math: fix tgamma to raise underflow for large negative values
[oweals/musl.git] / src / math / fmod.c
1 /* origin: FreeBSD /usr/src/lib/msun/src/e_fmod.c */
2 /*
3  * ====================================================
4  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
5  *
6  * Developed at SunSoft, a Sun Microsystems, Inc. business.
7  * Permission to use, copy, modify, and distribute this
8  * software is freely granted, provided that this notice
9  * is preserved.
10  * ====================================================
11  */
12 /*
13  * fmod(x,y)
14  * Return x mod y in exact arithmetic
15  * Method: shift and subtract
16  */
17
18 #include "libm.h"
19
20 static const double Zero[] = {0.0, -0.0,};
21
22 double fmod(double x, double y)
23 {
24         int32_t n,hx,hy,hz,ix,iy,sx,i;
25         uint32_t lx,ly,lz;
26
27         EXTRACT_WORDS(hx, lx, x);
28         EXTRACT_WORDS(hy, ly, y);
29         sx = hx & 0x80000000;  /* sign of x */
30         hx ^= sx;              /* |x| */
31         hy &= 0x7fffffff;      /* |y| */
32
33         /* purge off exception values */
34         if ((hy|ly) == 0 || hx >= 0x7ff00000 ||  /* y=0,or x not finite */
35             (hy|((ly|-ly)>>31)) > 0x7ff00000)    /* or y is NaN */
36                 return (x*y)/(x*y);
37         if (hx <= hy) {
38                 if (hx < hy || lx < ly)  /* |x| < |y| */
39                         return x;
40                 if (lx == ly)            /* |x| = |y|, return x*0 */
41                         return Zero[(uint32_t)sx>>31];
42         }
43
44         /* determine ix = ilogb(x) */
45         if (hx < 0x00100000) {  /* subnormal x */
46                 if (hx == 0) {
47                         for (ix = -1043, i = lx; i > 0; i <<= 1)
48                                 ix -= 1;
49                 } else {
50                         for (ix = -1022, i = hx<<11; i > 0; i <<= 1)
51                                 ix -= 1;
52                 }
53         } else
54                 ix = (hx>>20) - 1023;
55
56         /* determine iy = ilogb(y) */
57         if (hy < 0x00100000) {  /* subnormal y */
58                 if (hy == 0) {
59                         for (iy = -1043, i = ly; i > 0; i <<= 1)
60                                 iy -= 1;
61                 } else {
62                         for (iy = -1022, i = hy<<11; i > 0; i <<= 1)
63                                 iy -= 1;
64                 }
65         } else
66                 iy = (hy>>20) - 1023;
67
68         /* set up {hx,lx}, {hy,ly} and align y to x */
69         if (ix >= -1022)
70                 hx = 0x00100000|(0x000fffff&hx);
71         else {       /* subnormal x, shift x to normal */
72                 n = -1022-ix;
73                 if (n <= 31) {
74                         hx = (hx<<n)|(lx>>(32-n));
75                         lx <<= n;
76                 } else {
77                         hx = lx<<(n-32);
78                         lx = 0;
79                 }
80         }
81         if(iy >= -1022)
82                 hy = 0x00100000|(0x000fffff&hy);
83         else {       /* subnormal y, shift y to normal */
84                 n = -1022-iy;
85                 if (n <= 31) {
86                         hy = (hy<<n)|(ly>>(32-n));
87                         ly <<= n;
88                 } else {
89                         hy = ly<<(n-32);
90                         ly = 0;
91                 }
92         }
93
94         /* fix point fmod */
95         n = ix - iy;
96         while (n--) {
97                 hz = hx-hy;
98                 lz = lx-ly;
99                 if (lx < ly)
100                         hz -= 1;
101                 if (hz < 0) {
102                         hx = hx+hx+(lx>>31);
103                         lx = lx+lx;
104                 } else {
105                         if ((hz|lz) == 0)   /* return sign(x)*0 */
106                                 return Zero[(uint32_t)sx>>31];
107                         hx = hz+hz+(lz>>31);
108                         lx = lz+lz;
109                 }
110         }
111         hz = hx-hy;
112         lz = lx-ly;
113         if (lx < ly)
114                 hz -= 1;
115         if (hz >= 0) {
116                 hx = hz;
117                 lx = lz;
118         }
119
120         /* convert back to floating value and restore the sign */
121         if ((hx|lx) == 0)          /* return sign(x)*0 */
122                 return Zero[(uint32_t)sx>>31];
123         while (hx < 0x00100000) {  /* normalize x */
124                 hx = hx+hx+(lx>>31);
125                 lx = lx+lx;
126                 iy -= 1;
127         }
128         if (iy >= -1022) {         /* normalize output */
129                 hx = ((hx-0x00100000)|((iy+1023)<<20));
130                 INSERT_WORDS(x, hx|sx, lx);
131         } else {                   /* subnormal output */
132                 n = -1022 - iy;
133                 if (n <= 20) {
134                         lx = (lx>>n)|((uint32_t)hx<<(32-n));
135                         hx >>= n;
136                 } else if (n <= 31) {
137                         lx = (hx<<(32-n))|(lx>>n);
138                         hx = sx;
139                 } else {
140                         lx = hx>>(n-32); hx = sx;
141                 }
142                 INSERT_WORDS(x, hx|sx, lx);
143         }
144         return x;  /* exact output */
145 }