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/* ===-- floatuntixf.c - Implement __floatuntixf ---------------------------===
*
* 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 __floatuntixf for the compiler_rt library.
*
* ===----------------------------------------------------------------------===
*/
#include "int_lib.h"
#if __x86_64
/* Returns: convert a to a long double, rounding toward even. */
/* Assumption: long double is a IEEE 80 bit floating point type padded to 128 bits
* tu_int is a 128 bit integral type
*/
/* gggg gggg gggg gggg gggg gggg gggg gggg | gggg gggg gggg gggg seee eeee eeee eeee |
* 1mmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm
*/
si_int __clzti2(ti_int a);
long double
__floatuntixf(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 > LDBL_MANT_DIG)
{
/* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
* finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
* 12345678901234567890123456
* 1 = msb 1 bit
* P = bit LDBL_MANT_DIG-1 bits to the right of 1
* Q = bit LDBL_MANT_DIG bits to the right of 1
* R = "or" of all bits to the right of Q
*/
switch (sd)
{
case LDBL_MANT_DIG + 1:
a <<= 1;
break;
case LDBL_MANT_DIG + 2:
break;
default:
a = (a >> (sd - (LDBL_MANT_DIG+2))) |
((a & ((tu_int)(-1) >> ((N + LDBL_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 LDBL_MANT_DIG or LDBL_MANT_DIG+1 bits */
if (a & ((tu_int)1 << LDBL_MANT_DIG))
{
a >>= 1;
++e;
}
/* a is now rounded to LDBL_MANT_DIG bits */
}
else
{
a <<= (LDBL_MANT_DIG - sd);
/* a is now rounded to LDBL_MANT_DIG bits */
}
long_double_bits fb;
fb.u.high.s.low = (e + 16383); /* exponent */
fb.u.low.all = (du_int)a; /* mantissa */
return fb.f;
}
#endif
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