1 /*===-- floatundisf.c - Implement __floatundisf ---------------------------===
3 * The LLVM Compiler Infrastructure
5 * This file is dual licensed under the MIT and the University of Illinois Open
6 * Source Licenses. See LICENSE.TXT for details.
8 * ===----------------------------------------------------------------------===
10 * This file implements __floatundisf for the compiler_rt library.
12 *===----------------------------------------------------------------------===
18 /* Returns: convert a to a float, rounding toward even. */
20 /* Assumption: float is a IEEE 32 bit floating point type
21 * du_int is a 64 bit integral type
24 /* seee eeee emmm mmmm mmmm mmmm mmmm mmmm */
28 ARM_EABI_FNALIAS(ul2f, floatundisf);
31 __floatundisf(du_int a)
35 const unsigned N = sizeof(du_int) * CHAR_BIT;
36 int sd = N - __builtin_clzll(a); /* number of significant digits */
37 int e = sd - 1; /* 8 exponent */
38 if (sd > FLT_MANT_DIG)
40 /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
41 * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
42 * 12345678901234567890123456
44 * P = bit FLT_MANT_DIG-1 bits to the right of 1
45 * Q = bit FLT_MANT_DIG bits to the right of 1
46 * R = "or" of all bits to the right of Q
50 case FLT_MANT_DIG + 1:
53 case FLT_MANT_DIG + 2:
56 a = (a >> (sd - (FLT_MANT_DIG+2))) |
57 ((a & ((du_int)(-1) >> ((N + FLT_MANT_DIG+2) - sd))) != 0);
60 a |= (a & 4) != 0; /* Or P into R */
61 ++a; /* round - this step may add a significant bit */
62 a >>= 2; /* dump Q and R */
63 /* a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits */
64 if (a & ((du_int)1 << FLT_MANT_DIG))
69 /* a is now rounded to FLT_MANT_DIG bits */
73 a <<= (FLT_MANT_DIG - sd);
74 /* a is now rounded to FLT_MANT_DIG bits */
77 fb.u = ((e + 127) << 23) | /* exponent */
78 ((su_int)a & 0x007FFFFF); /* mantissa */