mudgangster

lptree.cc (36573B)

---

 /*
 ** $Id: lptree.c,v 1.22 2016/09/13 18:10:22 roberto Exp $
 ** Copyright 2013, Lua.org & PUC-Rio  (see 'lpeg.html' for license)
 */
 
 #include <ctype.h>
 #include <limits.h>
 #include <string.h>
 
 
 #include "lua.h"
 #include "lauxlib.h"
 
 #include "lptypes.h"
 #include "lpcap.h"
 #include "lpcode.h"
 #include "lpprint.h"
 #include "lptree.h"
 
 
 /* number of siblings for each tree */
 const byte numsiblings[] = {
   0, 0, 0,	/* char, set, any */
   0, 0,		/* true, false */	
   1,		/* rep */
   2, 2,		/* seq, choice */
   1, 1,		/* not, and */
   0, 0, 2, 1,  /* call, opencall, rule, grammar */
   1,  /* behind */
   1, 1  /* capture, runtime capture */
 };
 
 
 static TTree *newgrammar (lua_State *L, int arg);
 
 
 /*
 ** returns a reasonable name for value at index 'idx' on the stack
 */
 static const char *val2str (lua_State *L, int idx) {
   const char *k = lua_tostring(L, idx);
   if (k != NULL)
     return lua_pushfstring(L, "%s", k);
   else
     return lua_pushfstring(L, "(a %s)", luaL_typename(L, idx));
 }
 
 
 /*
 ** Fix a TOpenCall into a TCall node, using table 'postable' to
 ** translate a key to its rule address in the tree. Raises an
 ** error if key does not exist.
 */
 static void fixonecall (lua_State *L, int postable, TTree *g, TTree *t) {
   int n;
   lua_rawgeti(L, -1, t->key);  /* get rule's name */
   lua_gettable(L, postable);  /* query name in position table */
   n = lua_tonumber(L, -1);  /* get (absolute) position */
   lua_pop(L, 1);  /* remove position */
   if (n == 0) {  /* no position? */
     lua_rawgeti(L, -1, t->key);  /* get rule's name again */
     luaL_error(L, "rule '%s' undefined in given grammar", val2str(L, -1));
   }
   t->tag = TCall;
   t->u.ps = n - (t - g);  /* position relative to node */
   assert(sib2(t)->tag == TRule);
   sib2(t)->key = t->key;  /* fix rule's key */
 }
 
 
 /*
 ** Transform left associative constructions into right
 ** associative ones, for sequence and choice; that is:
 ** (t11 + t12) + t2  =>  t11 + (t12 + t2)
 ** (t11 * t12) * t2  =>  t11 * (t12 * t2)
 ** (that is, Op (Op t11 t12) t2 => Op t11 (Op t12 t2))
 */
 static void correctassociativity (TTree *tree) {
   TTree *t1 = sib1(tree);
   assert(tree->tag == TChoice || tree->tag == TSeq);
   while (t1->tag == tree->tag) {
     int n1size = tree->u.ps - 1;  /* t1 == Op t11 t12 */
     int n11size = t1->u.ps - 1;
     int n12size = n1size - n11size - 1;
     memmove(sib1(tree), sib1(t1), n11size * sizeof(TTree)); /* move t11 */
     tree->u.ps = n11size + 1;
     sib2(tree)->tag = tree->tag;
     sib2(tree)->u.ps = n12size + 1;
   }
 }
 
 
 /*
 ** Make final adjustments in a tree. Fix open calls in tree 't',
 ** making them refer to their respective rules or raising appropriate
 ** errors (if not inside a grammar). Correct associativity of associative
 ** constructions (making them right associative). Assume that tree's
 ** ktable is at the top of the stack (for error messages).
 */
 static void finalfix (lua_State *L, int postable, TTree *g, TTree *t) {
  tailcall:
   switch (t->tag) {
     case TGrammar:  /* subgrammars were already fixed */
       return;
     case TOpenCall: {
       if (g != NULL)  /* inside a grammar? */
         fixonecall(L, postable, g, t);
       else {  /* open call outside grammar */
         lua_rawgeti(L, -1, t->key);
         luaL_error(L, "rule '%s' used outside a grammar", val2str(L, -1));
       }
       break;
     }
     case TSeq: case TChoice:
       correctassociativity(t);
       break;
   }
   switch (numsiblings[t->tag]) {
     case 1: /* finalfix(L, postable, g, sib1(t)); */
       t = sib1(t); goto tailcall;
     case 2:
       finalfix(L, postable, g, sib1(t));
       t = sib2(t); goto tailcall;  /* finalfix(L, postable, g, sib2(t)); */
     default: assert(numsiblings[t->tag] == 0); break;
   }
 }
 
 
 
 /*
 ** {===================================================================
 ** KTable manipulation
 **
 ** - The ktable of a pattern 'p' can be shared by other patterns that
 ** contain 'p' and no other constants. Because of this sharing, we
 ** should not add elements to a 'ktable' unless it was freshly created
 ** for the new pattern.
 **
 ** - The maximum index in a ktable is USHRT_MAX, because trees and
 ** patterns use unsigned shorts to store those indices.
 ** ====================================================================
 */
 
