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SQLite ODBC Driver SQLite3 的ODBC驱动

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<H2> 8.4 Types </H2>
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<P>

The types are stored in a single 'int' variable. It was choosen in the
first stages of development when tcc was much simpler. Now, it may not
be the best solution.
</P><P>

<TABLE><tr><td>&nbsp;</td><td class=example><pre>#define VT_INT        0  /* integer type */
#define VT_BYTE       1  /* signed byte type */
#define VT_SHORT      2  /* short type */
#define VT_VOID       3  /* void type */
#define VT_PTR        4  /* pointer */
#define VT_ENUM       5  /* enum definition */
#define VT_FUNC       6  /* function type */
#define VT_STRUCT     7  /* struct/union definition */
#define VT_FLOAT      8  /* IEEE float */
#define VT_DOUBLE     9  /* IEEE double */
#define VT_LDOUBLE   10  /* IEEE long double */
#define VT_BOOL      11  /* ISOC99 boolean type */
#define VT_LLONG     12  /* 64 bit integer */
#define VT_LONG      13  /* long integer (NEVER USED as type, only
                            during parsing) */
#define VT_BTYPE      0x000f /* mask for basic type */
#define VT_UNSIGNED   0x0010  /* unsigned type */
#define VT_ARRAY      0x0020  /* array type (also has VT_PTR) */
#define VT_BITFIELD   0x0040  /* bitfield modifier */

#define VT_STRUCT_SHIFT 16   /* structure/enum name shift (16 bits left) */
</pre></td></tr></table></P><P>

When a reference to another type is needed (for pointers, functions and
structures), the <CODE>32 - VT_STRUCT_SHIFT</CODE> high order bits are used to
store an identifier reference.
</P><P>

The <CODE>VT_UNSIGNED</CODE> flag can be set for chars, shorts, ints and long
longs.
</P><P>

Arrays are considered as pointers <CODE>VT_PTR</CODE> with the flag
<CODE>VT_ARRAY</CODE> set.
</P><P>

The <CODE>VT_BITFIELD</CODE> flag can be set for chars, shorts, ints and long
longs. If it is set, then the bitfield position is stored from bits
VT_STRUCT_SHIFT to VT_STRUCT_SHIFT + 5 and the bit field size is stored
from bits VT_STRUCT_SHIFT + 6 to VT_STRUCT_SHIFT + 11.
</P><P>

<CODE>VT_LONG</CODE> is never used except during parsing.
</P><P>

During parsing, the storage of an object is also stored in the type
integer:
</P><P>

<TABLE><tr><td>&nbsp;</td><td class=example><pre>#define VT_EXTERN  0x00000080  /* extern definition */
#define VT_STATIC  0x00000100  /* static variable */
#define VT_TYPEDEF 0x00000200  /* typedef definition */
</pre></td></tr></table></P><P>

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<H2> 8.5 Symbols </H2>
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<P>

All symbols are stored in hashed symbol stacks. Each symbol stack
contains <CODE>Sym</CODE> structures.
</P><P>

<CODE>Sym.v</CODE> contains the symbol name (remember
an idenfier is also a token, so a string is never necessary to store
it). <CODE>Sym.t</CODE> gives the type of the symbol. <CODE>Sym.r</CODE> is usually
the register in which the corresponding variable is stored. <CODE>Sym.c</CODE> is
usually a constant associated to the symbol.
</P><P>

Four main symbol stacks are defined:
</P><P>

<DL COMPACT>

<DT><CODE>define_stack</CODE>
<DD>for the macros (<CODE>#define</CODE>s).
<P>

<DT><CODE>global_stack</CODE>
<DD>for the global variables, functions and types.
<P>

<DT><CODE>local_stack</CODE>
<DD>for the local variables, functions and types.
<P>

<DT><CODE>global_label_stack</CODE>
<DD>for the local labels (for <CODE>goto</CODE>).
<P>

<DT><CODE>label_stack</CODE>
<DD>for GCC block local labels (see the <CODE>__label__</CODE> keyword).
<P>

</DL>
<P>

<CODE>sym_push()</CODE> is used to add a new symbol in the local symbol
stack. If no local symbol stack is active, it is added in the global
symbol stack.
</P><P>

<CODE>sym_pop(st,b)</CODE> pops symbols from the symbol stack <VAR>st</VAR> until
the symbol <VAR>b</VAR> is on the top of stack. If <VAR>b</VAR> is NULL, the stack
is emptied.
</P><P>

