1 |
|
|
/*===-- floatdidf.c - Implement __floatdidf -------------------------------=== |
2 |
|
|
* |
3 |
|
|
* The LLVM Compiler Infrastructure |
4 |
|
|
* |
5 |
|
|
* This file is dual licensed under the MIT and the University of Illinois Open |
6 |
|
|
* Source Licenses. See LICENSE.TXT for details. |
7 |
|
|
* |
8 |
|
|
*===----------------------------------------------------------------------=== |
9 |
|
|
* |
10 |
|
|
* This file implements __floatdidf for the compiler_rt library. |
11 |
|
|
* |
12 |
|
|
*===----------------------------------------------------------------------=== |
13 |
|
|
*/ |
14 |
|
|
|
15 |
|
|
#include "int_lib.h" |
16 |
|
|
|
17 |
|
|
/* Returns: convert a to a double, rounding toward even. */ |
18 |
|
|
|
19 |
|
|
/* Assumption: double is a IEEE 64 bit floating point type |
20 |
|
|
* di_int is a 64 bit integral type |
21 |
|
|
*/ |
22 |
|
|
|
23 |
|
|
/* seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm */ |
24 |
|
|
|
25 |
|
|
ARM_EABI_FNALIAS(l2d, floatdidf) |
26 |
|
|
|
27 |
|
|
#ifndef __SOFT_FP__ |
28 |
|
|
/* Support for systems that have hardware floating-point; we'll set the inexact flag |
29 |
|
|
* as a side-effect of this computation. |
30 |
|
|
*/ |
31 |
|
|
|
32 |
|
|
COMPILER_RT_ABI double |
33 |
|
|
__floatdidf(di_int a) |
34 |
|
|
{ |
35 |
|
|
static const double twop52 = 4503599627370496.0; // 0x1.0p52 |
36 |
|
|
static const double twop32 = 4294967296.0; // 0x1.0p32 |
37 |
|
|
|
38 |
|
|
union { int64_t x; double d; } low = { .d = twop52 }; |
39 |
|
|
|
40 |
|
|
const double high = (int32_t)(a >> 32) * twop32; |
41 |
|
|
low.x |= a & INT64_C(0x00000000ffffffff); |
42 |
|
|
|
43 |
|
|
const double result = (high - twop52) + low.d; |
44 |
|
|
return result; |
45 |
|
|
} |
46 |
|
|
|
47 |
|
|
#else |
48 |
|
|
/* Support for systems that don't have hardware floating-point; there are no flags to |
49 |
|
|
* set, and we don't want to code-gen to an unknown soft-float implementation. |
50 |
|
|
*/ |
51 |
|
|
|
52 |
|
|
COMPILER_RT_ABI double |
53 |
|
|
__floatdidf(di_int a) |
54 |
|
|
{ |
55 |
|
|
if (a == 0) |
56 |
|
|
return 0.0; |
57 |
|
|
const unsigned N = sizeof(di_int) * CHAR_BIT; |
58 |
|
|
const di_int s = a >> (N-1); |
59 |
|
|
a = (a ^ s) - s; |
60 |
|
|
int sd = N - __builtin_clzll(a); /* number of significant digits */ |
61 |
|
|
int e = sd - 1; /* exponent */ |
62 |
|
|
if (sd > DBL_MANT_DIG) |
63 |
|
|
{ |
64 |
|
|
/* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx |
65 |
|
|
* finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR |
66 |
|
|
* 12345678901234567890123456 |
67 |
|
|
* 1 = msb 1 bit |
68 |
|
|
* P = bit DBL_MANT_DIG-1 bits to the right of 1 |
69 |
|
|
* Q = bit DBL_MANT_DIG bits to the right of 1 |
70 |
|
|
* R = "or" of all bits to the right of Q |
71 |
|
|
*/ |
72 |
|
|
switch (sd) |
73 |
|
|
{ |
74 |
|
|
case DBL_MANT_DIG + 1: |
75 |
|
|
a <<= 1; |
76 |
|
|
break; |
77 |
|
|
case DBL_MANT_DIG + 2: |
78 |
|
|
break; |
79 |
|
|
default: |
80 |
|
|
a = ((du_int)a >> (sd - (DBL_MANT_DIG+2))) | |
81 |
|
|
((a & ((du_int)(-1) >> ((N + DBL_MANT_DIG+2) - sd))) != 0); |
82 |
|
|
}; |
83 |
|
|
/* finish: */ |
84 |
|
|
a |= (a & 4) != 0; /* Or P into R */ |
85 |
|
|
++a; /* round - this step may add a significant bit */ |
86 |
|
|
a >>= 2; /* dump Q and R */ |
87 |
|
|
/* a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits */ |
88 |
|
|
if (a & ((du_int)1 << DBL_MANT_DIG)) |
89 |
|
|
{ |
90 |
|
|
a >>= 1; |
91 |
|
|
++e; |
92 |
|
|
} |
93 |
|
|
/* a is now rounded to DBL_MANT_DIG bits */ |
94 |
|
|
} |
95 |
|
|
else |
96 |
|
|
{ |
97 |
|
|
a <<= (DBL_MANT_DIG - sd); |
98 |
|
|
/* a is now rounded to DBL_MANT_DIG bits */ |
99 |
|
|
} |
100 |
|
|
double_bits fb; |
101 |
|
|
fb.u.s.high = ((su_int)s & 0x80000000) | /* sign */ |
102 |
|
|
((e + 1023) << 20) | /* exponent */ |
103 |
|
|
((su_int)(a >> 32) & 0x000FFFFF); /* mantissa-high */ |
104 |
|
|
fb.u.s.low = (su_int)a; /* mantissa-low */ |
105 |
|
|
return fb.f; |
106 |
|
|
} |
107 |
|
|
#endif |