 /*
 ** Create a new 'ktable' to the pattern at the top of the stack.
 */
 static void newktable (lua_State *L, int n) {
   lua_createtable(L, n, 0);  /* create a fresh table */
   lua_setuservalue(L, -2);  /* set it as 'ktable' for pattern */
 }
 
 
 /*
 ** Add element 'idx' to 'ktable' of pattern at the top of the stack;
 ** Return index of new element.
 ** If new element is nil, does not add it to table (as it would be
 ** useless) and returns 0, as ktable[0] is always nil.
 */
 static int addtoktable (lua_State *L, int idx) {
   if (lua_isnil(L, idx))  /* nil value? */
     return 0;
   else {
     int n;
     lua_getuservalue(L, -1);  /* get ktable from pattern */
     n = lua_rawlen(L, -1);
     if (n >= USHRT_MAX)
       luaL_error(L, "too many Lua values in pattern");
     lua_pushvalue(L, idx);  /* element to be added */
     lua_rawseti(L, -2, ++n);
     lua_pop(L, 1);  /* remove 'ktable' */
     return n;
   }
 }
 
 
 /*
 ** Return the number of elements in the ktable at 'idx'.
 ** In Lua 5.2/5.3, default "environment" for patterns is nil, not
 ** a table. Treat it as an empty table. In Lua 5.1, assumes that
 ** the environment has no numeric indices (len == 0)
 */
 static int ktablelen (lua_State *L, int idx) {
   if (!lua_istable(L, idx)) return 0;
   else return lua_rawlen(L, idx);
 }
 
 
 /*
 ** Concatentate the contents of table 'idx1' into table 'idx2'.
 ** (Assume that both indices are negative.)
 ** Return the original length of table 'idx2' (or 0, if no
 ** element was added, as there is no need to correct any index).
 */
 static int concattable (lua_State *L, int idx1, int idx2) {
   int i;
   int n1 = ktablelen(L, idx1);
   int n2 = ktablelen(L, idx2);
   if (n1 + n2 > USHRT_MAX)
     luaL_error(L, "too many Lua values in pattern");
   if (n1 == 0) return 0;  /* nothing to correct */
   for (i = 1; i <= n1; i++) {
     lua_rawgeti(L, idx1, i);
     lua_rawseti(L, idx2 - 1, n2 + i);  /* correct 'idx2' */
   }
   return n2;
 }
 
 
 /*
 ** When joining 'ktables', constants from one of the subpatterns must
 ** be renumbered; 'correctkeys' corrects their indices (adding 'n'
 ** to each of them)
 */
 static void correctkeys (TTree *tree, int n) {
   if (n == 0) return;  /* no correction? */
  tailcall:
   switch (tree->tag) {
     case TOpenCall: case TCall: case TRunTime: case TRule: {
       if (tree->key > 0)
         tree->key += n;
       break;
     }
     case TCapture: {
       if (tree->key > 0 && tree->cap != Carg && tree->cap != Cnum)
         tree->key += n;
       break;
     }
     default: break;
   }
   switch (numsiblings[tree->tag]) {
     case 1:  /* correctkeys(sib1(tree), n); */
       tree = sib1(tree); goto tailcall;
     case 2:
       correctkeys(sib1(tree), n);
       tree = sib2(tree); goto tailcall;  /* correctkeys(sib2(tree), n); */
     default: assert(numsiblings[tree->tag] == 0); break;
   }
 }
 
 
 /*
 ** Join the ktables from p1 and p2 the ktable for the new pattern at the
 ** top of the stack, reusing them when possible.
 */
 static void joinktables (lua_State *L, int p1, TTree *t2, int p2) {
   int n1, n2;
   lua_getuservalue(L, p1);  /* get ktables */
   lua_getuservalue(L, p2);
   n1 = ktablelen(L, -2);
   n2 = ktablelen(L, -1);
   if (n1 == 0 && n2 == 0)  /* are both tables empty? */
     lua_pop(L, 2);  /* nothing to be done; pop tables */
   else if (n2 == 0 || lp_equal(L, -2, -1)) {  /* 2nd table empty or equal? */
     lua_pop(L, 1);  /* pop 2nd table */
     lua_setuservalue(L, -2);  /* set 1st ktable into new pattern */
   }
   else if (n1 == 0) {  /* first table is empty? */
     lua_setuservalue(L, -3);  /* set 2nd table into new pattern */
     lua_pop(L, 1);  /* pop 1st table */
   }
   else {
     lua_createtable(L, n1 + n2, 0);  /* create ktable for new pattern */
     /* stack: new p; ktable p1; ktable p2; new ktable */
     concattable(L, -3, -1);  /* from p1 into new ktable */
     concattable(L, -2, -1);  /* from p2 into new ktable */
     lua_setuservalue(L, -4);  /* new ktable becomes 'p' environment */
     lua_pop(L, 2);  /* pop other ktables */
     correctkeys(t2, n1);  /* correction for indices from p2 */
   }
 }
 
