1 //===-- clzdi2.c - Implement __clzdi2 -------------------------------------===//
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 __clzdi2 for the compiler_rt library.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "int_lib.h"
14 
15 // Returns: the number of leading 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_clz to __clzdi2 rather than
22 // __clzsi2, leading to infinite recursion.
23 #define __builtin_clz(a) __clzsi2(a)
24 extern int __clzsi2(si_int);
25 #endif
26 
27 // Precondition: a != 0
28 
__clzdi2(di_int a)29 COMPILER_RT_ABI int __clzdi2(di_int a) {
30   dwords x;
31   x.all = a;
32   const si_int f = -(x.s.high == 0);
33   return clzsi((x.s.high & ~f) | (x.s.low & f)) +
34          (f & ((si_int)(sizeof(si_int) * CHAR_BIT)));
35 }
36