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1//===-- clzsi2.c - Implement __clzsi2 -------------------------------------===//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 __clzsi2 for the compiler_rt library.10//11//===----------------------------------------------------------------------===//12 13#include "int_lib.h"14 15// Returns: the number of leading 0-bits16 17// Precondition: a != 018 19COMPILER_RT_ABI int __clzsi2(si_int a) {20 su_int x = (su_int)a;21 si_int t = ((x & 0xFFFF0000) == 0) << 4; // if (x is small) t = 16 else 022 x >>= 16 - t; // x = [0 - 0xFFFF]23 su_int r = t; // r = [0, 16]24 // return r + clz(x)25 t = ((x & 0xFF00) == 0) << 3;26 x >>= 8 - t; // x = [0 - 0xFF]27 r += t; // r = [0, 8, 16, 24]28 // return r + clz(x)29 t = ((x & 0xF0) == 0) << 2;30 x >>= 4 - t; // x = [0 - 0xF]31 r += t; // r = [0, 4, 8, 12, 16, 20, 24, 28]32 // return r + clz(x)33 t = ((x & 0xC) == 0) << 1;34 x >>= 2 - t; // x = [0 - 3]35 r += t; // r = [0 - 30] and is even36 // return r + clz(x)37 // switch (x)38 // {39 // case 0:40 // return r + 2;41 // case 1:42 // return r + 1;43 // case 2:44 // case 3:45 // return r;46 // }47 return r + ((2 - x) & -((x & 2) == 0));48}49