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 */