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//===-- lib/floattitf.c - int128 -> quad-precision conversion -----*- C -*-===//
//
// 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 ti_int to quad-precision conversion for the
// compiler-rt library in the IEEE-754 default round-to-nearest, ties-to-even
// mode.
//
//===----------------------------------------------------------------------===//
#define QUAD_PRECISION
#include "fp_lib.h"
#include "int_lib.h"
/* Returns: convert a ti_int to a fp_t, rounding toward even. */
/* Assumption: fp_t is a IEEE 128 bit floating point type
* ti_int is a 128 bit integral type
*/
/* seee eeee eeee eeee mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm |
* mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm
*/
#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
COMPILER_RT_ABI fp_t
__floattitf(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.all = (s & 0x8000000000000000LL) /* sign */
| (du_int)(e + 16383) << 48 /* exponent */
| ((a >> 64) & 0x0000ffffffffffffLL); /* significand */
fb.u.low.all = (du_int)(a);
return fb.f;
}
#endif
|
