compiler-rt/lib/builtins/ctzdi2.c

   1 //===-- ctzdi2.c - Implement __ctzdi2 -------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file implements __ctzdi2 for the compiler_rt library.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "int_lib.h"
  14
  15 // Returns: the number of trailing 0-bits
  16
  17 #if !defined(__clang__) &&                                                     \
  18     ((defined(__sparc__) && defined(__arch64__)) || defined(__mips64) ||       \
  19      (defined(__riscv) && __SIZEOF_POINTER__ >= 8))
  20 // On 64-bit architectures with neither a native clz instruction nor a native
  21 // ctz instruction, gcc resolves __builtin_ctz to __ctzdi2 rather than
  22 // __ctzsi2, leading to infinite recursion.
  23 #define __builtin_ctz(a) __ctzsi2(a)
  24 extern int __ctzsi2(si_int);
  25 #endif
  26
  27 // Precondition: a != 0
  28
  29 COMPILER_RT_ABI int __ctzdi2(di_int a) {
  30   dwords x;
  31   x.all = a;
  32   const si_int f = -(x.s.low == 0);
  33   return ctzsi((x.s.high & f) | (x.s.low & ~f)) +
  34          (f & ((si_int)(sizeof(si_int) * CHAR_BIT)));
  35 }