1 //===-- floattisf.c - Implement __floattisf -------------------------------===//
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
7 //===----------------------------------------------------------------------===//
9 // This file implements __floattisf for the compiler_rt library.
11 //===----------------------------------------------------------------------===//
17 // Returns: convert a to a float, rounding toward even.
19 // Assumption: float is a IEEE 32 bit floating point type
20 // ti_int is a 128 bit integral type
22 // seee eeee emmm mmmm mmmm mmmm mmmm mmmm
24 COMPILER_RT_ABI float __floattisf(ti_int a) {
27 const unsigned N = sizeof(ti_int) * CHAR_BIT;
28 const ti_int s = a >> (N - 1);
30 int sd = N - __clzti2(a); // number of significant digits
31 int e = sd - 1; // exponent
32 if (sd > FLT_MANT_DIG) {
33 // start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
34 // finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
35 // 12345678901234567890123456
37 // P = bit FLT_MANT_DIG-1 bits to the right of 1
38 // Q = bit FLT_MANT_DIG bits to the right of 1
39 // R = "or" of all bits to the right of Q
41 case FLT_MANT_DIG + 1:
44 case FLT_MANT_DIG + 2:
47 a = ((tu_int)a >> (sd - (FLT_MANT_DIG + 2))) |
48 ((a & ((tu_int)(-1) >> ((N + FLT_MANT_DIG + 2) - sd))) != 0);
51 a |= (a & 4) != 0; // Or P into R
52 ++a; // round - this step may add a significant bit
53 a >>= 2; // dump Q and R
54 // a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits
55 if (a & ((tu_int)1 << FLT_MANT_DIG)) {
59 // a is now rounded to FLT_MANT_DIG bits
61 a <<= (FLT_MANT_DIG - sd);
62 // a is now rounded to FLT_MANT_DIG bits
65 fb.u = ((su_int)s & 0x80000000) | // sign
66 ((e + 127) << 23) | // exponent
67 ((su_int)a & 0x007FFFFF); // mantissa
71 #endif // CRT_HAS_128BIT