 
 /*
 ** copy 'ktable' of element 'idx' to new tree (on top of stack)
 */
 static void copyktable (lua_State *L, int idx) {
   lua_getuservalue(L, idx);
   lua_setuservalue(L, -2);
 }
 
 
 /*
 ** merge 'ktable' from 'stree' at stack index 'idx' into 'ktable'
 ** from tree at the top of the stack, and correct corresponding
 ** tree.
 */
 static void mergektable (lua_State *L, int idx, TTree *stree) {
   int n;
   lua_getuservalue(L, -1);  /* get ktables */
   lua_getuservalue(L, idx);
   n = concattable(L, -1, -2);
   lua_pop(L, 2);  /* remove both ktables */
   correctkeys(stree, n);
 }
 
 
 /*
 ** Create a new 'ktable' to the pattern at the top of the stack, adding
 ** all elements from pattern 'p' (if not 0) plus element 'idx' to it.
 ** Return index of new element.
 */
 static int addtonewktable (lua_State *L, int p, int idx) {
   newktable(L, 1);
   if (p)
     mergektable(L, p, NULL);
   return addtoktable(L, idx);
 }
 
 /* }====================================================== */
 
 
 /*
 ** {======================================================
 ** Tree generation
 ** =======================================================
 */
 
 /*
 ** In 5.2, could use 'luaL_testudata'...
 */
 static int testpattern (lua_State *L, int idx) {
   if (lua_touserdata(L, idx)) {  /* value is a userdata? */
     if (lua_getmetatable(L, idx)) {  /* does it have a metatable? */
       luaL_getmetatable(L, PATTERN_T);
       if (lua_rawequal(L, -1, -2)) {  /* does it have the correct mt? */
         lua_pop(L, 2);  /* remove both metatables */
         return 1;
       }
     }
   }
   return 0;
 }
 
 
 static Pattern *getpattern (lua_State *L, int idx) {
   return (Pattern *)luaL_checkudata(L, idx, PATTERN_T);
 }
 
 
 static int getsize (lua_State *L, int idx) {
   return (lua_rawlen(L, idx) - sizeof(Pattern)) / sizeof(TTree) + 1;
 }
 
 
 static TTree *gettree (lua_State *L, int idx, int *len) {
   Pattern *p = getpattern(L, idx);
   if (len)
     *len = getsize(L, idx);
   return p->tree;
 }
 
 
 /*
 ** create a pattern. Set its uservalue (the 'ktable') equal to its
 ** metatable. (It could be any empty sequence; the metatable is at
 ** hand here, so we use it.)
 */
 static TTree *newtree (lua_State *L, int len) {
   size_t size = (len - 1) * sizeof(TTree) + sizeof(Pattern);
   Pattern *p = (Pattern *)lua_newuserdata(L, size);
   luaL_getmetatable(L, PATTERN_T);
   lua_pushvalue(L, -1);
   lua_setuservalue(L, -3);
   lua_setmetatable(L, -2);
   p->code = NULL;  p->codesize = 0;
   return p->tree;
 }
 
 
 static TTree *newleaf (lua_State *L, int tag) {
   TTree *tree = newtree(L, 1);
   tree->tag = tag;
   return tree;
 }
 
 
 static TTree *newcharset (lua_State *L) {
   TTree *tree = newtree(L, bytes2slots(CHARSETSIZE) + 1);
   tree->tag = TSet;
   loopset(i, treebuffer(tree)[i] = 0);
   return tree;
 }
 
 
 /*
 ** add to tree a sequence where first sibling is 'sib' (with size
 ** 'sibsize'); returns position for second sibling
 */
 static TTree *seqaux (TTree *tree, TTree *sib, int sibsize) {
   tree->tag = TSeq; tree->u.ps = sibsize + 1;
   memcpy(sib1(tree), sib, sibsize * sizeof(TTree));
   return sib2(tree);
 }
 
 
 /*
 ** Build a sequence of 'n' nodes, each with tag 'tag' and 'u.n' got
 ** from the array 's' (or 0 if array is NULL). (TSeq is binary, so it
 ** must build a sequence of sequence of sequence...)
 */
 static void fillseq (TTree *tree, int tag, int n, const char *s) {
   int i;
   for (i = 0; i < n - 1; i++) {  /* initial n-1 copies of Seq tag; Seq ... */
     tree->tag = TSeq; tree->u.ps = 2;
     sib1(tree)->tag = tag;
     sib1(tree)->u.n = s ? (byte)s[i] : 0;
     tree = sib2(tree);
   }
   tree->tag = tag;  /* last one does not need TSeq */
   tree->u.n = s ? (byte)s[i] : 0;
 }
 
 
 /*
 ** Numbers as patterns:
 ** 0 == true (always match); n == TAny repeated 'n' times;
 ** -n == not (TAny repeated 'n' times)
 */
 static TTree *numtree (lua_State *L, int n) {
   if (n == 0)
     return newleaf(L, TTrue);
   else {
     TTree *tree, *nd;
     if (n > 0)
       tree = nd = newtree(L, 2 * n - 1);
     else {  /* negative: code it as !(-n) */
       n = -n;
       tree = newtree(L, 2 * n);
       tree->tag = TNot;
       nd = sib1(tree);
     }
     fillseq(nd, TAny, n, NULL);  /* sequence of 'n' any's */
     return tree;
   }
 }
 
