runtime/lib/fixunsxfti.c

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

#if __x86_64

#include "int_lib.h"

/* Returns: convert a to a unsigned long long, rounding toward zero.
 *          Negative values all become zero.
 */

/* Assumption: long double is an intel 80 bit floating point type padded with 6 bytes
 *             tu_int is a 64 bit integral type
 *             value in long double is representable in tu_int or is negative 
 *                 (no range checking performed)
 */

/* 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
 */

tu_int
__fixunsxfti(long double a)
{
    long_double_bits fb;
    fb.f = a;
    int e = (fb.u.high.s.low & 0x00007FFF) - 16383;
    if (e < 0 || (fb.u.high.s.low & 0x00008000))
        return 0;
    tu_int r = fb.u.low.all;
    if (e > 63)
        r <<= (e - 63);
    else
        r >>= (63 - e);
    return r;
}

#endif