1 //===-- lib/floatuntitf.c - uint128 -> quad-precision conversion --*- C -*-===//
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 tu_int to quad-precision conversion for the
11 // compiler-rt library in the IEEE-754 default round-to-nearest, ties-to-even
12 // mode.
13 //
14 //===----------------------------------------------------------------------===//
15 
16 #define QUAD_PRECISION
17 #include "fp_lib.h"
18 #include "int_lib.h"
19 
20 /* Returns: convert a tu_int to a fp_t, rounding toward even. */
21 
22 /* Assumption: fp_t is a IEEE 128 bit floating point type
23  *             tu_int is a 128 bit integral type
24  */
25 
26 /* seee eeee eeee eeee mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm |
27  * mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm
28  */
29 
30 #if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
31 COMPILER_RT_ABI fp_t
32 __floatuntitf(tu_int a) {
33     if (a == 0)
34         return 0.0;
35     const unsigned N = sizeof(tu_int) * CHAR_BIT;
36     int sd = N - __clzti2(a);  /* number of significant digits */
37     int e = sd - 1;            /* exponent */
38     if (sd > LDBL_MANT_DIG) {
39         /*  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
40          *  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
41          *                                                12345678901234567890123456
42          *  1 = msb 1 bit
43          *  P = bit LDBL_MANT_DIG-1 bits to the right of 1
44          *  Q = bit LDBL_MANT_DIG bits to the right of 1
45          *  R = "or" of all bits to the right of Q
46          */
47         switch (sd) {
48         case LDBL_MANT_DIG + 1:
49             a <<= 1;
50             break;
51         case LDBL_MANT_DIG + 2:
52             break;
53         default:
54             a = (a >> (sd - (LDBL_MANT_DIG+2))) |
55                 ((a & ((tu_int)(-1) >> ((N + LDBL_MANT_DIG+2) - sd))) != 0);
56         };
57         /* finish: */
58         a |= (a & 4) != 0;  /* Or P into R */
59         ++a;  /* round - this step may add a significant bit */
60         a >>= 2;  /* dump Q and R */
61         /* a is now rounded to LDBL_MANT_DIG or LDBL_MANT_DIG+1 bits */
62         if (a & ((tu_int)1 << LDBL_MANT_DIG)) {
63             a >>= 1;
64             ++e;
65         }
66         /* a is now rounded to LDBL_MANT_DIG bits */
67     } else {
68         a <<= (LDBL_MANT_DIG - sd);
69         /* a is now rounded to LDBL_MANT_DIG bits */
70     }
71 
72     long_double_bits fb;
73     fb.u.high.all = (du_int)(e + 16383) << 48            /* exponent */
74                   | ((a >> 64) & 0x0000ffffffffffffLL);  /* significand */
75     fb.u.low.all = (du_int)(a);
76     return fb.f;
77 }
78 
79 #endif
80