 
 /*
 ** Convert value at index 'idx' to a pattern
 */
 static TTree *getpatt (lua_State *L, int idx, int *len) {
   TTree *tree;
   switch (lua_type(L, idx)) {
     case LUA_TSTRING: {
       size_t slen;
       const char *s = lua_tolstring(L, idx, &slen);  /* get string */
       if (slen == 0)  /* empty? */
         tree = newleaf(L, TTrue);  /* always match */
       else {
         tree = newtree(L, 2 * (slen - 1) + 1);
         fillseq(tree, TChar, slen, s);  /* sequence of 'slen' chars */
       }
       break;
     }
     case LUA_TNUMBER: {
       int n = lua_tointeger(L, idx);
       tree = numtree(L, n);
       break;
     }
     case LUA_TBOOLEAN: {
       tree = (lua_toboolean(L, idx) ? newleaf(L, TTrue) : newleaf(L, TFalse));
       break;
     }
     case LUA_TTABLE: {
       tree = newgrammar(L, idx);
       break;
     }
     case LUA_TFUNCTION: {
       tree = newtree(L, 2);
       tree->tag = TRunTime;
       tree->key = addtonewktable(L, 0, idx);
       sib1(tree)->tag = TTrue;
       break;
     }
     default: {
       return gettree(L, idx, len);
     }
   }
   lua_replace(L, idx);  /* put new tree into 'idx' slot */
   if (len)
     *len = getsize(L, idx);
   return tree;
 }
 
 
 /*
 ** create a new tree, whith a new root and one sibling.
 ** Sibling must be on the Lua stack, at index 1.
 */
 static TTree *newroot1sib (lua_State *L, int tag) {
   int s1;
   TTree *tree1 = getpatt(L, 1, &s1);
   TTree *tree = newtree(L, 1 + s1);  /* create new tree */
   tree->tag = tag;
   memcpy(sib1(tree), tree1, s1 * sizeof(TTree));
   copyktable(L, 1);
   return tree;
 }
 
 
 /*
 ** create a new tree, whith a new root and 2 siblings.
 ** Siblings must be on the Lua stack, first one at index 1.
 */
 static TTree *newroot2sib (lua_State *L, int tag) {
   int s1, s2;
   TTree *tree1 = getpatt(L, 1, &s1);
   TTree *tree2 = getpatt(L, 2, &s2);
   TTree *tree = newtree(L, 1 + s1 + s2);  /* create new tree */
   tree->tag = tag;
   tree->u.ps =  1 + s1;
   memcpy(sib1(tree), tree1, s1 * sizeof(TTree));
   memcpy(sib2(tree), tree2, s2 * sizeof(TTree));
   joinktables(L, 1, sib2(tree), 2);
   return tree;
 }
 
 
 static int lp_P (lua_State *L) {
   luaL_checkany(L, 1);
   getpatt(L, 1, NULL);
   lua_settop(L, 1);
   return 1;
 }
 
 
 /*
 ** sequence operator; optimizations:
 ** false x => false, x true => x, true x => x
 ** (cannot do x . false => false because x may have runtime captures)
 */
 static int lp_seq (lua_State *L) {
   TTree *tree1 = getpatt(L, 1, NULL);
   TTree *tree2 = getpatt(L, 2, NULL);
   if (tree1->tag == TFalse || tree2->tag == TTrue)
     lua_pushvalue(L, 1);  /* false . x == false, x . true = x */
   else if (tree1->tag == TTrue)
     lua_pushvalue(L, 2);  /* true . x = x */
   else
     newroot2sib(L, TSeq);
   return 1;
 }
 
 
 /*
 ** choice operator; optimizations:
 ** charset / charset => charset
 ** true / x => true, x / false => x, false / x => x
 ** (x / true is not equivalent to true)
 */
 static int lp_choice (lua_State *L) {
   Charset st1, st2;
   TTree *t1 = getpatt(L, 1, NULL);
   TTree *t2 = getpatt(L, 2, NULL);
   if (tocharset(t1, &st1) && tocharset(t2, &st2)) {
     TTree *t = newcharset(L);
     loopset(i, treebuffer(t)[i] = st1.cs[i] | st2.cs[i]);
   }
   else if (nofail(t1) || t2->tag == TFalse)
     lua_pushvalue(L, 1);  /* true / x => true, x / false => x */
   else if (t1->tag == TFalse)
     lua_pushvalue(L, 2);  /* false / x => x */
   else
     newroot2sib(L, TChoice);
   return 1;
 }
 
