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/* ===-- floattixf.c - Implement __floattixf -------------------------------===
*
* The LLVM Compiler Infrastructure
*
* This file is distributed under the University of Illinois Open Source
* License. See LICENSE.TXT for details.
*
* ===----------------------------------------------------------------------===
*
* This file implements __floattixf for the compiler_rt library.
*
* ===----------------------------------------------------------------------===
*/
#if __x86_64
#include "int_lib.h"
#include <float.h>
/* 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
* ti_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
__floattixf(ti_int a)
{
if (a == 0)
return 0.0;
const unsigned N = sizeof(ti_int) * CHAR_BIT;
const ti_int s = a >> (N-1);
a = (a ^ s) - s;
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 = ((tu_int)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.low = ((su_int)s & 0x8000) | /* sign */
(e + 16383); /* exponent */
fb.u.low.all = (du_int)a; /* mantissa */
return fb.f;
}
#endif
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