1 /* ===-- floatuntidf.c - Implement __floatuntidf ---------------------------===
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 __floatuntidf for the compiler_rt library.
12 * ===----------------------------------------------------------------------===
19 /* Returns: convert a to a double, rounding toward even. */
21 /* Assumption: double is a IEEE 64 bit floating point type
22 * tu_int is a 128 bit integral type
25 /* seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm */
27 COMPILER_RT_ABI
double
28 __floatuntidf(tu_int a
)
32 const unsigned N
= sizeof(tu_int
) * CHAR_BIT
;
33 int sd
= N
- __clzti2(a
); /* number of significant digits */
34 int e
= sd
- 1; /* exponent */
35 if (sd
> DBL_MANT_DIG
)
37 /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
38 * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
39 * 12345678901234567890123456
41 * P = bit DBL_MANT_DIG-1 bits to the right of 1
42 * Q = bit DBL_MANT_DIG bits to the right of 1
43 * R = "or" of all bits to the right of Q
47 case DBL_MANT_DIG
+ 1:
50 case DBL_MANT_DIG
+ 2:
53 a
= (a
>> (sd
- (DBL_MANT_DIG
+2))) |
54 ((a
& ((tu_int
)(-1) >> ((N
+ DBL_MANT_DIG
+2) - sd
))) != 0);
57 a
|= (a
& 4) != 0; /* Or P into R */
58 ++a
; /* round - this step may add a significant bit */
59 a
>>= 2; /* dump Q and R */
60 /* a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits */
61 if (a
& ((tu_int
)1 << DBL_MANT_DIG
))
66 /* a is now rounded to DBL_MANT_DIG bits */
70 a
<<= (DBL_MANT_DIG
- sd
);
71 /* a is now rounded to DBL_MANT_DIG bits */
74 fb
.u
.s
.high
= ((e
+ 1023) << 20) | /* exponent */
75 ((su_int
)(a
>> 32) & 0x000FFFFF); /* mantissa-high */
76 fb
.u
.s
.low
= (su_int
)a
; /* mantissa-low */
80 #endif /* CRT_HAS_128BIT */