 
 /*
 ** p^n
 */
 static int lp_star (lua_State *L) {
   int size1;
   int n = (int)luaL_checkinteger(L, 2);
   TTree *tree1 = getpatt(L, 1, &size1);
   if (n >= 0) {  /* seq tree1 (seq tree1 ... (seq tree1 (rep tree1))) */
     TTree *tree = newtree(L, (n + 1) * (size1 + 1));
     if (nullable(tree1))
       luaL_error(L, "loop body may accept empty string");
     while (n--)  /* repeat 'n' times */
       tree = seqaux(tree, tree1, size1);
     tree->tag = TRep;
     memcpy(sib1(tree), tree1, size1 * sizeof(TTree));
   }
   else {  /* choice (seq tree1 ... choice tree1 true ...) true */
     TTree *tree;
     n = -n;
     /* size = (choice + seq + tree1 + true) * n, but the last has no seq */
     tree = newtree(L, n * (size1 + 3) - 1);
     for (; n > 1; n--) {  /* repeat (n - 1) times */
       tree->tag = TChoice; tree->u.ps = n * (size1 + 3) - 2;
       sib2(tree)->tag = TTrue;
       tree = sib1(tree);
       tree = seqaux(tree, tree1, size1);
     }
     tree->tag = TChoice; tree->u.ps = size1 + 1;
     sib2(tree)->tag = TTrue;
     memcpy(sib1(tree), tree1, size1 * sizeof(TTree));
   }
   copyktable(L, 1);
   return 1;
 }
 
 
 /*
 ** #p == &p
 */
 static int lp_and (lua_State *L) {
   newroot1sib(L, TAnd);
   return 1;
 }
 
 
 /*
 ** -p == !p
 */
 static int lp_not (lua_State *L) {
   newroot1sib(L, TNot);
   return 1;
 }
 
 
 /*
 ** [t1 - t2] == Seq (Not t2) t1
 ** If t1 and t2 are charsets, make their difference.
 */
 static int lp_sub (lua_State *L) {
   Charset st1, st2;
   int s1, s2;
   TTree *t1 = getpatt(L, 1, &s1);
   TTree *t2 = getpatt(L, 2, &s2);
   if (tocharset(t1, &st1) && tocharset(t2, &st2)) {
     TTree *t = newcharset(L);
     loopset(i, treebuffer(t)[i] = st1.cs[i] & ~st2.cs[i]);
   }
   else {
     TTree *tree = newtree(L, 2 + s1 + s2);
     tree->tag = TSeq;  /* sequence of... */
     tree->u.ps =  2 + s2;
     sib1(tree)->tag = TNot;  /* ...not... */
     memcpy(sib1(sib1(tree)), t2, s2 * sizeof(TTree));  /* ...t2 */
     memcpy(sib2(tree), t1, s1 * sizeof(TTree));  /* ... and t1 */
     joinktables(L, 1, sib1(tree), 2);
   }
   return 1;
 }
 
 
 static int lp_set (lua_State *L) {
   size_t l;
   const char *s = luaL_checklstring(L, 1, &l);
   TTree *tree = newcharset(L);
   while (l--) {
     setchar(treebuffer(tree), (byte)(*s));
     s++;
   }
   return 1;
 }
 
 
 static int lp_range (lua_State *L) {
   int arg;
   int top = lua_gettop(L);
   TTree *tree = newcharset(L);
   for (arg = 1; arg <= top; arg++) {
     int c;
     size_t l;
     const char *r = luaL_checklstring(L, arg, &l);
     luaL_argcheck(L, l == 2, arg, "range must have two characters");
     for (c = (byte)r[0]; c <= (byte)r[1]; c++)
       setchar(treebuffer(tree), c);
   }
   return 1;
 }
 
 
 /*
 ** Look-behind predicate
 */
 static int lp_behind (lua_State *L) {
   TTree *tree;
   TTree *tree1 = getpatt(L, 1, NULL);
   int n = fixedlen(tree1);
   luaL_argcheck(L, n >= 0, 1, "pattern may not have fixed length");
   luaL_argcheck(L, !hascaptures(tree1), 1, "pattern have captures");
   luaL_argcheck(L, n <= MAXBEHIND, 1, "pattern too long to look behind");
   tree = newroot1sib(L, TBehind);
   tree->u.n = n;
   return 1;
 }
 
 
 /*
 ** Create a non-terminal
 */
 static int lp_V (lua_State *L) {
   TTree *tree = newleaf(L, TOpenCall);
   luaL_argcheck(L, !lua_isnoneornil(L, 1), 1, "non-nil value expected");
   tree->key = addtonewktable(L, 0, 1);
   return 1;
 }
 
 
 /*
 ** Create a tree for a non-empty capture, with a body and
 ** optionally with an associated Lua value (at index 'labelidx' in the
 ** stack)
 */
 static int capture_aux (lua_State *L, int cap, int labelidx) {
   TTree *tree = newroot1sib(L, TCapture);
   tree->cap = cap;
   tree->key = (labelidx == 0) ? 0 : addtonewktable(L, 1, labelidx);
   return 1;
 }
 
 
 /*
 ** Fill a tree with an empty capture, using an empty (TTrue) sibling.
 */
 static TTree *auxemptycap (TTree *tree, int cap) {
   tree->tag = TCapture;
   tree->cap = cap;
   sib1(tree)->tag = TTrue;
   return tree;
 }
 
