xref: /external/compiler-rt/lib/builtins/fixdfsi.c

//===-- lib/fixdfsi.c - Double-precision -> integer conversion ----*- C -*-===//
//
//                     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 double-precision to integer conversion for the
// compiler-rt library.  No range checking is performed; the behavior of this
// conversion is undefined for out of range values in the C standard.
//
//===----------------------------------------------------------------------===//

#define DOUBLE_PRECISION
#include "fp_lib.h"

#include "int_lib.h"

ARM_EABI_FNALIAS(d2iz, fixdfsi)

COMPILER_RT_ABI int
__fixdfsi(fp_t a) {

    // Break a into sign, exponent, significand
    const rep_t aRep = toRep(a);
    const rep_t aAbs = aRep & absMask;
    const int sign = aRep & signBit ? -1 : 1;
    const int exponent = (aAbs >> significandBits) - exponentBias;
    const rep_t significand = (aAbs & significandMask) | implicitBit;

    // If 0 < exponent < significandBits, right shift to get the result.
    if ((unsigned int)exponent < significandBits) {
        return sign * (significand >> (significandBits - exponent));
    }

    // If exponent is negative, the result is zero.
    else if (exponent < 0) {
        return 0;
    }

    // If significandBits < exponent, left shift to get the result.  This shift
    // may end up being larger than the type width, which incurs undefined
    // behavior, but the conversion itself is undefined in that case, so
    // whatever the compiler decides to do is fine.
    else {
        return sign * (significand << (exponent - significandBits));
    }
}