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TITLE Log2.asm: 64-bit integer logarithm function for IA-32
;------------------------------------------------------------------------------
;
; Copyright (c) 2004, Intel Corporation
; All rights reserved. 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.asm
;
; Abstract:
;
; 64-bit integer logarithm function for IA-32
;
;------------------------------------------------------------------------------
.686P
.XMM
.MODEL SMALL
.CODE
Log2 PROTO C Operand: QWORD
Log2 PROC C Operand: QWORD
;------------------------------------------------------------------------------
; 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
;------------------------------------------------------------------------------
push ecx
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
pop ecx
ret
Log2 ENDP
END
|
