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special compact representation for userdata with no user values

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(a common case)
This commit is contained in:
Roberto Ierusalimschy
2018-02-26 10:35:03 -03:00
parent 38d3bc8909
commit 2952bc5fc9
2 changed files with 44 additions and 12 deletions
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37
lobject.h
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@@ -1,5 +1,5 @@
/*
** $Id: lobject.h,v 2.138 2018/02/25 12:48:16 roberto Exp roberto $
** $Id: lobject.h,v 2.139 2018/02/25 12:52:32 roberto Exp roberto $
** Type definitions for Lua objects
** See Copyright Notice in lua.h
*/
@@ -70,7 +70,7 @@ typedef struct TValue {
#define rttype(o) ((o)->tt_)
/* tag with no variants (bits 0-3) */
#define novariant(x) ((x) & 0x0F)
#define novariant(t) ((t) & 0x0F)
/* type tag of a TValue (bits 0-3 for tags + variant bits 4-5) */
#define ttyperaw(t) ((t) & 0x3F)
@@ -379,7 +379,7 @@ typedef union UTString {
*/
#define ttislightuserdata(o) checktag((o), LUA_TLIGHTUSERDATA)
#define ttisfulluserdata(o) checktag((o), ctb(LUA_TUSERDATA))
#define ttisfulluserdata(o) checktype((o), LUA_TUSERDATA)
#define pvalue(o) check_exp(ttislightuserdata(o), val_(o).p)
#define uvalue(o) check_exp(ttisfulluserdata(o), gco2u(val_(o).gc))
@@ -403,7 +403,8 @@ typedef union UValue {
/*
** Header for userdata; memory area follows the end of this structure.
** Header for userdata with user values;
** memory area follows the end of this structure.
*/
typedef struct Udata {
CommonHeader;
@@ -415,15 +416,33 @@ typedef struct Udata {
} Udata;
/* computes the offset of the memory area of a userdata */
#define udatamemoffset(nuv) (sizeof(Udata) + (sizeof(UValue) * ((nuv) - 1)))
/*
** Get the address of the memory block inside 'Udata'.
** Header for userdata with no user values. These userdata do not need
** to be gray during GC, and therefore do not need a 'gclist' field.
** To simplify, the code always use 'Udata' for both kinds of userdata,
** making sure it never accesses 'gclist' on userdata with no user values.
** This structure here is used only to compute the correct size for
** this representation. (The 'bindata' field in its end ensures correct
** alignment for binary data following this header.)
*/
typedef struct Udata0 {
CommonHeader;
unsigned short nuvalue; /* number of user values */
size_t len; /* number of bytes */
struct Table *metatable;
union {LUAI_MAXALIGN;} bindata;
} Udata0;
/* compute the offset of the memory area of a userdata */
#define udatamemoffset(nuv) \
((nuv) == 0 ? offsetof(Udata0, bindata) \
: offsetof(Udata, uv) + (sizeof(UValue) * (nuv)))
/* get the address of the memory block inside 'Udata' */
#define getudatamem(u) (cast_charp(u) + udatamemoffset((u)->nuvalue))
/* computes the size of a userdata */
/* compute the size of a userdata */
#define sizeudata(nuv,nb) (udatamemoffset(nuv) + (nb))
/* }================================================================== */