83 lines
2.5 KiB
C
83 lines
2.5 KiB
C
/* clang-format off */
|
|
/* ===-- floatuntisf.c - Implement __floatuntisf ---------------------------===
|
|
*
|
|
* 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 __floatuntisf for the compiler_rt library.
|
|
*
|
|
* ===----------------------------------------------------------------------===
|
|
*/
|
|
|
|
STATIC_YOINK("huge_compiler_rt_license");
|
|
|
|
#include "third_party/compiler_rt/int_lib.h"
|
|
|
|
#ifdef CRT_HAS_128BIT
|
|
|
|
/* Returns: convert a to a float, rounding toward even. */
|
|
|
|
/* Assumption: float is a IEEE 32 bit floating point type
|
|
* tu_int is a 128 bit integral type
|
|
*/
|
|
|
|
/* seee eeee emmm mmmm mmmm mmmm mmmm mmmm */
|
|
|
|
COMPILER_RT_ABI float
|
|
__floatuntisf(tu_int a)
|
|
{
|
|
if (a == 0)
|
|
return 0.0F;
|
|
const unsigned N = sizeof(tu_int) * CHAR_BIT;
|
|
int sd = N - __clzti2(a); /* number of significant digits */
|
|
int e = sd - 1; /* exponent */
|
|
if (sd > FLT_MANT_DIG)
|
|
{
|
|
/* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
|
|
* finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
|
|
* 12345678901234567890123456
|
|
* 1 = msb 1 bit
|
|
* P = bit FLT_MANT_DIG-1 bits to the right of 1
|
|
* Q = bit FLT_MANT_DIG bits to the right of 1
|
|
* R = "or" of all bits to the right of Q
|
|
*/
|
|
switch (sd)
|
|
{
|
|
case FLT_MANT_DIG + 1:
|
|
a <<= 1;
|
|
break;
|
|
case FLT_MANT_DIG + 2:
|
|
break;
|
|
default:
|
|
a = (a >> (sd - (FLT_MANT_DIG+2))) |
|
|
((a & ((tu_int)(-1) >> ((N + FLT_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 FLT_MANT_DIG or FLT_MANT_DIG+1 bits */
|
|
if (a & ((tu_int)1 << FLT_MANT_DIG))
|
|
{
|
|
a >>= 1;
|
|
++e;
|
|
}
|
|
/* a is now rounded to FLT_MANT_DIG bits */
|
|
}
|
|
else
|
|
{
|
|
a <<= (FLT_MANT_DIG - sd);
|
|
/* a is now rounded to FLT_MANT_DIG bits */
|
|
}
|
|
float_bits fb;
|
|
fb.u = ((e + 127) << 23) | /* exponent */
|
|
((su_int)a & 0x007FFFFF); /* mantissa */
|
|
return fb.f;
|
|
}
|
|
|
|
#endif /* CRT_HAS_128BIT */
|