 
 /*
 ** Create a tree for an empty capture
 */
 static TTree *newemptycap (lua_State *L, int cap) {
   return auxemptycap(newtree(L, 2), cap);
 }
 
 
 /*
 ** Create a tree for an empty capture with an associated Lua value
 */
 static TTree *newemptycapkey (lua_State *L, int cap, int idx) {
   TTree *tree = auxemptycap(newtree(L, 2), cap);
   tree->key = addtonewktable(L, 0, idx);
   return tree;
 }
 
 
 /*
 ** Captures with syntax p / v
 ** (function capture, query capture, string capture, or number capture)
 */
 static int lp_divcapture (lua_State *L) {
   switch (lua_type(L, 2)) {
     case LUA_TFUNCTION: return capture_aux(L, Cfunction, 2);
     case LUA_TTABLE: return capture_aux(L, Cquery, 2);
     case LUA_TSTRING: return capture_aux(L, Cstring, 2);
     case LUA_TNUMBER: {
       int n = lua_tointeger(L, 2);
       TTree *tree = newroot1sib(L, TCapture);
       luaL_argcheck(L, 0 <= n && n <= SHRT_MAX, 1, "invalid number");
       tree->cap = Cnum;
       tree->key = n;
       return 1;
     }
     default: return luaL_argerror(L, 2, "invalid replacement value");
   }
 }
 
 
 static int lp_substcapture (lua_State *L) {
   return capture_aux(L, Csubst, 0);
 }
 
 
 static int lp_tablecapture (lua_State *L) {
   return capture_aux(L, Ctable, 0);
 }
 
 
 static int lp_groupcapture (lua_State *L) {
   if (lua_isnoneornil(L, 2))
     return capture_aux(L, Cgroup, 0);
   else
     return capture_aux(L, Cgroup, 2);
 }
 
 
 static int lp_foldcapture (lua_State *L) {
   luaL_checktype(L, 2, LUA_TFUNCTION);
   return capture_aux(L, Cfold, 2);
 }
 
 
 static int lp_simplecapture (lua_State *L) {
   return capture_aux(L, Csimple, 0);
 }
 
 
 static int lp_poscapture (lua_State *L) {
   newemptycap(L, Cposition);
   return 1;
 }
 
 
 static int lp_argcapture (lua_State *L) {
   int n = (int)luaL_checkinteger(L, 1);
   TTree *tree = newemptycap(L, Carg);
   tree->key = n;
   luaL_argcheck(L, 0 < n && n <= SHRT_MAX, 1, "invalid argument index");
   return 1;
 }
 
 
 static int lp_backref (lua_State *L) {
   luaL_checkany(L, 1);
   newemptycapkey(L, Cbackref, 1);
   return 1;
 }
 
 
 /*
 ** Constant capture
 */
 static int lp_constcapture (lua_State *L) {
   int i;
   int n = lua_gettop(L);  /* number of values */
   if (n == 0)  /* no values? */
     newleaf(L, TTrue);  /* no capture */
   else if (n == 1)
     newemptycapkey(L, Cconst, 1);  /* single constant capture */
   else {  /* create a group capture with all values */
     TTree *tree = newtree(L, 1 + 3 * (n - 1) + 2);
     newktable(L, n);  /* create a 'ktable' for new tree */
     tree->tag = TCapture;
     tree->cap = Cgroup;
     tree->key = 0;
     tree = sib1(tree);
     for (i = 1; i <= n - 1; i++) {
       tree->tag = TSeq;
       tree->u.ps = 3;  /* skip TCapture and its sibling */
       auxemptycap(sib1(tree), Cconst);
       sib1(tree)->key = addtoktable(L, i);
       tree = sib2(tree);
     }
     auxemptycap(tree, Cconst);
     tree->key = addtoktable(L, i);
   }
   return 1;
 }
 
 
 static int lp_matchtime (lua_State *L) {
   TTree *tree;
   luaL_checktype(L, 2, LUA_TFUNCTION);
   tree = newroot1sib(L, TRunTime);
   tree->key = addtonewktable(L, 1, 2);
   return 1;
 }
 
 /* }====================================================== */
 
 
 /*
 ** {======================================================
 ** Grammar - Tree generation
 ** =======================================================
 */
 
 /*
 ** push on the stack the index and the pattern for the
 ** initial rule of grammar at index 'arg' in the stack;
 ** also add that index into position table.
 */
 static void getfirstrule (lua_State *L, int arg, int postab) {
   lua_rawgeti(L, arg, 1);  /* access first element */
   if (lua_isstring(L, -1)) {  /* is it the name of initial rule? */
     lua_pushvalue(L, -1);  /* duplicate it to use as key */
     lua_gettable(L, arg);  /* get associated rule */
   }
   else {
     lua_pushinteger(L, 1);  /* key for initial rule */
     lua_insert(L, -2);  /* put it before rule */
   }
   if (!testpattern(L, -1)) {  /* initial rule not a pattern? */
     if (lua_isnil(L, -1))
       luaL_error(L, "grammar has no initial rule");
     else
       luaL_error(L, "initial rule '%s' is not a pattern", lua_tostring(L, -2));
   }
   lua_pushvalue(L, -2);  /* push key */
   lua_pushinteger(L, 1);  /* push rule position (after TGrammar) */
   lua_settable(L, postab);  /* insert pair at position table */
 }
 
