*init

1 files changed, 194 insertions, 0 deletions

diff --git a/lstring.c b/lstring.c
new file mode 100644
index 0000000..3879a75
--- /dev/null
+++ b/lstring.c
@@ -0,0 +1,194 @@
+/*
+** $Id: lstring.c,v 2.26.1.1 2013/04/12 18:48:47 roberto Exp $
+** String table (keeps all strings handled by Lua)
+** See Copyright Notice in lua.h
+*/
+
+
+#include <string.h>
+
+#define lstring_c
+#define LUA_CORE
+
+#include "lua.h"
+
+#include "lmem.h"
+#include "lobject.h"
+#include "lstate.h"
+#include "lstring.h"
+
+
+/*
+** Lua will use at most ~(2^LUAI_HASHLIMIT) bytes from a string to
+** compute its hash
+*/
+#if !defined(LUAI_HASHLIMIT)
+#define LUAI_HASHLIMIT		5
+#endif
+
+
+// saw 长字符串相等
+/*
+** equality for long strings
+*/
+int luaS_eqlngstr (TString *a, TString *b) {
+  size_t len = a->tsv.len;
+  lua_assert(a->tsv.tt == LUA_TLNGSTR && b->tsv.tt == LUA_TLNGSTR);
+  return (a == b) ||  /* same instance or... */
+    ((len == b->tsv.len) &&  /* equal length and ... */
+     (memcmp(getstr(a), getstr(b), len) == 0));  /* equal contents */
+}
+
+
+// saw 判断字符串相等
+// 短字符串直接判断地址
+// 长字符串判断用顺序：地址 -> 长度 && 内容
+/*
+** equality for strings
+*/
+int luaS_eqstr (TString *a, TString *b) {
+  return (a->tsv.tt == b->tsv.tt) &&
+         (a->tsv.tt == LUA_TSHRSTR ? eqshrstr(a, b) : luaS_eqlngstr(a, b));
+}
+
+
+// saw 计算长字符串的hash
+unsigned int luaS_hash (const char *str, size_t l, unsigned int seed) {
+  unsigned int h = seed ^ cast(unsigned int, l);
+  size_t l1;
+  size_t step = (l >> LUAI_HASHLIMIT) + 1;
+  for (l1 = l; l1 >= step; l1 -= step)
+    h = h ^ ((h<<5) + (h>>2) + cast_byte(str[l1 - 1]));
+  return h;
+}
+
+
+// saw 将 g->strt 扩容，预防哈希冲突
+/*
+** resizes the string table
+*/
+void luaS_resize (lua_State *L, int newsize) {
+  int i;
+  stringtable *tb = &G(L)->strt;
+  /* cannot resize while GC is traversing strings */
+  luaC_runtilstate(L, ~bitmask(GCSsweepstring));
+  if (newsize > tb->size) {
+    luaM_reallocvector(L, tb->hash, tb->size, newsize, GCObject *);
+    for (i = tb->size; i < newsize; i++) tb->hash[i] = NULL;
+  }
+  /* rehash */
+  for (i=0; i<tb->size; i++) {
+    GCObject *p = tb->hash[i];
+    tb->hash[i] = NULL;
+    while (p) {  /* for each node in the list */
+      GCObject *next = gch(p)->next;  /* save next */
+      unsigned int h = lmod(gco2ts(p)->hash, newsize);  /* new position */
+      gch(p)->next = tb->hash[h];  /* chain it */
+      tb->hash[h] = p;
+      resetoldbit(p);  /* see MOVE OLD rule */
+      p = next;
+    }
+  }
+  if (newsize < tb->size) {
+    /* shrinking slice must be empty */
+    lua_assert(tb->hash[newsize] == NULL && tb->hash[tb->size - 1] == NULL);
+    luaM_reallocvector(L, tb->hash, tb->size, newsize, GCObject *);
+  }
+  tb->size = newsize;
+}
+
+
+// saw 构造 lua string 对象
+/*
+** creates a new string object
+*/
+static TString *createstrobj (lua_State *L, const char *str, size_t l,
+                              int tag, unsigned int h, GCObject **list) {
+  TString *ts;
+  size_t totalsize;  /* total size of TString object */
+  totalsize = sizeof(TString) + ((l + 1) * sizeof(char));
+  ts = &luaC_newobj(L, tag, totalsize, list, 0)->ts;
+  ts->tsv.len = l;
+  ts->tsv.hash = h;
+  ts->tsv.extra = 0;
+  memcpy(ts+1, str, l*sizeof(char));
+	// C 风格的结尾，用来和C做交互时用，不需要显式的转换。和lua内部的内存块+长度风格不冲突
+  ((char *)(ts+1))[l] = '\0';  /* ending 0 */
+  return ts;
+}
+
+
+/*
+** creates a new short string, inserting it into string table
+*/
+static TString *newshrstr (lua_State *L, const char *str, size_t l,
+                                       unsigned int h) {
+  GCObject **list;  /* (pointer to) list where it will be inserted */
+  stringtable *tb = &G(L)->strt;
+  TString *s;
+  if (tb->nuse >= cast(lu_int32, tb->size) && tb->size <= MAX_INT/2)
+    luaS_resize(L, tb->size*2);  /* too crowded */
+  list = &tb->hash[lmod(h, tb->size)];
+  s = createstrobj(L, str, l, LUA_TSHRSTR, h, list);
+  tb->nuse++;
+  return s;
+}
+
+// saw 短字符串的内部化，保存在global_state中的strt里
+/*
+** checks whether short string exists and reuses it or creates a new one
+*/
+static TString *internshrstr (lua_State *L, const char *str, size_t l) {
+  GCObject *o;
+  global_State *g = G(L);
+  unsigned int h = luaS_hash(str, l, g->seed);
+  for (o = g->strt.hash[lmod(h, g->strt.size)]; // 遍历相同hash值的字符串链表
+       o != NULL;
+       o = gch(o)->next) {
+    TString *ts = rawgco2ts(o);
+    if (h == ts->tsv.hash &&
+        l == ts->tsv.len &&
+        (memcmp(str, getstr(ts), l * sizeof(char)) == 0)) {
+      if (isdead(G(L), o))  /* string is dead (but was not collected yet)? */
+        changewhite(o);  /* resurrect it */
+      return ts;
+    }
+  }
+  return newshrstr(L, str, l, h);  /* not found; create a new string */
+}
+
+
+/*
+** new string (with explicit length)
+*/
+TString *luaS_newlstr (lua_State *L, const char *str, size_t l) {
+  if (l <= LUAI_MAXSHORTLEN)  /* short string? */
+    return internshrstr(L, str, l);
+  else {
+    if (l + 1 > (MAX_SIZET - sizeof(TString))/sizeof(char))
+      luaM_toobig(L);
+    return createstrobj(L, str, l, LUA_TLNGSTR, G(L)->seed, NULL);
+  }
+}
+
+
+/*
+** new zero-terminated string
+*/
+TString *luaS_new (lua_State *L, const char *str) {
+  return luaS_newlstr(L, str, strlen(str));
+}
+
+
+// saw 创建userdata
+Udata *luaS_newudata (lua_State *L, size_t s, Table *e) {
+  Udata *u;
+  if (s > MAX_SIZET - sizeof(Udata))
+    luaM_toobig(L);
+  u = &luaC_newobj(L, LUA_TUSERDATA, sizeof(Udata) + s, NULL, 0)->u;
+  u->uv.len = s;
+  u->uv.metatable = NULL;
+  u->uv.env = e;
+  return u;
+}
+