runtime/lib/floatdixf.c

/* ===-- floatdixf.c - Implement __floatdixf -------------------------------===
 *
 *                     The LLVM Compiler Infrastructure
 *
 * This file is distributed under the University of Illinois Open Source
 * License. See LICENSE.TXT for details.
 *
 * ===----------------------------------------------------------------------===
 *
 * This file implements __floatdixf for the compiler_rt library.
 *
 * ===----------------------------------------------------------------------===
 */ 

#if !_ARCH_PPC

#include "int_lib.h"

/* Returns: convert a to a long double, rounding toward even. */

/* Assumption: long double is a IEEE 80 bit floating point type padded to 128 bits
 *             di_int is a 64 bit integral type
 */

/* gggg gggg gggg gggg gggg gggg gggg gggg | gggg gggg gggg gggg seee eeee eeee eeee |
 * 1mmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm
 */

long double
__floatdixf(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 clz = __builtin_clzll(a);
    int e = (N - 1) - clz ;    /* exponent */
    long_double_bits fb;
    fb.u.high.s.low = ((su_int)s & 0x00008000) |  /* sign */
		      (e + 16383);                /* exponent */
    fb.u.low.all = a << clz;                    /* mantissa */
    return fb.f;
}

#endif /* !_ARCH_PPC */