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Clean up FAT12 handling -- there's a portable approach that's small too. 

git-svn-id: https://svn.code.sf.net/p/freedos/svn/kernel/trunk@908 6ac86273-5f31-0410-b378-82cca8765d1b
This commit is contained in:
Bart Oldeman 2004-04-30 15:28:18 +00:00
parent 126ef5cec9
commit 00e1527fc5
1 changed files with 18 additions and 28 deletions
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46
kernel/fattab.c
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@ -184,10 +184,7 @@ CLUSTER link_fat(struct dpb FAR * dpbp, CLUSTER Cluster1,
{
REG UBYTE FAR *fbp0, FAR * fbp1;
struct buffer FAR * bp1;
union {
UBYTE bytes[2];
unsigned word;
} clusterbuff;
unsigned cluster;
/* form an index so that we can read the block as a */
/* byte array */
@ -197,15 +194,14 @@ CLUSTER link_fat(struct dpb FAR * dpbp, CLUSTER Cluster1,
/* it does, get the next block and use both to form the */
/* the FAT word. Otherwise, just point to the next */
/* block. */
clusterbuff.bytes[0] = bp->b_buffer[idx];
/* next byte, will be overwritten, if not valid */
clusterbuff.bytes[1] = bp->b_buffer[idx + 1];
fbp0 = &bp->b_buffer[idx];
/* pointer to next byte, will be overwritten, if not valid */
fbp1 = fbp0 + 1;
if (idx >= (unsigned)dpbp->dpb_secsize - 1)
{
/* blockio.c LRU logic ensures that bp != bp1 */
bp1 = getFATblock(dpbp, (unsigned)clussec + 1);
if (bp1 == 0)
return 1; /* the only error code possible here */
@ -214,27 +210,17 @@ CLUSTER link_fat(struct dpb FAR * dpbp, CLUSTER Cluster1,
bp1->b_flag |= BFR_DIRTY | BFR_VALID;
fbp1 = &bp1->b_buffer[0];
clusterbuff.bytes[1] = bp1->b_buffer[0];
}
idx = *fbp0 | (*fbp1 << 8);
if (Cluster2 == READ_CLUSTER)
{
/* Now to unpack the contents of the FAT entry. Odd and */
/* even bytes are packed differently. */
#ifndef I86 /* the latter assumes byte ordering */
if (Cluster1 & 0x01)
idx =
((clusterbuff.bytes[0] & 0xf0) >> 4) | (clusterbuff.bytes[1] << 4);
else
idx = clusterbuff.bytes[0] | ((clusterbuff.bytes[1] & 0x0f) << 8);
#else
if (Cluster1 & 0x01)
idx = (unsigned short)clusterbuff.word >> 4;
else
idx = clusterbuff.word & 0x0fff;
#endif
idx >>= 4;
idx &= 0x0fff;
if (idx >= MASK12)
return LONG_LAST_CLUSTER;
@ -243,19 +229,23 @@ CLUSTER link_fat(struct dpb FAR * dpbp, CLUSTER Cluster1,
return idx;
}
/* Cluster2 may be set to LONG_LAST_CLUSTER == 0x0FFFFFFFUL or 0xFFFF */
/* -- please don't remove this mask! */
cluster = (unsigned)Cluster2 & 0x0fff;
/* Now pack the value in */
if ((unsigned)Cluster1 & 0x01)
{
*fbp0 = (*fbp0 & 0x0f) | (UBYTE)((UBYTE)Cluster2 << 4);
*fbp1 = (UBYTE)((unsigned)Cluster2 >> 4);
idx &= 0x000f;
cluster <<= 4;
}
else
{
*fbp0 = (UBYTE)Cluster2;
/* Cluster2 may be set to LONG_LAST_CLUSTER == 0x0FFFFFFFUL or 0xFFFF */
/* -- please don't optimize to (UBYTE)((unsigned)Cluster2 >> 8)! */
*fbp1 = (*fbp1 & 0xf0) | ((UBYTE)((unsigned)Cluster2 >> 8) & 0x0f);
idx &= 0xf000;
}
cluster |= idx;
*fbp0 = (UBYTE)cluster;
*fbp1 = (UBYTE)(cluster >> 8);
}
else if (ISFAT16(dpbp))
{