<CODE>sym_find(v)</CODE> return the symbol associated to the identifier
<VAR>v</VAR>. The local stack is searched first from top to bottom, then the
global stack.
</P><P>

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<H2> 8.6 Sections </H2>
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<P>

The generated code and datas are written in sections. The structure
<CODE>Section</CODE> contains all the necessary information for a given
section. <CODE>new_section()</CODE> creates a new section. ELF file semantics
is assumed for each section.
</P><P>

The following sections are predefined:
</P><P>

<DL COMPACT>

<DT><CODE>text_section</CODE>
<DD>is the section containing the generated code. <VAR>ind</VAR> contains the
current position in the code section.
<P>

<DT><CODE>data_section</CODE>
<DD>contains initialized data
<P>

<DT><CODE>bss_section</CODE>
<DD>contains uninitialized data
<P>

<DT><CODE>bounds_section</CODE>
<DD><DT><CODE>lbounds_section</CODE>
<DD>are used when bound checking is activated
<P>

<DT><CODE>stab_section</CODE>
<DD><DT><CODE>stabstr_section</CODE>
<DD>are used when debugging is actived to store debug information
<P>

<DT><CODE>symtab_section</CODE>
<DD><DT><CODE>strtab_section</CODE>
<DD>contain the exported symbols (currently only used for debugging).
<P>

</DL>
<P>

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<H2> 8.7 Code generation </H2>
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<P>

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<H3> 8.7.1 Introduction </H3>
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<P>

The TCC code generator directly generates linked binary code in one
pass. It is rather unusual these days (see gcc for example which
generates text assembly), but it can be very fast and surprisingly
little complicated.
</P><P>

The TCC code generator is register based. Optimization is only done at
the expression level. No intermediate representation of expression is
kept except the current values stored in the <EM>value stack</EM>.
</P><P>

On x86, three temporary registers are used. When more registers are
needed, one register is spilled into a new temporary variable on the stack.
</P><P>

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<H3> 8.7.2 The value stack </H3>
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<P>

When an expression is parsed, its value is pushed on the value stack
(<VAR>vstack</VAR>). The top of the value stack is <VAR>vtop</VAR>. Each value
stack entry is the structure <CODE>SValue</CODE>.
</P><P>

<CODE>SValue.t</CODE> is the type. <CODE>SValue.r</CODE> indicates how the value is
currently stored in the generated code. It is usually a CPU register
index (<CODE>REG_xxx</CODE> constants), but additional values and flags are
defined:
</P><P>

<TABLE><tr><td>&nbsp;</td><td class=example><pre>#define VT_CONST     0x00f0
#define VT_LLOCAL    0x00f1
#define VT_LOCAL     0x00f2
#define VT_CMP       0x00f3
#define VT_JMP       0x00f4
#define VT_JMPI      0x00f5
#define VT_LVAL      0x0100
#define VT_SYM       0x0200
#define VT_MUSTCAST  0x0400
#define VT_MUSTBOUND 0x0800
#define VT_BOUNDED   0x8000
#define VT_LVAL_BYTE     0x1000
#define VT_LVAL_SHORT    0x2000
#define VT_LVAL_UNSIGNED 0x4000
#define VT_LVAL_TYPE     (VT_LVAL_BYTE | VT_LVAL_SHORT | VT_LVAL_UNSIGNED)
</pre></td></tr></table></P><P>

<DL COMPACT>

<DT><CODE>VT_CONST</CODE>
<DD>indicates that the value is a constant. It is stored in the union
<CODE>SValue.c</CODE>, depending on its type.
<P>

<DT><CODE>VT_LOCAL</CODE>
<DD>indicates a local variable pointer at offset <CODE>SValue.c.i</CODE> in the
stack.
<P>

<DT><CODE>VT_CMP</CODE>
<DD>indicates that the value is actually stored in the CPU flags (i.e. the
value is the consequence of a test). The value is either 0 or 1. The
actual CPU flags used is indicated in <CODE>SValue.c.i</CODE>. 
<P>

If any code is generated which destroys the CPU flags, this value MUST be
put in a normal register.
</P><P>

<DT><CODE>VT_JMP</CODE>
<DD><DT><CODE>VT_JMPI</CODE>
<DD>indicates that the value is the consequence of a conditional jump. For VT_JMP,
it is 1 if the jump is taken, 0 otherwise. For VT_JMPI it is inverted.
<P>

These values are used to compile the <CODE>||</CODE> and <CODE>&#38;&#38;