] */ 38 /* reduce x into [-.25,.25] */
40 » n = 4 * x; 39 n = 4 * x;
41 » n = (n+1)/2; 40 n = (n + 1) / 2;
42 » x -= n * 0.5; 41 x -= n * 0.5;
43 42
44 » x *= pi; 43 x *= pi;
45 » switch (n) { 44 switch (n) {
46 » default: /* case 4 */ 45 default: /* case 4 */
47 » case 0: 46 case 0:
48 » » return __sin(x, 0, 0); 47 return __sin(x, 0, 0);
49 » case 1: 48 case 1:
50 » » return __cos(x, 0); 49 return __cos(x, 0);
51 » case 2: 50 case 2:
52 » » return __sin(-x, 0, 0); 51 return __sin(-x, 0, 0);
53 » case 3: 52 case 3:
54 » » return -__cos(x, 0); 53 return -__cos(x, 0);
55 » } 54 }
56 } 55 }
57 56
58 #define N 12 57 #define N 12
59 //static const double g = 6.024680040776729583740234375; 58 // static const double g = 6.024680040776729583740234375;
60 static const double gmhalf = 5.524680040776729583740234375; 59 static const double gmhalf = 5.524680040776729583740234375;
61 static const double Snum[N+1] = { 60 static const double Snum[N + 1] = {
62 » 23531376880.410759688572007674451636754734846804940, 61 23531376880.410759688572007674451636754734846804940,
63 » 42919803642.649098768957899047001988850926355848959, 62 42919803642.649098768957899047001988850926355848959,
64 » 35711959237.355668049440185451547166705960488635843, 63 35711959237.355668049440185451547166705960488635843,
65 » 17921034426.037209699919755754458931112671403265390, 64 17921034426.037209699919755754458931112671403265390,
66 » 6039542586.3520280050642916443072979210699388420708, 65 6039542586.3520280050642916443072979210699388420708,
67 » 1439720407.3117216736632230727949123939715485786772, 66 1439720407.3117216736632230727949123939715485786772,
68 » 248874557.86205415651146038641322942321632125127801, 67 248874557.86205415651146038641322942321632125127801,
69 » 31426415.585400194380614231628318205362874684987640, 68 31426415.585400194380614231628318205362874684987640,
70 » 2876370.6289353724412254090516208496135991145378768, 69 2876370.6289353724412254090516208496135991145378768,
71 » 186056.26539522349504029498971604569928220784236328, 70 186056.26539522349504029498971604569928220784236328,
72 » 8071.6720023658162106380029022722506138218516325024, 71 8071.6720023658162106380029022722506138218516325024,
73 » 210.82427775157934587250973392071336271166969580291, 72 210.82427775157934587250973392071336271166969580291,
74 » 2.5066282746310002701649081771338373386264310793408, 73 2.5066282746310002701649081771338373386264310793408,
75 }; 74 };
76 static const double Sden[N+1] = { 75 static const double Sden[N + 1] = {
77 » 0, 39916800, 120543840, 150917976, 105258076, 45995730, 13339535, 76 0, 39916800, 120543840, 150917976, 105258076, 45995730, 13339535,
78 » 2637558, 357423, 32670, 1925, 66, 1, 77 2637558, 357423, 32670, 1925, 66, 1,
79 }; 78 };
80 /* n! for small integer n */ 79 /* n! for small integer n */
81 static const double fact[] = { 80 static const double fact[] = {
82 » 1, 1, 2, 6, 24, 120, 720, 5040.0, 40320.0, 362880.0, 3628800.0, 39916800 .0, 81 1,
83 » 479001600.0, 6227020800.0, 87178291200.0, 1307674368000.0, 2092278988800 0.0, 82 1,
84 » 355687428096000.0, 6402373705728000.0, 121645100408832000.0, 83 2,
85 » 2432902008176640000.0, 51090942171709440000.0, 1124000727777607680000.0, 84 6,
85 24,
86 120,
87 720,
88 5040.0,
89 40320.0,
90 362880.0,
91 3628800.0,
92 39916800.0,
93 479001600.0,
94 6227020800.0,
95 87178291200.0,
96 1307674368000.0,
97 20922789888000.0,
98 355687428096000.0,
99 6402373705728000.0,
100 121645100408832000.0,
101 2432902008176640000.0,
102 51090942171709440000.0,
103 1124000727777607680000.0,
86 }; 104 };
87 105
88 /* S(x) rational function for positive x */ 106 /* S(x) rational function for positive x */
89 static double S(double x) 107 static double S(double x) {
90 { 108 double_t num = 0, den = 0;
91 » double_t num = 0, den = 0; 109 int i;
92 » int i;
93 110
94 » /* to avoid overflow handle large x differently */ 111 /* to avoid overflow handle large x differently */
95 » if (x < 8) 112 if (x < 8)
96 » » for (i = N; i >= 0; i--) { 113 for (i = N; i >= 0; i--) {
97 » » » num = num * x + Snum[i]; 114 num = num * x + Snum[i];
98 » » » den = den * x + Sden[i]; 115 den = den * x + Sden[i];
99 » » } 116 }
100 » else 117 else
101 » » for (i = 0; i <= N; i++) { 118 for (i = 0; i <= N; i++) {
