1 /* ===-- floattixf.c - Implement __floattixf -------------------------------===
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 __floattixf for the compiler_rt library.
12 * ===----------------------------------------------------------------------===
20 /* Returns: convert a to a long double, rounding toward even. */
22 /* Assumption: long double is a IEEE 80 bit floating point type padded to 128 bits
23 * ti_int is a 128 bit integral type
26 /* gggg gggg gggg gggg gggg gggg gggg gggg | gggg gggg gggg gggg seee eeee eeee eeee |
27 * 1mmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm
30 si_int __clzti2(ti_int a);
37 const unsigned N = sizeof(ti_int) * CHAR_BIT;
38 const ti_int s = a >> (N-1);
40 int sd = N - __clzti2(a); /* number of significant digits */
41 int e = sd - 1; /* exponent */
42 if (sd > LDBL_MANT_DIG)
44 /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
45 * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
46 * 12345678901234567890123456
48 * P = bit LDBL_MANT_DIG-1 bits to the right of 1
49 * Q = bit LDBL_MANT_DIG bits to the right of 1
50 * R = "or" of all bits to the right of Q
54 case LDBL_MANT_DIG + 1:
57 case LDBL_MANT_DIG + 2:
60 a = ((tu_int)a >> (sd - (LDBL_MANT_DIG+2))) |
61 ((a & ((tu_int)(-1) >> ((N + LDBL_MANT_DIG+2) - sd))) != 0);
64 a |= (a & 4) != 0; /* Or P into R */
65 ++a; /* round - this step may add a significant bit */
66 a >>= 2; /* dump Q and R */
67 /* a is now rounded to LDBL_MANT_DIG or LDBL_MANT_DIG+1 bits */
68 if (a & ((tu_int)1 << LDBL_MANT_DIG))
73 /* a is now rounded to LDBL_MANT_DIG bits */
77 a <<= (LDBL_MANT_DIG - sd);
78 /* a is now rounded to LDBL_MANT_DIG bits */
81 fb.u.high.s.low = ((su_int)s & 0x8000) | /* sign */
82 (e + 16383); /* exponent */
83 fb.u.low.all = (du_int)a; /* mantissa */