1 //===-- floatundisf.c - Implement __floatundisf ---------------------------===//
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 __floatundisf for the compiler_rt library.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 // Returns: convert a to a float, rounding toward even.
14 
15 // Assumption: float is a IEEE 32 bit floating point type
16 //            du_int is a 64 bit integral type
17 
18 // seee eeee emmm mmmm mmmm mmmm mmmm mmmm
19 
20 #include "int_lib.h"
21 
__floatundisf(du_int a)22 COMPILER_RT_ABI float __floatundisf(du_int a) {
23   if (a == 0)
24     return 0.0F;
25   const unsigned N = sizeof(du_int) * CHAR_BIT;
26   int sd = N - __builtin_clzll(a); // number of significant digits
27   si_int e = sd - 1;               // 8 exponent
28   if (sd > FLT_MANT_DIG) {
29     //  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
30     //  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
31     //                                                12345678901234567890123456
32     //  1 = msb 1 bit
33     //  P = bit FLT_MANT_DIG-1 bits to the right of 1
34     //  Q = bit FLT_MANT_DIG bits to the right of 1
35     //  R = "or" of all bits to the right of Q
36     switch (sd) {
37     case FLT_MANT_DIG + 1:
38       a <<= 1;
39       break;
40     case FLT_MANT_DIG + 2:
41       break;
42     default:
43       a = (a >> (sd - (FLT_MANT_DIG + 2))) |
44           ((a & ((du_int)(-1) >> ((N + FLT_MANT_DIG + 2) - sd))) != 0);
45     };
46     // finish:
47     a |= (a & 4) != 0; // Or P into R
48     ++a;               // round - this step may add a significant bit
49     a >>= 2;           // dump Q and R
50     // a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits
51     if (a & ((du_int)1 << FLT_MANT_DIG)) {
52       a >>= 1;
53       ++e;
54     }
55     // a is now rounded to FLT_MANT_DIG bits
56   } else {
57     a <<= (FLT_MANT_DIG - sd);
58     // a is now rounded to FLT_MANT_DIG bits
59   }
60   float_bits fb;
61   fb.u = ((e + 127) << 23) |       // exponent
62          ((su_int)a & 0x007FFFFF); // mantissa
63   return fb.f;
64 }
65 
66 #if defined(__ARM_EABI__)
67 #if defined(COMPILER_RT_ARMHF_TARGET)
__aeabi_ul2f(du_int a)68 AEABI_RTABI float __aeabi_ul2f(du_int a) { return __floatundisf(a); }
69 #else
70 COMPILER_RT_ALIAS(__floatundisf, __aeabi_ul2f)
71 #endif
72 #endif
73