9 * double x, y, log10();
17 * Returns logarithm to the base 10 of x.
19 * The argument is separated into its exponent and fractional
20 * parts. The logarithm of the fraction is approximated by
22 * log(1+x) = x - 0.5 x**2 + x**3 P(x)/Q(x).
29 * arithmetic domain # trials peak rms
30 * IEEE 0.5, 2.0 30000 1.5e-16 5.0e-17
31 * IEEE 0, MAXNUM 30000 1.4e-16 4.8e-17
32 * DEC 1, MAXNUM 50000 2.5e-17 6.0e-18
34 * In the tests over the interval [1, MAXNUM], the logarithms
35 * of the random arguments were uniformly distributed over
40 * log10 singularity: x = 0; returns -INFINITY
41 * log10 domain: x < 0; returns NAN
45 Cephes Math Library Release 2.8: June, 2000
46 Copyright 1984, 1995, 2000 by Stephen L. Moshier
50 static char fname[] = {"log10"};
52 /* Coefficients for log(1+x) = x - x**2/2 + x**3 P(x)/Q(x)
53 * 1/sqrt(2) <= x < sqrt(2)
57 4.58482948458143443514E-5,
58 4.98531067254050724270E-1,
59 6.56312093769992875930E0,
60 2.97877425097986925891E1,
61 6.06127134467767258030E1,
62 5.67349287391754285487E1,
63 1.98892446572874072159E1
66 /* 1.00000000000000000000E0, */
67 1.50314182634250003249E1,
68 8.27410449222435217021E1,
69 2.20664384982121929218E2,
70 3.07254189979530058263E2,
71 2.14955586696422947765E2,
72 5.96677339718622216300E1
77 static unsigned short P[] = {
78 0034500,0046473,0051374,0135174,
79 0037777,0037566,0145712,0150321,
80 0040722,0002426,0031543,0123107,
81 0041356,0046513,0170752,0004346,
82 0041562,0071553,0023536,0163343,
83 0041542,0170221,0024316,0114216,
84 0041237,0016454,0046611,0104602
86 static unsigned short Q[] = {
87 /*0040200,0000000,0000000,0000000,*/
88 0041160,0100260,0067736,0102424,
89 0041645,0075552,0036563,0147072,
90 0042134,0125025,0021132,0025320,
91 0042231,0120211,0046030,0103271,
92 0042126,0172241,0052151,0120426,
93 0041556,0125702,0072116,0047103
98 static unsigned short P[] = {
99 0x974f,0x6a5f,0x09a7,0x3f08,
100 0x5a1a,0xd979,0xe7ee,0x3fdf,
101 0x74c9,0xc66c,0x40a2,0x401a,
102 0x411d,0x7e3d,0xc9a9,0x403d,
103 0xdcdc,0x64eb,0x4e6d,0x404e,
104 0xd312,0x2519,0x5e12,0x404c,
105 0x3130,0x89b1,0xe3a5,0x4033
107 static unsigned short Q[] = {
108 /*0x0000,0x0000,0x0000,0x3ff0,*/
109 0xd0a2,0x0dfb,0x1016,0x402e,
110 0x79c7,0x47ae,0xaf6d,0x4054,
111 0x455a,0xa44b,0x9542,0x406b,
112 0x10d7,0x2983,0x3411,0x4073,
113 0x3423,0x2a8d,0xde94,0x406a,
114 0xc9c8,0x4e89,0xd578,0x404d
119 static unsigned short P[] = {
120 0x3f08,0x09a7,0x6a5f,0x974f,
121 0x3fdf,0xe7ee,0xd979,0x5a1a,
122 0x401a,0x40a2,0xc66c,0x74c9,
123 0x403d,0xc9a9,0x7e3d,0x411d,
124 0x404e,0x4e6d,0x64eb,0xdcdc,
125 0x404c,0x5e12,0x2519,0xd312,
126 0x4033,0xe3a5,0x89b1,0x3130
128 static unsigned short Q[] = {
129 0x402e,0x1016,0x0dfb,0xd0a2,
130 0x4054,0xaf6d,0x47ae,0x79c7,
131 0x406b,0x9542,0xa44b,0x455a,
132 0x4073,0x3411,0x2983,0x10d7,
133 0x406a,0xde94,0x2a8d,0x3423,
134 0x404d,0xd578,0x4e89,0xc9c8
138 #define SQRTH 0.70710678118654752440
139 #define L102A 3.0078125E-1
140 #define L102B 2.48745663981195213739E-4
141 #define L10EA 4.3359375E-1
142 #define L10EB 7.00731903251827651129E-4
145 extern double frexp ( double, int * );
146 extern double ldexp ( double, int );
147 extern double polevl ( double, void *, int );
148 extern double p1evl ( double, void *, int );
149 extern int isnan ( double );
150 extern int isfinite ( double );
152 double frexp(), ldexp(), polevl(), p1evl();
153 int isnan(), isfinite();
155 extern double LOGE2, SQRT2, INFINITY, NAN;
175 /* Test for domain */
180 mtherr( fname, SING );
185 mtherr( fname, DOMAIN );
190 /* separate mantissa from exponent */
194 e = *q; /* short containing exponent */
195 e = ((e >> 7) & 0377) - 0200; /* the exponent */
196 *q &= 0177; /* strip exponent from x */
197 *q |= 040000; /* x now between 0.5 and 1 */
206 e = ((e >> 4) & 0x0fff) - 0x3fe;
212 /* Equivalent C language standard library function: */
221 /* logarithm using log(1+x) = x - .5x**2 + x**3 P(x)/Q(x) */
226 x = ldexp( x, 1 ) - 1.0; /* 2x - 1 */
236 y = x * ( z * polevl( x, P, 6 ) / p1evl( x, Q, 6 ) );
237 y = y - ldexp( z, -1 ); /* y - 0.5 * x**2 */
239 /* multiply log of fraction by log10(e)
240 * and base 2 exponent by log10(2)
242 z = (x + y) * L10EB; /* accumulate terms in order of size */