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1 /*===-- floatundisf.c - Implement __floatundisf ---------------------------===
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 __floatundisf for the compiler_rt library.
11  *
12  *===----------------------------------------------------------------------===
13  */
14 
15 /* Returns: convert a to a float, rounding toward even. */
16 
17 /* Assumption: float is a IEEE 32 bit floating point type
18  *            du_int is a 64 bit integral type
19  */
20 
21 /* seee eeee emmm mmmm mmmm mmmm mmmm mmmm */
22 
23 #include "int_lib.h"
24 
ARM_EABI_FNALIAS(ul2f,floatundisf)25 ARM_EABI_FNALIAS(ul2f, floatundisf)
26 
27 COMPILER_RT_ABI float
28 __floatundisf(du_int a)
29 {
30     if (a == 0)
31         return 0.0F;
32     const unsigned N = sizeof(du_int) * CHAR_BIT;
33     int sd = N - __builtin_clzll(a);  /* number of significant digits */
34     int e = sd - 1;             /* 8 exponent */
35     if (sd > FLT_MANT_DIG)
36     {
37         /*  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
38          *  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
39          *                                                12345678901234567890123456
40          *  1 = msb 1 bit
41          *  P = bit FLT_MANT_DIG-1 bits to the right of 1
42          *  Q = bit FLT_MANT_DIG bits to the right of 1
43          *  R = "or" of all bits to the right of Q
44          */
45         switch (sd)
46         {
47         case FLT_MANT_DIG + 1:
48             a <<= 1;
49             break;
50         case FLT_MANT_DIG + 2:
51             break;
52         default:
53             a = (a >> (sd - (FLT_MANT_DIG+2))) |
54                 ((a & ((du_int)(-1) >> ((N + FLT_MANT_DIG+2) - sd))) != 0);
55         };
56         /* finish: */
57         a |= (a & 4) != 0;  /* Or P into R */
58         ++a;  /* round - this step may add a significant bit */
59         a >>= 2;  /* dump Q and R */
60         /* a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits */
61         if (a & ((du_int)1 << FLT_MANT_DIG))
62         {
63             a >>= 1;
64             ++e;
65         }
66         /* a is now rounded to FLT_MANT_DIG bits */
67     }
68     else
69     {
70         a <<= (FLT_MANT_DIG - sd);
71         /* a is now rounded to FLT_MANT_DIG bits */
72     }
73     float_bits fb;
74     fb.u = ((e + 127) << 23)       |  /* exponent */
75            ((su_int)a & 0x007FFFFF);  /* mantissa */
76     return fb.f;
77 }
78