lib/builtins/fixdfsi.c

   1 //===-- lib/fixdfsi.c - Double-precision -> integer conversion ----*- C -*-===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is dual licensed under the MIT and the University of Illinois Open
   6 // Source Licenses. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This file implements double-precision to integer conversion for the
  11 // compiler-rt library.  No range checking is performed; the behavior of this
  12 // conversion is undefined for out of range values in the C standard.
  13 //
  14 //===----------------------------------------------------------------------===//
  15
  16 #define DOUBLE_PRECISION
  17 #include "fp_lib.h"
  18
  19 #include "int_lib.h"
  20
  21 ARM_EABI_FNALIAS(d2iz, fixdfsi)
  22
  23 COMPILER_RT_ABI int
  24 __fixdfsi(fp_t a) {
  25
  26     // Break a into sign, exponent, significand
  27     const rep_t aRep = toRep(a);
  28     const rep_t aAbs = aRep & absMask;
  29     const int sign = aRep & signBit ? -1 : 1;
  30     const int exponent = (aAbs >> significandBits) - exponentBias;
  31     const rep_t significand = (aAbs & significandMask) | implicitBit;
  32
  33     // If 0 < exponent < significandBits, right shift to get the result.
  34     if ((unsigned int)exponent < significandBits) {
  35         return sign * (significand >> (significandBits - exponent));
  36     }
  37
  38     // If exponent is negative, the result is zero.
  39     else if (exponent < 0) {
  40         return 0;
  41     }
  42
  43     // If significandBits < exponent, left shift to get the result.  This shift
  44     // may end up being larger than the type width, which incurs undefined
  45     // behavior, but the conversion itself is undefined in that case, so
  46     // whatever the compiler decides to do is fine.
  47     else {
  48         return sign * (significand << (exponent - significandBits));
  49     }
  50 }