1214152Sed/* ===-- clzsi2.c - Implement __clzsi2 -------------------------------------=== 2214152Sed * 3222656Sed * The LLVM Compiler Infrastructure 4214152Sed * 5222656Sed * This file is dual licensed under the MIT and the University of Illinois Open 6222656Sed * Source Licenses. See LICENSE.TXT for details. 7214152Sed * 8214152Sed * ===----------------------------------------------------------------------=== 9214152Sed * 10214152Sed * This file implements __clzsi2 for the compiler_rt library. 11214152Sed * 12214152Sed * ===----------------------------------------------------------------------=== 13214152Sed */ 14214152Sed 15214152Sed#include "int_lib.h" 16214152Sed 17214152Sed/* Returns: the number of leading 0-bits */ 18214152Sed 19214152Sed/* Precondition: a != 0 */ 20214152Sed 21222656SedCOMPILER_RT_ABI si_int 22214152Sed__clzsi2(si_int a) 23214152Sed{ 24214152Sed su_int x = (su_int)a; 25214152Sed si_int t = ((x & 0xFFFF0000) == 0) << 4; /* if (x is small) t = 16 else 0 */ 26214152Sed x >>= 16 - t; /* x = [0 - 0xFFFF] */ 27214152Sed su_int r = t; /* r = [0, 16] */ 28214152Sed /* return r + clz(x) */ 29214152Sed t = ((x & 0xFF00) == 0) << 3; 30214152Sed x >>= 8 - t; /* x = [0 - 0xFF] */ 31214152Sed r += t; /* r = [0, 8, 16, 24] */ 32214152Sed /* return r + clz(x) */ 33214152Sed t = ((x & 0xF0) == 0) << 2; 34214152Sed x >>= 4 - t; /* x = [0 - 0xF] */ 35214152Sed r += t; /* r = [0, 4, 8, 12, 16, 20, 24, 28] */ 36214152Sed /* return r + clz(x) */ 37214152Sed t = ((x & 0xC) == 0) << 1; 38214152Sed x >>= 2 - t; /* x = [0 - 3] */ 39214152Sed r += t; /* r = [0 - 30] and is even */ 40214152Sed /* return r + clz(x) */ 41214152Sed/* switch (x) 42214152Sed * { 43214152Sed * case 0: 44214152Sed * return r + 2; 45214152Sed * case 1: 46214152Sed * return r + 1; 47214152Sed * case 2: 48214152Sed * case 3: 49214152Sed * return r; 50214152Sed * } 51214152Sed */ 52214152Sed return r + ((2 - x) & -((x & 2) == 0)); 53214152Sed} 54