78 lines
1.4 KiB
C
78 lines
1.4 KiB
C
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/*++
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Copyright (c) 1997 Microsoft Corporation
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Module Name:
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trackbuf.c
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Abstract:
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Routine to allocate a buffer suitable for i/o a track
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at a time.
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Author:
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Ted Miller (tedm) 29-May-1997
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Revision History:
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--*/
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#include <mytypes.h>
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#include <misclib.h>
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#include <malloc.h>
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BOOL
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_far
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AllocTrackBuffer(
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IN BYTE SectorsPerTrack,
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OUT FPVOID _far *AlignedBuffer,
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OUT FPVOID _far *Buffer
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)
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{
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FPVOID p;
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ULONG u;
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//
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//
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// We allocate twice the size we need because we will need to ensure
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// that the buffer doesn't cross a 64K physical boundary.
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// NOTE: sectors per track is assumed to be max 63!
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//
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if(SectorsPerTrack > 63) {
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return(FALSE);
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}
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p = malloc(SectorsPerTrack * 512 * 2);
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if(!p) {
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return(FALSE);
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}
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//
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// Calculate physical address of buffer.
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//
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u = ((ULONG)p & 0xffffL) + (((ULONG)p >> 16) << 4);
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//
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// Figure out whether the buffer crosses a 64k boundary.
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// If it does, we allocated enough to relocate it
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// to the next 64k boundary.
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//
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if((u & 0xf0000L) != ((u + (512*SectorsPerTrack)) & 0xf0000L)) {
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u = (u & 0xf0000L) + 0x10000;
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}
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//
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// Convert back to seg:offset. The conversion guarantees that
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// the offset will be in the range 0-f.
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//
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*AlignedBuffer = (FPVOID)(((u >> 4) << 16) + (u & 0xf));
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*Buffer = p;
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return(TRUE);
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}
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