1 //===-- floatdisf.c - Implement __floatdisf -------------------------------===//
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 __floatdisf for the compiler_rt library.
11 //===----------------------------------------------------------------------===//
13 // Returns: convert a to a float, rounding toward even.
15 // Assumption: float is a IEEE 32 bit floating point type
16 // di_int is a 64 bit integral type
18 // seee eeee emmm mmmm mmmm mmmm mmmm mmmm
22 COMPILER_RT_ABI float __floatdisf(di_int a) {
25 const unsigned N = sizeof(di_int) * CHAR_BIT;
26 const di_int s = a >> (N - 1);
28 int sd = N - __builtin_clzll(a); // number of significant digits
29 int e = sd - 1; // exponent
30 if (sd > FLT_MANT_DIG) {
31 // start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
32 // finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
33 // 12345678901234567890123456
35 // P = bit FLT_MANT_DIG-1 bits to the right of 1
36 // Q = bit FLT_MANT_DIG bits to the right of 1
37 // R = "or" of all bits to the right of Q
39 case FLT_MANT_DIG + 1:
42 case FLT_MANT_DIG + 2:
45 a = ((du_int)a >> (sd - (FLT_MANT_DIG + 2))) |
46 ((a & ((du_int)(-1) >> ((N + FLT_MANT_DIG + 2) - sd))) != 0);
49 a |= (a & 4) != 0; // Or P into R
50 ++a; // round - this step may add a significant bit
51 a >>= 2; // dump Q and R
52 // a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits
53 if (a & ((du_int)1 << FLT_MANT_DIG)) {
57 // a is now rounded to FLT_MANT_DIG bits
59 a <<= (FLT_MANT_DIG - sd);
60 // a is now rounded to FLT_MANT_DIG bits
63 fb.u = ((su_int)s & 0x80000000) | // sign
64 ((e + 127) << 23) | // exponent
65 ((su_int)a & 0x007FFFFF); // mantissa
69 #if defined(__ARM_EABI__)
70 #if defined(COMPILER_RT_ARMHF_TARGET)
71 AEABI_RTABI float __aeabi_l2f(di_int a) { return __floatdisf(a); }
73 COMPILER_RT_ALIAS(__floatdisf, __aeabi_l2f)