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1 /*===-- floatdisf.c - Implement __floatdisf -------------------------------===
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 __floatdisf 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  *             di_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(l2f,floatdisf)25 ARM_EABI_FNALIAS(l2f, floatdisf)
26 
27 COMPILER_RT_ABI float
28 __floatdisf(di_int a)
29 {
30     if (a == 0)
31         return 0.0F;
32     const unsigned N = sizeof(di_int) * CHAR_BIT;
33     const di_int s = a >> (N-1);
34     a = (a ^ s) - s;
35     int sd = N - __builtin_clzll(a);  /* number of significant digits */
36     int e = sd - 1;             /* exponent */
37     if (sd > FLT_MANT_DIG)
38     {
39         /*  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
40          *  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
41          *                                                12345678901234567890123456
42          *  1 = msb 1 bit
43          *  P = bit FLT_MANT_DIG-1 bits to the right of 1
44          *  Q = bit FLT_MANT_DIG bits to the right of 1
45          *  R = "or" of all bits to the right of Q
46          */
47         switch (sd)
48         {
49         case FLT_MANT_DIG + 1:
50             a <<= 1;
51             break;
52         case FLT_MANT_DIG + 2:
53             break;
54         default:
55             a = ((du_int)a >> (sd - (FLT_MANT_DIG+2))) |
56                 ((a & ((du_int)(-1) >> ((N + FLT_MANT_DIG+2) - sd))) != 0);
57         };
58         /* finish: */
59         a |= (a & 4) != 0;  /* Or P into R */
60         ++a;  /* round - this step may add a significant bit */
61         a >>= 2;  /* dump Q and R */
62         /* a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits */
63         if (a & ((du_int)1 << FLT_MANT_DIG))
64         {
65             a >>= 1;
66             ++e;
67         }
68         /* a is now rounded to FLT_MANT_DIG bits */
69     }
70     else
71     {
72         a <<= (FLT_MANT_DIG - sd);
73         /* a is now rounded to FLT_MANT_DIG bits */
74     }
75     float_bits fb;
76     fb.u = ((su_int)s & 0x80000000) |  /* sign */
77            ((e + 127) << 23)       |  /* exponent */
78            ((su_int)a & 0x007FFFFF);   /* mantissa */
79     return fb.f;
80 }
81