92 lines
1.7 KiB
C
92 lines
1.7 KiB
C
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/*++
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Copyright (c) 2000 Microsoft Corporation
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Module Name:
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timindex.asm
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Abstract:
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This module implements the code necessary to compute the timer table
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index for a timer.
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Author:
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David N. Cutler (davec) 16-Jun-2000
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Environment:
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Any mode.
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Revision History:
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--*/
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#include "ki.h"
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ULONG
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KiComputeTimerTableIndex (
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IN LARGE_INTEGER Interval,
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IN LARGE_INTEGER CurrentTime,
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IN PKTIMER Timer
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)
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/*++
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Routine Description:
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This function computes the timer table index for the specified timer
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object and stores the due time in the timer object.
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N.B. The interval parameter is guaranteed to be negative since it is
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expressed as relative time.
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The formula for due time calculation is:
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Due Time = Current Time - Interval
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The formula for the index calculation is:
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Index = (Due Time / Maximum time) & (Table Size - 1)
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The time increment division is performed using reciprocal multiplication.
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Arguments:
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Interval - Supplies the relative time at which the timer is to
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expire.
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CurrentCount - Supplies the current system tick count.
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Timer - Supplies a pointer to a dispatch object of type timer.
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Return Value:
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The time table index is returned as the function value and the due
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time is stored in the timer object.
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--*/
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{
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LONG64 DueTime;
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LONG64 HighTime;
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ULONG Index;
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//
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// Compute the due time of the timer.
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//
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DueTime = CurrentTime.QuadPart - Interval.QuadPart;
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Timer->DueTime.QuadPart = DueTime;
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//
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// Compute the timer table index.
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//
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HighTime = MultiplyHigh(DueTime, KiTimeIncrementReciprocal.QuadPart);
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Index = (ULONG)(HighTime >> KiTimeIncrementShiftCount);
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return (Index & (TIMER_TABLE_SIZE - 1));
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}
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