 /*
 ** traverse grammar at index 'arg', pushing all its keys and patterns
 ** into the stack. Create a new table (before all pairs key-pattern) to
 ** collect all keys and their associated positions in the final tree
 ** (the "position table").
 ** Return the number of rules and (in 'totalsize') the total size
 ** for the new tree.
 */
 static int collectrules (lua_State *L, int arg, int *totalsize) {
   int n = 1;  /* to count number of rules */
   int postab = lua_gettop(L) + 1;  /* index of position table */
   int size;  /* accumulator for total size */
   lua_newtable(L);  /* create position table */
   getfirstrule(L, arg, postab);
   size = 2 + getsize(L, postab + 2);  /* TGrammar + TRule + rule */
   lua_pushnil(L);  /* prepare to traverse grammar table */
   while (lua_next(L, arg) != 0) {
     if (lua_tonumber(L, -2) == 1 ||
         lp_equal(L, -2, postab + 1)) {  /* initial rule? */
       lua_pop(L, 1);  /* remove value (keep key for lua_next) */
       continue;
     }
     if (!testpattern(L, -1))  /* value is not a pattern? */
       luaL_error(L, "rule '%s' is not a pattern", val2str(L, -2));
     luaL_checkstack(L, LUA_MINSTACK, "grammar has too many rules");
     lua_pushvalue(L, -2);  /* push key (to insert into position table) */
     lua_pushinteger(L, size);
     lua_settable(L, postab);
     size += 1 + getsize(L, -1);  /* update size */
     lua_pushvalue(L, -2);  /* push key (for next lua_next) */
     n++;
   }
   *totalsize = size + 1;  /* TTrue to finish list of rules */
   return n;
 }
 
 
 static void buildgrammar (lua_State *L, TTree *grammar, int frule, int n) {
   int i;
   TTree *nd = sib1(grammar);  /* auxiliary pointer to traverse the tree */
   for (i = 0; i < n; i++) {  /* add each rule into new tree */
     int ridx = frule + 2*i + 1;  /* index of i-th rule */
     int rulesize;
     TTree *rn = gettree(L, ridx, &rulesize);
     nd->tag = TRule;
     nd->key = 0;  /* will be fixed when rule is used */
     nd->cap = i;  /* rule number */
     nd->u.ps = rulesize + 1;  /* point to next rule */
     memcpy(sib1(nd), rn, rulesize * sizeof(TTree));  /* copy rule */
     mergektable(L, ridx, sib1(nd));  /* merge its ktable into new one */
     nd = sib2(nd);  /* move to next rule */
   }
   nd->tag = TTrue;  /* finish list of rules */
 }
 
 
 /*
 ** Check whether a tree has potential infinite loops
 */
 static int checkloops (TTree *tree) {
  tailcall:
   if (tree->tag == TRep && nullable(sib1(tree)))
     return 1;
   else if (tree->tag == TGrammar)
     return 0;  /* sub-grammars already checked */
   else {
     switch (numsiblings[tree->tag]) {
       case 1:  /* return checkloops(sib1(tree)); */
         tree = sib1(tree); goto tailcall;
       case 2:
         if (checkloops(sib1(tree))) return 1;
         /* else return checkloops(sib2(tree)); */
         tree = sib2(tree); goto tailcall;
       default: assert(numsiblings[tree->tag] == 0); return 0;
     }
   }
 }
 
 
 /*
 ** Give appropriate error message for 'verifyrule'. If a rule appears
 ** twice in 'passed', there is path from it back to itself without
 ** advancing the subject.
 */
 static int verifyerror (lua_State *L, int *passed, int npassed) {
   int i, j;
   for (i = npassed - 1; i >= 0; i--) {  /* search for a repetition */
     for (j = i - 1; j >= 0; j--) {
       if (passed[i] == passed[j]) {
         lua_rawgeti(L, -1, passed[i]);  /* get rule's key */
         return luaL_error(L, "rule '%s' may be left recursive", val2str(L, -1));
       }
     }
   }
   return luaL_error(L, "too many left calls in grammar");
 }
 
