src/compiler-rt/lib/builtins/ffsdi2.c

   1 /* ===-- ffsdi2.c - Implement __ffsdi2 -------------------------------------===
   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 __ffsdi2 for the compiler_rt library.
  11  *
  12  * ===----------------------------------------------------------------------===
  13  */
  14
  15 #include "int_lib.h"
  16
  17 /* Returns: the index of the least significant 1-bit in a, or
  18  * the value zero if a is zero. The least significant bit is index one.
  19  */
  20
  21 COMPILER_RT_ABI si_int
  22 __ffsdi2(di_int a)
  23 {
  24     dwords x;
  25     x.all = a;
  26     if (x.s.low == 0)
  27     {
  28         if (x.s.high == 0)
  29             return 0;
  30         return __builtin_ctz(x.s.high) + (1 + sizeof(si_int) * CHAR_BIT);
  31     }
  32     return __builtin_ctz(x.s.low) + 1;
  33 }