1 /*++ 2 3 Copyright (c) 2006, Intel Corporation. All rights reserved.<BR> 4 This program and the accompanying materials 5 are licensed and made available under the terms and conditions of the BSD License 6 which accompanies this distribution. The full text of the license may be found at 7 http://opensource.org/licenses/bsd-license.php 8 9 THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, 10 WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED. 11 12 Module Name: 13 14 GetPowerOfTwo.c 15 16 Abstract: 17 18 Calculates the largest integer that is both 19 a power of two and less than Input 20 21 --*/ 22 23 #include "Tiano.h" 24 25 UINT64 26 GetPowerOfTwo ( 27 IN UINT64 Input 28 ) 29 /*++ 30 31 Routine Description: 32 33 Calculates the largest integer that is both 34 a power of two and less than Input 35 36 Arguments: 37 38 Input - value to calculate power of two 39 40 Returns: 41 42 the largest integer that is both a power of 43 two and less than Input 44 45 --*/ 46 { 47 __asm { 48 xor eax, eax 49 mov edx, eax 50 mov ecx, dword ptr Input[4] 51 jecxz _F 52 bsr ecx, ecx 53 bts edx, ecx 54 jmp _Exit 55 _F: 56 mov ecx, dword ptr Input[0] 57 jecxz _Exit 58 bsr ecx, ecx 59 bts eax, ecx 60 _Exit: 61 } 62 } 63
