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/*===-- floatdisf.c - Implement __floatdisf -------------------------------===
*
* 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 __floatdisf for the compiler_rt library.
*
*===----------------------------------------------------------------------===
*/
#include "int_lib.h"
#include <float.h>
/* Returns: convert a to a float, rounding toward even.*/
/* Assumption: float is a IEEE 32 bit floating point type
* di_int is a 64 bit integral type
*/
/* seee eeee emmm mmmm mmmm mmmm mmmm mmmm */
float
__floatdisf(di_int a)
{
if (a == 0)
return 0.0F;
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 > 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 = ((du_int)a >> (sd - (FLT_MANT_DIG+2))) |
((a & ((du_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 & ((du_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 = ((su_int)s & 0x80000000) | /* sign */
((e + 127) << 23) | /* exponent */
((su_int)a & 0x007FFFFF); /* mantissa */
return fb.f;
}
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