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/* ===-- floatundidf.c - Implement __floatundidf ---------------------------===
*
* Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
* See https://llvm.org/LICENSE.txt for license information.
* SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
*
* ===----------------------------------------------------------------------===
*
* This file implements __floatundidf for the compiler_rt library.
*
* ===----------------------------------------------------------------------===
*/
/* Returns: convert a to a double, rounding toward even. */
/* Assumption: double is a IEEE 64 bit floating point type
* du_int is a 64 bit integral type
*/
/* seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm
* mmmm */
#include "int_lib.h"
#ifndef __SOFT_FP__
/* Support for systems that have hardware floating-point; we'll set the inexact
* flag as a side-effect of this computation.
*/
COMPILER_RT_ABI double __floatundidf(du_int a) {
static const double twop52 = 4503599627370496.0; // 0x1.0p52
static const double twop84 = 19342813113834066795298816.0; // 0x1.0p84
static const double twop84_plus_twop52 =
19342813118337666422669312.0; // 0x1.00000001p84
union {
uint64_t x;
double d;
} high = {.d = twop84};
union {
uint64_t x;
double d;
} low = {.d = twop52};
high.x |= a >> 32;
low.x |= a & UINT64_C(0x00000000ffffffff);
const double result = (high.d - twop84_plus_twop52) + low.d;
return result;
}
#else
/* Support for systems that don't have hardware floating-point; there are no
* flags to set, and we don't want to code-gen to an unknown soft-float
* implementation.
*/
COMPILER_RT_ABI double __floatundidf(du_int a) {
if (a == 0)
return 0.0;
const unsigned N = sizeof(du_int) * CHAR_BIT;
int sd = N - __builtin_clzll(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 & ((du_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 & ((du_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
#if defined(__ARM_EABI__)
#if defined(COMPILER_RT_ARMHF_TARGET)
AEABI_RTABI double __aeabi_ul2d(du_int a) { return __floatundidf(a); }
#else
AEABI_RTABI double __aeabi_ul2d(du_int a) COMPILER_RT_ALIAS(__floatundidf);
#endif
#endif
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