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Minor refactoring of the expression-compaction logic for clarity of

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presentation.  New comments added.  The EXPRDUP_DISTINCTSPAN flag is
removed as obsolete. (CVS 6470)

FossilOrigin-Name: 44ded2ea67374f187a111df69c3f51f866735400
This commit is contained in:
drh
2009-04-08 13:51:51 +00:00
parent 0a9aa2253c
commit 12ffee8cb9
7 changed files with 88 additions and 88 deletions
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42
src/sqliteInt.h
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@@ -11,7 +11,7 @@
*************************************************************************
** Internal interface definitions for SQLite.
**
** @(#) $Id: sqliteInt.h,v 1.853 2009/04/07 22:06:57 drh Exp $
** @(#) $Id: sqliteInt.h,v 1.854 2009/04/08 13:51:51 drh Exp $
*/
#ifndef _SQLITEINT_H_
#define _SQLITEINT_H_
@@ -1452,19 +1452,18 @@ struct AggInfo {
**
** ALLOCATION NOTES:
**
** Expr structures may be stored as part of the in-memory database schema,
** for example as part of trigger, view or table definitions. In this case,
** the amount of memory consumed by complex expressions may be significant.
** For this reason, less than sizeof(Expr) bytes may be allocated for some
** Expr structs stored as part of the in-memory database schema.
** Expr objects can use a lot of memory space in database schema. To
** help reduce memory requirements, sometimes an Expr object will be
** truncated. And to reduce the number of memory allocations, sometimes
** two or more Expr objects will be stored in a single memory allocation,
** together with Expr.token and/or Expr.span strings.
**
** If the EP_Reduced flag is set in Expr.flags, then only EXPR_REDUCEDSIZE
** bytes of space are allocated for the expression structure. This is enough
** space to store all fields up to and including the "Token span;" field.
**
** If the EP_TokenOnly flag is set in Expr.flags, then only EXPR_TOKENONLYSIZE
** bytes of space are allocated for the expression structure. This is enough
** space to store all fields up to and including the "Token token;" field.
** If the EP_Reduced, EP_SpanToken, and EP_TokenOnly flags are set when
** an Expr object is truncated. When EP_Reduced is set, then all
** the child Expr objects in the Expr.pLeft and Expr.pRight subtrees
** are contained within the same memory allocation. Note, however, that
** the subtrees in Expr.x.pList or Expr.x.pSelect are always separately
** allocated, regardless of whether or not EP_Reduced is set.
*/
struct Expr {
u8 op; /* Operation performed by this node */
@@ -1480,7 +1479,7 @@ struct Expr {
Token span; /* Complete text of the expression */
/* If the EP_SpanOnly flag is set in the Expr.flags mask, then no
/* If the EP_SpanToken flag is set in the Expr.flags mask, then no
** space is allocated for the fields below this point. An attempt to
** access them will result in a segfault or malfunction.
*********************************************************************/
@@ -1528,7 +1527,7 @@ struct Expr {
#define EP_Reduced 0x2000 /* Expr struct is EXPR_REDUCEDSIZE bytes only */
#define EP_TokenOnly 0x4000 /* Expr struct is EXPR_TOKENONLYSIZE bytes only */
#define EP_SpanOnly 0x8000 /* Expr struct is EXPR_SPANONLYSIZE bytes only */
#define EP_SpanToken 0x8000 /* Expr size is EXPR_SPANTOKENSIZE bytes */
/*
** The following are the meanings of bits in the Expr.vvaFlags field.
@@ -1553,18 +1552,17 @@ struct Expr {
** struct, an Expr struct with the EP_Reduced flag set in Expr.flags
** and an Expr struct with the EP_TokenOnly flag set.
*/
#define EXPR_FULLSIZE sizeof(Expr)
#define EXPR_REDUCEDSIZE offsetof(Expr,iTable)
#define EXPR_TOKENONLYSIZE offsetof(Expr,span)
#define EXPR_SPANONLYSIZE offsetof(Expr,pLeft)
#define EXPR_FULLSIZE sizeof(Expr) /* Full size */
#define EXPR_REDUCEDSIZE offsetof(Expr,iTable) /* Common features */
#define EXPR_SPANTOKENSIZE offsetof(Expr,pLeft) /* Fewer features */
#define EXPR_TOKENONLYSIZE offsetof(Expr,span) /* Smallest possible */
/*
** Flags passed to the sqlite3ExprDup() function. See the header comment
** above sqlite3ExprDup() for details.
*/
#define EXPRDUP_REDUCE 0x0001
#define EXPRDUP_SPAN 0x0002
#define EXPRDUP_DISTINCTSPAN 0x0004
#define EXPRDUP_REDUCE 0x0001 /* Used reduced-size Expr nodes */
#define EXPRDUP_SPAN 0x0002 /* Make a copy of Expr.span */
/*
** A list of expressions. Each expression may optionally have a