1 | |
---|
2 | /* @(#)z_pow.c 1.0 98/08/13 */ |
---|
3 | |
---|
4 | /* |
---|
5 | FUNCTION |
---|
6 | <<pow>>, <<powf>>---x to the power y |
---|
7 | INDEX |
---|
8 | pow |
---|
9 | INDEX |
---|
10 | powf |
---|
11 | |
---|
12 | |
---|
13 | SYNOPSIS |
---|
14 | #include <math.h> |
---|
15 | double pow(double <[x]>, double <[y]>); |
---|
16 | float pow(float <[x]>, float <[y]>); |
---|
17 | |
---|
18 | DESCRIPTION |
---|
19 | <<pow>> and <<powf>> calculate <[x]> raised to the exponent <[y]>. |
---|
20 | @tex |
---|
21 | (That is, $x^y$.) |
---|
22 | @end tex |
---|
23 | |
---|
24 | RETURNS |
---|
25 | On success, <<pow>> and <<powf>> return the value calculated. |
---|
26 | |
---|
27 | When the argument values would produce overflow, <<pow>> |
---|
28 | returns <<HUGE_VAL>> and set <<errno>> to <<ERANGE>>. If the |
---|
29 | argument <[x]> passed to <<pow>> or <<powf>> is a negative |
---|
30 | noninteger, and <[y]> is also not an integer, then <<errno>> |
---|
31 | is set to <<EDOM>>. If <[x]> and <[y]> are both 0, then |
---|
32 | <<pow>> and <<powf>> return <<1>>. |
---|
33 | |
---|
34 | You can modify error handling for these functions using <<matherr>>. |
---|
35 | |
---|
36 | PORTABILITY |
---|
37 | <<pow>> is ANSI C. <<powf>> is an extension. */ |
---|
38 | |
---|
39 | #include <float.h> |
---|
40 | #include "fdlibm.h" |
---|
41 | #include "zmath.h" |
---|
42 | |
---|
43 | #ifndef _DOUBLE_IS_32BITS |
---|
44 | |
---|
45 | double pow (double x, double y) |
---|
46 | { |
---|
47 | double d, k, t, r = 1.0; |
---|
48 | int n, sign, exponent_is_even_int = 0; |
---|
49 | __uint32_t px; |
---|
50 | |
---|
51 | GET_HIGH_WORD (px, x); |
---|
52 | |
---|
53 | k = modf (y, &d); |
---|
54 | |
---|
55 | if (k == 0.0) |
---|
56 | { |
---|
57 | /* Exponent y is an integer. */ |
---|
58 | if (modf (ldexp (y, -1), &t)) |
---|
59 | { |
---|
60 | /* y is odd. */ |
---|
61 | exponent_is_even_int = 0; |
---|
62 | } |
---|
63 | else |
---|
64 | { |
---|
65 | /* y is even. */ |
---|
66 | exponent_is_even_int = 1; |
---|
67 | } |
---|
68 | } |
---|
69 | |
---|
70 | if (x == 0.0) |
---|
71 | { |
---|
72 | if (y <= 0.0) |
---|
73 | errno = EDOM; |
---|
74 | } |
---|
75 | else if ((t = y * log (fabs (x))) >= BIGX) |
---|
76 | { |
---|
77 | errno = ERANGE; |
---|
78 | if (px & 0x80000000) |
---|
79 | { |
---|
80 | /* x is negative. */ |
---|
81 | if (k) |
---|
82 | { |
---|
83 | /* y is not an integer. */ |
---|
84 | errno = EDOM; |
---|
85 | x = 0.0; |
---|
86 | } |
---|
87 | else if (exponent_is_even_int) |
---|
88 | x = z_infinity.d; |
---|
89 | else |
---|
90 | x = -z_infinity.d; |
---|
91 | } |
---|
92 | else |
---|
93 | { |
---|
94 | x = z_infinity.d; |
---|
95 | } |
---|
96 | } |
---|
97 | else if (t < SMALLX) |
---|
98 | { |
---|
99 | errno = ERANGE; |
---|
100 | x = 0.0; |
---|
101 | } |
---|
102 | else |
---|
103 | { |
---|
104 | if ( !k && fabs(d) <= 32767 ) |
---|
105 | { |
---|
106 | n = (int) d; |
---|
107 | |
---|
108 | if ((sign = (n < 0))) |
---|
109 | n = -n; |
---|
110 | |
---|
111 | while ( n > 0 ) |
---|
112 | { |
---|
113 | if ((unsigned int) n % 2) |
---|
114 | r *= x; |
---|
115 | x *= x; |
---|
116 | n = (unsigned int) n / 2; |
---|
117 | } |
---|
118 | |
---|
119 | if (sign) |
---|
120 | r = 1.0 / r; |
---|
121 | |
---|
122 | return r; |
---|
123 | } |
---|
124 | else |
---|
125 | { |
---|
126 | if ( px & 0x80000000 ) |
---|
127 | { |
---|
128 | /* x is negative. */ |
---|
129 | if ( k ) |
---|
130 | { |
---|
131 | /* y is not an integer. */ |
---|
132 | errno = EDOM; |
---|
133 | return 0.0; |
---|
134 | } |
---|
135 | } |
---|
136 | |
---|
137 | x = exp (t); |
---|
138 | |
---|
139 | if (!exponent_is_even_int) |
---|
140 | { |
---|
141 | if (px & 0x80000000) |
---|
142 | { |
---|
143 | /* y is an odd integer, and x is negative, |
---|
144 | so the result is negative. */ |
---|
145 | GET_HIGH_WORD (px, x); |
---|
146 | px |= 0x80000000; |
---|
147 | SET_HIGH_WORD (x, px); |
---|
148 | } |
---|
149 | } |
---|
150 | } |
---|
151 | } |
---|
152 | |
---|
153 | return x; |
---|
154 | } |
---|
155 | |
---|
156 | #endif _DOUBLE_IS_32BITS |
---|