1 /* Implementations for copysign, ilogb, and nextafter for float16 based on
2 * corresponding float32 implementations in
3 * bionic/libm/upstream-freebsd/lib/msun/src
4 */
5
6 /*
7 * ====================================================
8 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
9 *
10 * Developed at SunPro, a Sun Microsystems, Inc. business.
11 * Permission to use, copy, modify, and distribute this
12 * software is freely granted, provided that this notice
13 * is preserved.
14 * ====================================================
15 */
16
17 #include "rs_core.rsh"
18 #include "rs_f16_util.h"
19
20 // Based on bionic/libm/upstream-freebsd/lib/msun/src/s_copysignf.c
copysign(half x,half y)21 extern half __attribute__((overloadable)) copysign(half x, half y) {
22 short hx, hy;
23 GET_HALF_WORD(hx, x);
24 GET_HALF_WORD(hy, y);
25
26 SET_HALF_WORD(x, (hx & 0x7fff) | (hy & 0x8000));
27 return x;
28 }
29
30 // Based on bionic/libm/upstream-freebsd/lib/msun/src/s_frexpf.c
frexp(half x,int * eptr)31 extern half __attribute__((overloadable)) frexp(half x, int *eptr) {
32 short hx, ix;
33 static const half two12 = 4096;
34
35 GET_HALF_WORD(hx, x);
36 ix = hx & 0x7fff;
37
38 *eptr = 0;
39 if (ix >= 0x7c00 || ix == 0) return x; // NaN, infinity or zero
40 if (ix <= 0x0400) {
41 // x is subnormal. Scale it by 2^12 (and adjust eptr accordingly) so
42 // that even the smallest subnormal value becomes normal.
43 x *= two12;
44 GET_HALF_WORD(hx, x);
45 ix = hx & 0x7fff;
46 *eptr = -12;
47 }
48
49 // Adjust eptr by (non-biased exponent of hx + 1). Set the non-biased
50 // exponent to be equal to -1 so that abs(hx) is between 0.5 and 1.
51 *eptr += (ix >> 10) - 14;
52 hx = (hx & 0x83ff) | 0x3800;
53 SET_HALF_WORD(x, hx);
54 return x;
55 }
56
57 // Based on bionic/libm/upstream-freebsd/lib/msun/src/s_ilogbf.c
ilogb(half x)58 extern int __attribute__((overloadable)) ilogb(half x) {
59 const int RS_INT_MAX = 0x7fffffff;
60 const int RS_INT_MIN = 0x80000000;
61
62 short hx, ix;
63 GET_HALF_WORD(hx, x);
64 hx &= 0x7fff;
65
66 if (hx < 0x0400) { // subnormal
67 if (hx == 0)
68 return RS_INT_MIN; // for zero
69 for (hx <<= 5, ix = -14; hx > 0; hx <<= 1)
70 ix -= 1;
71 return ix;
72 }
73 else if (hx < 0x7c00) {
74 return (hx >> 10) - 15;
75 }
76 else { // hx >= 0x7c00
77 return RS_INT_MAX; // for NaN and infinity
78 }
79 }
80
81 // Based on bionic/libm/upstream-freebsd/lib/msun/src/s_modff.c
modf(half x,half * iptr)82 extern half __attribute__((overloadable)) modf(half x, half *iptr) {
83 short i0, j0;
84 unsigned short i;
85 GET_HALF_WORD(i0, x);
86 j0 = ((i0 >> 10) & 0x1f) - 15; // exponent of x
87 if (j0 < 10) {
88 if (j0 < 0) { // No integral part
89 SET_HALF_WORD(*iptr, i0 & 0x8000); // *iptr = +/- 0
90 return x;
91 }
92 else {
93 i = 0x03ff >> j0; // mask to check fractional parts of x
94 if ((i0 & i) == 0) { // no bits set in fractional part
95 *iptr = x;
96 SET_HALF_WORD(x, i0 & 0x8000);
97 return x;
98 }
99 else {
100 SET_HALF_WORD(*iptr, i0 & ~i); // zero out fractional parts
101 return x - *iptr;
102 }
103 }
104 }
105 else { // No fractional part
106 unsigned short ix;
107 *iptr = x;
108 if (x != x)
109 return x;
110 GET_HALF_WORD(ix, x);
111 SET_HALF_WORD(x, ix & 0x8000); // x = +/- 0
112 return x;
113 }
114 }
115
116 // Based on bionic/libm/upstream-freebsd/lib/msun/src/s_nextafterf.c
nextafter(half x,half y)117 extern half __attribute__((overloadable)) nextafter(half x, half y) {
118 volatile half t;
119 short hx, hy, ix, iy;
120
121 GET_HALF_WORD(hx, x);
122 GET_HALF_WORD(hy, y);
123 ix = hx & 0x7fff; // |x|
124 iy = hy & 0x7fff; // |y|
125
126 if ((ix > 0x7c00) || // x is nan
127 (iy > 0x7c00)) // y is nan
128 return x + y; // return nan
129
130 if (x == y) return y; // x == y. return y
131 if (ix == 0) {
132 SET_HALF_WORD(x, (hy & 0x8000) | 1);
133 return x;
134 }
135
136 if (hx >= 0) { // x >= 0
137 if (hx > hy)
138 hx -= 1; // x > y, x -= 1 ulp
139 else
140 hx += 1; // x < y, x += 1 ulp
141 }
142 else { // x < 0
143 if (hy>= 0 || hx > hy)
144 hx -= 1; // x < y, x -= 1 ulp
145 else
146 hx += 1;
147 }
148
149 SET_HALF_WORD(x, hx);
150 return x;
151 }
152