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/* ===-- floatuntidf.c - Implement __floatuntidf ---------------------------===
*
* The LLVM Compiler Infrastructure
*
* This file is dual licensed under the MIT and the University of Illinois Open
* Source Licenses. See LICENSE.TXT for details.
*
* ===----------------------------------------------------------------------===
*
* This file implements __floatuntidf for the compiler_rt library.
*
* ===----------------------------------------------------------------------===
*/
#include "int_lib.h"
#ifdef CRT_HAS_128BIT
/* Returns: convert a to a double, rounding toward even. */
/* Assumption: double is a IEEE 64 bit floating point type
* tu_int is a 128 bit integral type
*/
/* seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm */
COMPILER_RT_ABI double
__floatuntidf(tu_int a)
{
if (a == 0)
return 0.0;
const unsigned N = sizeof(tu_int) * CHAR_BIT;
int sd = N - __clzti2(a); /* number of significant digits */
int e = sd - 1; /* exponent */
if (sd > DBL_MANT_DIG)
{
/* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
* finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
* 12345678901234567890123456
* 1 = msb 1 bit
* P = bit DBL_MANT_DIG-1 bits to the right of 1
* Q = bit DBL_MANT_DIG bits to the right of 1
* R = "or" of all bits to the right of Q
*/
switch (sd)
{
case DBL_MANT_DIG + 1:
a <<= 1;
break;
case DBL_MANT_DIG + 2:
break;
default:
a = (a >> (sd - (DBL_MANT_DIG+2))) |
((a & ((tu_int)(-1) >> ((N + DBL_MANT_DIG+2) - sd))) != 0);
};
/* finish: */
a |= (a & 4) != 0; /* Or P into R */
++a; /* round - this step may add a significant bit */
a >>= 2; /* dump Q and R */
/* a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits */
if (a & ((tu_int)1 << DBL_MANT_DIG))
{
a >>= 1;
++e;
}
/* a is now rounded to DBL_MANT_DIG bits */
}
else
{
a <<= (DBL_MANT_DIG - sd);
/* a is now rounded to DBL_MANT_DIG bits */
}
double_bits fb;
fb.u.s.high = ((e + 1023) << 20) | /* exponent */
((su_int)(a >> 32) & 0x000FFFFF); /* mantissa-high */
fb.u.s.low = (su_int)a; /* mantissa-low */
return fb.f;
}
#endif /* CRT_HAS_128BIT */
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