1 /* ===-- floatuntixf.c - Implement __floatuntixf ---------------------------===
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 __floatuntixf for the compiler_rt library.
12 * ===----------------------------------------------------------------------===
19 /* Returns: convert a to a long double, rounding toward even. */
21 /* Assumption: long double is a IEEE 80 bit floating point type padded to 128 bits
22 * tu_int is a 128 bit integral type
25 /* gggg gggg gggg gggg gggg gggg gggg gggg | gggg gggg gggg gggg seee eeee eeee eeee |
26 * 1mmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm
29 si_int __clzti2(ti_int a);
32 __floatuntixf(tu_int a)
36 const unsigned N = sizeof(tu_int) * CHAR_BIT;
37 int sd = N - __clzti2(a); /* number of significant digits */
38 int e = sd - 1; /* exponent */
39 if (sd > LDBL_MANT_DIG)
41 /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
42 * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
43 * 12345678901234567890123456
45 * P = bit LDBL_MANT_DIG-1 bits to the right of 1
46 * Q = bit LDBL_MANT_DIG bits to the right of 1
47 * R = "or" of all bits to the right of Q
51 case LDBL_MANT_DIG + 1:
54 case LDBL_MANT_DIG + 2:
57 a = (a >> (sd - (LDBL_MANT_DIG+2))) |
58 ((a & ((tu_int)(-1) >> ((N + LDBL_MANT_DIG+2) - sd))) != 0);
61 a |= (a & 4) != 0; /* Or P into R */
62 ++a; /* round - this step may add a significant bit */
63 a >>= 2; /* dump Q and R */
64 /* a is now rounded to LDBL_MANT_DIG or LDBL_MANT_DIG+1 bits */
65 if (a & ((tu_int)1 << LDBL_MANT_DIG))
70 /* a is now rounded to LDBL_MANT_DIG bits */
74 a <<= (LDBL_MANT_DIG - sd);
75 /* a is now rounded to LDBL_MANT_DIG bits */
78 fb.u.high.s.low = (e + 16383); /* exponent */
79 fb.u.low.all = (du_int)a; /* mantissa */