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Refactor local variable names in the freeSpace() routine of btree.c for

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improved understandability.

FossilOrigin-Name: 7e63089a191f29aefde05e89bb612f3036cfa034
This commit is contained in:
drh
2014-08-20 14:37:09 +00:00
parent a13d5072c4
commit 7fb91646b5
3 changed files with 52 additions and 48 deletions
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85
src/btree.c
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@@ -1290,28 +1290,30 @@ defragment_page:
/*
** Return a section of the pPage->aData to the freelist.
** The first byte of the new free block is pPage->aDisk[start]
** and the size of the block is "size" bytes.
** The first byte of the new free block is pPage->aData[iStart]
** and the size of the block is iSize bytes.
**
** Most of the effort here is involved in coalesing adjacent
** free blocks into a single big free block.
*/
static int freeSpace(MemPage *pPage, int start, int size){
int addr, pbegin, hdr;
int iLast; /* Largest possible freeblock offset */
unsigned char *data = pPage->aData;
static int freeSpace(MemPage *pPage, int iStart, int iSize){
int iPtr; /* Address of pointer to next freeblock */
int iFreeBlk; /* Address of the next freeblock */
int hdr; /* Page header size. 0 or 100 */
int iLast; /* Largest possible freeblock offset */
unsigned char *data = pPage->aData; /* Page content */
assert( pPage->pBt!=0 );
assert( sqlite3PagerIswriteable(pPage->pDbPage) );
assert( start>=pPage->hdrOffset+6+pPage->childPtrSize );
assert( (start + size) <= (int)pPage->pBt->usableSize );
assert( iStart>=pPage->hdrOffset+6+pPage->childPtrSize );
assert( (iStart + iSize) <= (int)pPage->pBt->usableSize );
assert( sqlite3_mutex_held(pPage->pBt->mutex) );
assert( size>=4 ); /* Minimum cell size is 4 */
assert( iSize>=4 ); /* Minimum cell size is 4 */
if( pPage->pBt->btsFlags & BTS_SECURE_DELETE ){
/* Overwrite deleted information with zeros when the secure_delete
** option is enabled */
memset(&data[start], 0, size);
memset(&data[iStart], 0, iSize);
}
/* Add the space back into the linked list of freeblocks. Note that
@@ -1324,53 +1326,56 @@ static int freeSpace(MemPage *pPage, int start, int size){
** the freelist.
*/
hdr = pPage->hdrOffset;
addr = hdr + 1;
iPtr = hdr + 1;
iLast = pPage->pBt->usableSize - 4;
assert( start<=iLast );
while( (pbegin = get2byte(&data[addr]))<start && pbegin>0 ){
if( pbegin<addr+4 ){
assert( iStart<=iLast );
while( (iFreeBlk = get2byte(&data[iPtr]))<iStart && iFreeBlk>0 ){
if( iFreeBlk<iPtr+4 ){
return SQLITE_CORRUPT_BKPT;
}
addr = pbegin;
iPtr = iFreeBlk;
}
if( pbegin>iLast ){
if( iFreeBlk>iLast ){
return SQLITE_CORRUPT_BKPT;
}
assert( pbegin>addr || pbegin==0 );
put2byte(&data[addr], start);
put2byte(&data[start], pbegin);
put2byte(&data[start+2], size);
pPage->nFree = pPage->nFree + (u16)size;
assert( iFreeBlk>iPtr || iFreeBlk==0 );
put2byte(&data[iPtr], iStart);
put2byte(&data[iStart], iFreeBlk);
put2byte(&data[iStart+2], iSize);
pPage->nFree = pPage->nFree + (u16)iSize;
/* Coalesce adjacent free blocks */
addr = hdr + 1;
while( (pbegin = get2byte(&data[addr]))>0 ){
int pnext, psize, x;
assert( pbegin>addr );
assert( pbegin <= (int)pPage->pBt->usableSize-4 );
pnext = get2byte(&data[pbegin]);
psize = get2byte(&data[pbegin+2]);
if( pbegin + psize + 3 >= pnext && pnext>0 ){
int frag = pnext - (pbegin+psize);
if( (frag<0) || (frag>(int)data[hdr+7]) ){
iPtr = hdr + 1;
while( (iFreeBlk = get2byte(&data[iPtr]))>0 ){
int iNextBlk; /* Next freeblock after iFreeBlk */
int szFreeBlk; /* Size of iFreeBlk */
assert( iFreeBlk>iPtr );
assert( iFreeBlk <= (int)pPage->pBt->usableSize-4 );
iNextBlk = get2byte(&data[iFreeBlk]);
szFreeBlk = get2byte(&data[iFreeBlk+2]);
if( iFreeBlk + szFreeBlk + 3 >= iNextBlk && iNextBlk>0 ){
int nFrag; /* Fragment bytes in between iFreeBlk and iNextBlk */
int x; /* Temp value */
nFrag = iNextBlk - (iFreeBlk+szFreeBlk);
if( (nFrag<0) || (nFrag>(int)data[hdr+7]) ){
return SQLITE_CORRUPT_BKPT;
}
data[hdr+7] -= (u8)frag;
x = get2byte(&data[pnext]);
put2byte(&data[pbegin], x);
x = pnext + get2byte(&data[pnext+2]) - pbegin;
put2byte(&data[pbegin+2], x);
data[hdr+7] -= (u8)nFrag;
x = get2byte(&data[iNextBlk]);
put2byte(&data[iFreeBlk], x);
x = iNextBlk + get2byte(&data[iNextBlk+2]) - iFreeBlk;
put2byte(&data[iFreeBlk+2], x);
}else{
addr = pbegin;
iPtr = iFreeBlk;
}
}
/* If the cell content area begins with a freeblock, remove it. */
if( data[hdr+1]==data[hdr+5] && data[hdr+2]==data[hdr+6] ){
int top;
pbegin = get2byte(&data[hdr+1]);
memcpy(&data[hdr+1], &data[pbegin], 2);
top = get2byte(&data[hdr+5]) + get2byte(&data[pbegin+2]);
iFreeBlk = get2byte(&data[hdr+1]);
memcpy(&data[hdr+1], &data[iFreeBlk], 2);
top = get2byte(&data[hdr+5]) + get2byte(&data[iFreeBlk+2]);
put2byte(&data[hdr+5], top);
}
assert( sqlite3PagerIswriteable(pPage->pDbPage) );