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(__sparc__) && defined(__arch64__)) || defined(__mips64) || \
18 (defined(__riscv) && __SIZEOF_POINTER__ >= 8))
19// On 64-bit architectures with neither a native clz instruction nor a native
20// ctz instruction, `__builtin_clz` resolves to `__clzdi2` rather than
21// __clzsi2 as libgcc does not ship with `__clzsi2`, leading to infinite
22// recursion.
23#define __builtin_clz(a) __clzsi2(a)
24extern int __clzsi2(si_int);
25#endif
26
27// Precondition: a != 0
28
29COMPILER_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

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source code of compiler-rt/lib/builtins/clzdi2.c