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Justine Tunney 2020-06-15 07:18:57 -07:00
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third_party/compiler_rt/floatdidf.c vendored Normal file
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/* clang-format off */
/*===-- floatdidf.c - Implement __floatdidf -------------------------------===
*
* 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 __floatdidf for the compiler_rt library.
*
*===----------------------------------------------------------------------===
*/
STATIC_YOINK("huge_compiler_rt_license");
#include "libc/literal.h"
#include "third_party/compiler_rt/int_lib.h"
/* Returns: convert a to a double, rounding toward even. */
/* Assumption: double is a IEEE 64 bit floating point type
* di_int is a 64 bit integral type
*/
/* seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm */
#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
__floatdidf(di_int a)
{
static const double twop52 = 4503599627370496.0; // 0x1.0p52
static const double twop32 = 4294967296.0; // 0x1.0p32
union { int64_t x; double d; } low = { .d = twop52 };
const double high = (int32_t)(a >> 32) * twop32;
low.x |= a & INT64_C(0x00000000ffffffff);
const double result = (high - 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
__floatdidf(di_int a)
{
if (a == 0)
return 0.0;
const unsigned N = sizeof(di_int) * CHAR_BIT;
const di_int s = a >> (N-1);
a = (a ^ s) - s;
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 = ((du_int)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 = ((su_int)s & 0x80000000) | /* sign */
((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_l2d(di_int a) {
return __floatdidf(a);
}
#else
AEABI_RTABI double __aeabi_l2d(di_int a) COMPILER_RT_ALIAS(__floatdidf);
#endif
#endif