1 /* ===-- floatundidf.c - Implement __floatundidf ---------------------------===
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 __floatundidf for the compiler_rt library.
12 * ===----------------------------------------------------------------------===
15 /* Returns: convert a to a double, rounding toward even. */
17 /* Assumption: double is a IEEE 64 bit floating point type
18 * du_int is a 64 bit integral type
21 /* seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm */
25 ARM_EABI_FNALIAS(ul2d, floatundidf)
28 /* Support for systems that have hardware floating-point; we'll set the inexact flag
29 * as a side-effect of this computation.
32 COMPILER_RT_ABI double
33 __floatundidf(du_int a)
35 static const double twop52 = 4503599627370496.0; // 0x1.0p52
36 static const double twop84 = 19342813113834066795298816.0; // 0x1.0p84
37 static const double twop84_plus_twop52 = 19342813118337666422669312.0; // 0x1.00000001p84
39 union { uint64_t x; double d; } high = { .d = twop84 };
40 union { uint64_t x; double d; } low = { .d = twop52 };
43 low.x |= a & UINT64_C(0x00000000ffffffff);
45 const double result = (high.d - twop84_plus_twop52) + low.d;
50 /* Support for systems that don't have hardware floating-point; there are no flags to
51 * set, and we don't want to code-gen to an unknown soft-float implementation.
54 COMPILER_RT_ABI double
55 __floatundidf(du_int a)
59 const unsigned N = sizeof(du_int) * CHAR_BIT;
60 int sd = N - __builtin_clzll(a); /* number of significant digits */
61 int e = sd - 1; /* exponent */
62 if (sd > DBL_MANT_DIG)
64 /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
65 * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
66 * 12345678901234567890123456
68 * P = bit DBL_MANT_DIG-1 bits to the right of 1
69 * Q = bit DBL_MANT_DIG bits to the right of 1
70 * R = "or" of all bits to the right of Q
74 case DBL_MANT_DIG + 1:
77 case DBL_MANT_DIG + 2:
80 a = (a >> (sd - (DBL_MANT_DIG+2))) |
81 ((a & ((du_int)(-1) >> ((N + DBL_MANT_DIG+2) - sd))) != 0);
84 a |= (a & 4) != 0; /* Or P into R */
85 ++a; /* round - this step may add a significant bit */
86 a >>= 2; /* dump Q and R */
87 /* a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits */
88 if (a & ((du_int)1 << DBL_MANT_DIG))
93 /* a is now rounded to DBL_MANT_DIG bits */
97 a <<= (DBL_MANT_DIG - sd);
98 /* a is now rounded to DBL_MANT_DIG bits */
101 fb.u.high = ((e + 1023) << 20) | /* exponent */
102 ((su_int)(a >> 32) & 0x000FFFFF); /* mantissa-high */
103 fb.u.low = (su_int)a; /* mantissa-low */