| /*++ | |
| Copyright (c) 2006, Intel Corporation. All rights reserved.<BR> | |
| This program and the accompanying materials | |
| are licensed and made available under the terms and conditions of the BSD License | |
| which accompanies this distribution. The full text of the license may be found at | |
| http://opensource.org/licenses/bsd-license.php | |
| THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, | |
| WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED. | |
| Module Name: | |
| Log2.c | |
| Abstract: | |
| 64-bit integer logarithm function for IA-32 | |
| --*/ | |
| #include "Tiano.h" | |
| UINT8 | |
| Log2 ( | |
| IN UINT64 Operand | |
| ) | |
| /*++ | |
| Routine Description: | |
| Calculates and floors logarithms based on 2 | |
| Arguments: | |
| Operand - value to calculate logarithm | |
| Returns: | |
| The largest integer that is less than or equal | |
| to the logarithm of Operand based on 2 | |
| --*/ | |
| { | |
| __asm { | |
| mov ecx, 64 | |
| cmp dword ptr Operand[0], 0 | |
| jne _Log2_Wend | |
| cmp dword ptr Operand[4], 0 | |
| jne _Log2_Wend | |
| mov cl, 0FFH | |
| jmp _Log2_Done | |
| _Log2_Wend: | |
| dec ecx | |
| cmp ecx, 32 | |
| jae _Log2_Higher | |
| bt dword ptr Operand[0], ecx | |
| jmp _Log2_Bit | |
| _Log2_Higher: | |
| mov eax, ecx | |
| sub eax, 32 | |
| bt dword ptr Operand[4], eax | |
| _Log2_Bit: | |
| jc _Log2_Done | |
| jmp _Log2_Wend | |
| _Log2_Done: | |
| mov al, cl | |
| } | |
| } |