1 //===-- floatundidf.c - Implement __floatundidf ---------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements __floatundidf for the compiler_rt library.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 // Returns: convert a to a double, rounding toward even.
14 
15 // Assumption: double is a IEEE 64 bit floating point type
16 //             du_int is a 64 bit integral type
17 
18 // seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm
19 // mmmm
20 
21 #include "int_lib.h"
22 
23 #ifndef __SOFT_FP__
24 // Support for systems that have hardware floating-point; we'll set the inexact
25 // flag as a side-effect of this computation.
26 
__floatundidf(du_int a)27 COMPILER_RT_ABI double __floatundidf(du_int a) {
28   static const double twop52 = 4503599627370496.0;           // 0x1.0p52
29   static const double twop84 = 19342813113834066795298816.0; // 0x1.0p84
30   static const double twop84_plus_twop52 =
31       19342813118337666422669312.0; // 0x1.00000001p84
32 
33   union {
34     uint64_t x;
35     double d;
36   } high = {.d = twop84};
37   union {
38     uint64_t x;
39     double d;
40   } low = {.d = twop52};
41 
42   high.x |= a >> 32;
43   low.x |= a & UINT64_C(0x00000000ffffffff);
44 
45   const double result = (high.d - twop84_plus_twop52) + low.d;
46   return result;
47 }
48 
49 #else
50 // Support for systems that don't have hardware floating-point; there are no
51 // flags to set, and we don't want to code-gen to an unknown soft-float
52 // implementation.
53 
__floatundidf(du_int a)54 COMPILER_RT_ABI double __floatundidf(du_int a) {
55   if (a == 0)
56     return 0.0;
57   const unsigned N = sizeof(du_int) * CHAR_BIT;
58   int sd = N - __builtin_clzll(a); // number of significant digits
59   int e = sd - 1;                  // exponent
60   if (sd > DBL_MANT_DIG) {
61     //  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
62     //  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
63     //                                                12345678901234567890123456
64     //  1 = msb 1 bit
65     //  P = bit DBL_MANT_DIG-1 bits to the right of 1
66     //  Q = bit DBL_MANT_DIG bits to the right of 1
67     //  R = "or" of all bits to the right of Q
68     switch (sd) {
69     case DBL_MANT_DIG + 1:
70       a <<= 1;
71       break;
72     case DBL_MANT_DIG + 2:
73       break;
74     default:
75       a = (a >> (sd - (DBL_MANT_DIG + 2))) |
76           ((a & ((du_int)(-1) >> ((N + DBL_MANT_DIG + 2) - sd))) != 0);
77     };
78     // finish:
79     a |= (a & 4) != 0; // Or P into R
80     ++a;               // round - this step may add a significant bit
81     a >>= 2;           // dump Q and R
82     // a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits
83     if (a & ((du_int)1 << DBL_MANT_DIG)) {
84       a >>= 1;
85       ++e;
86     }
87     // a is now rounded to DBL_MANT_DIG bits
88   } else {
89     a <<= (DBL_MANT_DIG - sd);
90     // a is now rounded to DBL_MANT_DIG bits
91   }
92   double_bits fb;
93   fb.u.s.high = ((su_int)(e + 1023) << 20) |      // exponent
94                 ((su_int)(a >> 32) & 0x000FFFFF); // mantissa-high
95   fb.u.s.low = (su_int)a;                         // mantissa-low
96   return fb.f;
97 }
98 #endif
99 
100 #if defined(__ARM_EABI__)
101 #if defined(COMPILER_RT_ARMHF_TARGET)
__aeabi_ul2d(du_int a)102 AEABI_RTABI double __aeabi_ul2d(du_int a) { return __floatundidf(a); }
103 #else
104 COMPILER_RT_ALIAS(__floatundidf, __aeabi_ul2d)
105 #endif
106 #endif
107