36 lines · c
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-exception6//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-bits16 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 native20// ctz instruction, `__builtin_clz` resolves to `__clzdi2` rather than21// __clzsi2 as libgcc does not ship with `__clzsi2`, leading to infinite22// recursion.23#define __builtin_clz(a) __clzsi2(a)24extern int __clzsi2(si_int);25#endif26 27// Precondition: a != 028 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