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 ; Log2.c 15 ; 16 ;Abstract: 17 ; 18 ; 64-bit integer logarithm function for IA-32 19 ; 20 ;--*/ 21 ; 22 ;--------------------------------------------------------------------------- 23 .686 24 .model flat,C 25 .code 26 27 ;--------------------------------------------------------------------------- 28 29 ;UINT8 30 ;Log2 ( 31 ; IN UINT64 Operand 32 ; ) 33 ;/*++ 34 ; 35 ;Routine Description: 36 ; 37 ; Calculates and floors logarithms based on 2 38 ; 39 ;Arguments: 40 ; 41 ; Operand - value to calculate logarithm 42 ; 43 ;Returns: 44 ; 45 ; The largest integer that is less than or equal 46 ; to the logarithm of Operand based on 2 47 ; 48 ;--*/ 49 Log2 PROC 50 mov ecx, 64 51 52 cmp dword ptr [esp + 4], 0 ; (UINT32 *(&Operand)) 53 jne _Log2_Wend 54 cmp dword ptr [esp + 8], 0 ; (UINT32 *(&Operand)) + 1 55 jne _Log2_Wend 56 mov cl, 0FFH 57 jmp _Log2_Done 58 59 _Log2_Wend: 60 dec ecx 61 cmp ecx, 32 62 jae _Log2_Higher 63 bt [esp + 4], ecx ; (UINT32 *(&Operand)) 64 jmp _Log2_Bit 65 66 _Log2_Higher: 67 mov eax, ecx 68 sub eax, 32 69 bt [esp + 8], eax ; (UINT32 *(&Operand)) + 1 70 71 _Log2_Bit: 72 jc _Log2_Done 73 jmp _Log2_Wend 74 75 _Log2_Done: 76 mov al, cl 77 78 ret 79 80 Log2 ENDP 81 END 82