102 » » » num = num / x + Snum[i]; 119 num = num / x + Snum[i];
103 » » » den = den / x + Sden[i]; 120 den = den / x + Sden[i];
104 » » } 121 }
105 » return num/den; 122 return num / den;
106 } 123 }
107 124
108 double tgamma(double x) 125 double tgamma(double x) {
109 { 126 union {
110 » union {double f; uint64_t i;} u = {x}; 127 double f;
111 » double absx, y; 128 uint64_t i;
112 » double_t dy, z, r; 129 } u = {x};
113 » uint32_t ix = u.i>>32 & 0x7fffffff; 130 double absx, y;
114 » int sign = u.i>>63; 131 double_t dy, z, r;
132 uint32_t ix = u.i >> 32 & 0x7fffffff;
133 int sign = u.i >> 63;
115 134
116 » /* special cases */ 135 /* special cases */
117 » if (ix >= 0x7ff00000) 136 if (ix >= 0x7ff00000)
118 » » /* tgamma(nan)=nan, tgamma(inf)=inf, tgamma(-inf)=nan with inval id */ 137 /* tgamma(nan)=nan, tgamma(inf)=inf, tgamma(-inf)=nan with invalid */
119 » » return x + INFINITY; 138 return x + INFINITY;
120 » if (ix < (0x3ff-54)<<20) 139 if (ix < (0x3ff - 54) << 20)
121 » » /* |x| < 2^-54: tgamma(x) ~ 1/x, +-0 raises div-by-zero */ 140 /* |x| < 2^-54: tgamma(x) ~ 1/x, +-0 raises div-by-zero */
122 » » return 1/x; 141 return 1 / x;
123 142
124 » /* integer arguments */ 143 /* integer arguments */
125 » /* raise inexact when non-integer */ 144 /* raise inexact when non-integer */
126 » if (x == floor(x)) { 145 if (x == floor(x)) {
127 » » if (sign) 146 if (sign)
128 » » » return 0/0.0; 147 return 0 / 0.0;
129 » » if (x <= sizeof fact/sizeof *fact) 148 if (x <= sizeof fact / sizeof *fact)
130 » » » return fact[(int)x - 1]; 149 return fact[(int)x - 1];
131 » } 150 }
132 151
133 » /* x >= 172: tgamma(x)=inf with overflow */ 152 /* x >= 172: tgamma(x)=inf with overflow */
134 » /* x =< -184: tgamma(x)=+-0 with underflow */ 153 /* x =< -184: tgamma(x)=+-0 with underflow */
135 » if (ix >= 0x40670000) { /* |x| >= 184 */ 154 if (ix >= 0x40670000) { /* |x| >= 184 */
136 » » if (sign) { 155 if (sign) {
137 » » » FORCE_EVAL((float)(0x1p-126/x)); 156 FORCE_EVAL((float)(0x1p-126 / x));
138 » » » if (floor(x) * 0.5 == floor(x * 0.5)) 157 if (floor(x) * 0.5 == floor(x * 0.5))
139 » » » » return 0; 158 return 0;
140 » » » return -0.0; 159 return -0.0;
141 » » } 160 }
142 » » x *= 0x1p1023; 161 x *= 0x1p1023;
143 » » return x; 162 return x;
144 » } 163 }
145 164
146 » absx = sign ? -x : x; 165 absx = sign ? -x : x;
147 166
148 » /* handle the error of x + g - 0.5 */ 167 /* handle the error of x + g - 0.5 */
149 » y = absx + gmhalf; 168 y = absx + gmhalf;
150 » if (absx > gmhalf) { 169 if (absx > gmhalf) {
151 » » dy = y - absx; 170 dy = y - absx;
152 » » dy -= gmhalf; 171 dy -= gmhalf;
153 » } else { 172 } else {
154 » » dy = y - gmhalf; 173 dy = y - gmhalf;
155 » » dy -= absx; 174 dy -= absx;
156 » } 175 }
157 176
158 » z = absx - 0.5; 177 z = absx - 0.5;
159 » r = S(absx) * exp(-y); 178 r = S(absx) * exp(-y);
160 » if (x < 0) { 179 if (x < 0) {
161 » » /* reflection formula for negative x */ 180 /* reflection formula for negative x */
162 » » /* sinpi(absx) is not 0, integers are already handled */ 181 /* sinpi(absx) is not 0, integers are already handled */
163 » » r = -pi / (sinpi(absx) * absx * r); 182 r = -pi / (sinpi(absx) * absx * r);
164 » » dy = -dy; 183 dy = -dy;
165 » » z = -z; 184 z = -z;
166 » } 185 }
167 » r += dy * (gmhalf+0.5) * r / y; 186 r += dy * (gmhalf + 0.5) * r / y;
168 » z = pow(y, 0.5*z); 187 z = pow(y, 0.5 * z);
169 » y = r * z * z; 188 y = r * z * z;
170 » return y; 189 return y;
171 } 190 }
172 191
173 #if 0 192 #if 0
174 double __lgamma_r(double x, int *sign) 193 double __lgamma_r(double x, int *sign)
175 { 194 {
176 double r, absx; 195 double r, absx;
177 196
178 *sign = 1; 197 *sign = 1;
179 198
180 /* special cases */ 199 /* special cases */
(...skipping 32 matching lines...) Expand 10 before | Expand all | Expand 10 after
213 /* reflection formula for negative x */ 232 /* reflection formula for negative x */
214 x = sinpi(absx); 233 x = sinpi(absx);
215 *sign = 2*!!signbit(x) - 1; 234 *sign = 2*!!signbit(x) - 1;
216 r = log(pi/(fabs(x)*absx)) - r; 235 r = log(pi/(fabs(x)*absx)) - r;
217 } 236 }
218 return r; 237 return r;
219 } 238 }
220 239
221 weak_alias(__lgamma_r, lgamma_r); 240 weak_alias(__lgamma_r, lgamma_r);
222 #endif 241 #endif
OLDNEW

Powered by Google App Engine
This is Rietveld 408576698