llvm-project/compiler-rt/lib/builtins/fixxfti.c

/* ===-- fixxfti.c - Implement __fixxfti -----------------------------------===
 *
 * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 * See https://llvm.org/LICENSE.txt for license information.
 * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 *
 * ===----------------------------------------------------------------------===
 *
 * This file implements __fixxfti for the compiler_rt library.
 *
 * ===----------------------------------------------------------------------===
 */

#include "int_lib.h"

#ifdef CRT_HAS_128BIT

/* Returns: convert a to a signed long long, rounding toward zero. */

/* Assumption: long double is an intel 80 bit floating point type padded with 6 bytes
 *             ti_int is a 128 bit integral type
 *             value in long double is representable in ti_int
 */

/* 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
 */

COMPILER_RT_ABI ti_int
__fixxfti(long double a)
{
    const ti_int ti_max = (ti_int)((~(tu_int)0) / 2);
    const ti_int ti_min = -ti_max - 1;
    long_double_bits fb;
    fb.f = a;
    int e = (fb.u.high.s.low & 0x00007FFF) - 16383;
    if (e < 0)
        return 0;
    ti_int s = -(si_int)((fb.u.high.s.low & 0x00008000) >> 15);
    ti_int r = fb.u.low.all;
    if ((unsigned)e >= sizeof(ti_int) * CHAR_BIT)
        return a > 0 ? ti_max : ti_min;
    if (e > 63)
        r <<= (e - 63);
    else
        r >>= (63 - e);
    return (r ^ s) - s;
}

#endif /* CRT_HAS_128BIT */