 
 /*
 ** Check whether a rule can be left recursive; raise an error in that
 ** case; otherwise return 1 iff pattern is nullable.
 ** The return value is used to check sequences, where the second pattern
 ** is only relevant if the first is nullable.
 ** Parameter 'nb' works as an accumulator, to allow tail calls in
 ** choices. ('nb' true makes function returns true.)
 ** Parameter 'passed' is a list of already visited rules, 'npassed'
 ** counts the elements in 'passed'.
 ** Assume ktable at the top of the stack.
 */
 static int verifyrule (lua_State *L, TTree *tree, int *passed, int npassed,
                        int nb) {
  tailcall:
   switch (tree->tag) {
     case TChar: case TSet: case TAny:
     case TFalse:
       return nb;  /* cannot pass from here */
     case TTrue:
     case TBehind:  /* look-behind cannot have calls */
       return 1;
     case TNot: case TAnd: case TRep:
       /* return verifyrule(L, sib1(tree), passed, npassed, 1); */
       tree = sib1(tree); nb = 1; goto tailcall;
     case TCapture: case TRunTime:
       /* return verifyrule(L, sib1(tree), passed, npassed, nb); */
       tree = sib1(tree); goto tailcall;
     case TCall:
       /* return verifyrule(L, sib2(tree), passed, npassed, nb); */
       tree = sib2(tree); goto tailcall;
     case TSeq:  /* only check 2nd child if first is nb */
       if (!verifyrule(L, sib1(tree), passed, npassed, 0))
         return nb;
       /* else return verifyrule(L, sib2(tree), passed, npassed, nb); */
       tree = sib2(tree); goto tailcall;
     case TChoice:  /* must check both children */
       nb = verifyrule(L, sib1(tree), passed, npassed, nb);
       /* return verifyrule(L, sib2(tree), passed, npassed, nb); */
       tree = sib2(tree); goto tailcall;
     case TRule:
       if (npassed >= MAXRULES)
         return verifyerror(L, passed, npassed);
       else {
         passed[npassed++] = tree->key;
         /* return verifyrule(L, sib1(tree), passed, npassed); */
         tree = sib1(tree); goto tailcall;
       }
     case TGrammar:
       return nullable(tree);  /* sub-grammar cannot be left recursive */
     default: assert(0); return 0;
   }
 }
 
 
 static void verifygrammar (lua_State *L, TTree *grammar) {
   int passed[MAXRULES];
   TTree *rule;
   /* check left-recursive rules */
   for (rule = sib1(grammar); rule->tag == TRule; rule = sib2(rule)) {
     if (rule->key == 0) continue;  /* unused rule */
     verifyrule(L, sib1(rule), passed, 0, 0);
   }
   assert(rule->tag == TTrue);
   /* check infinite loops inside rules */
   for (rule = sib1(grammar); rule->tag == TRule; rule = sib2(rule)) {
     if (rule->key == 0) continue;  /* unused rule */
     if (checkloops(sib1(rule))) {
       lua_rawgeti(L, -1, rule->key);  /* get rule's key */
       luaL_error(L, "empty loop in rule '%s'", val2str(L, -1));
     }
   }
   assert(rule->tag == TTrue);
 }
 
 
 /*
 ** Give a name for the initial rule if it is not referenced
 */
 static void initialrulename (lua_State *L, TTree *grammar, int frule) {
   if (sib1(grammar)->key == 0) {  /* initial rule is not referenced? */
     int n = lua_rawlen(L, -1) + 1;  /* index for name */
     lua_pushvalue(L, frule);  /* rule's name */
     lua_rawseti(L, -2, n);  /* ktable was on the top of the stack */
     sib1(grammar)->key = n;
   }
 }
 
 
 static TTree *newgrammar (lua_State *L, int arg) {
   int treesize;
   int frule = lua_gettop(L) + 2;  /* position of first rule's key */
   int n = collectrules(L, arg, &treesize);
   TTree *g = newtree(L, treesize);
   luaL_argcheck(L, n <= MAXRULES, arg, "grammar has too many rules");
   g->tag = TGrammar;  g->u.n = n;
   lua_newtable(L);  /* create 'ktable' */
   lua_setuservalue(L, -2);
   buildgrammar(L, g, frule, n);
   lua_getuservalue(L, -1);  /* get 'ktable' for new tree */
   finalfix(L, frule - 1, g, sib1(g));
   initialrulename(L, g, frule);
   verifygrammar(L, g);
   lua_pop(L, 1);  /* remove 'ktable' */
   lua_insert(L, -(n * 2 + 2));  /* move new table to proper position */
   lua_pop(L, n * 2 + 1);  /* remove position table + rule pairs */
   return g;  /* new table at the top of the stack */
 }
 
 /* }====================================================== */
 
 
 static Instruction *prepcompile (lua_State *L, Pattern *p, int idx) {
   lua_getuservalue(L, idx);  /* push 'ktable' (may be used by 'finalfix') */
   finalfix(L, 0, NULL, p->tree);
   lua_pop(L, 1);  /* remove 'ktable' */
   return compile(L, p);
 }
 
 
 static int lp_printtree (lua_State *L) {
   TTree *tree = getpatt(L, 1, NULL);
   int c = lua_toboolean(L, 2);
   if (c) {
     lua_getuservalue(L, 1);  /* push 'ktable' (may be used by 'finalfix') */
     finalfix(L, 0, NULL, tree);
     lua_pop(L, 1);  /* remove 'ktable' */
   }
   printktable(L, 1);
   printtree(tree, 0);
   return 0;
 }
 
 
 static int lp_printcode (lua_State *L) {
   Pattern *p = getpattern(L, 1);
   printktable(L, 1);
   if (p->code == NULL)  /* not compiled yet? */
     prepcompile(L, p, 1);
   printpatt(p->code, p->codesize);
   return 0;
 }
 
 
 /*
 ** Get the initial position for the match, interpreting negative
 ** values from the end of the subject
 */
 static size_t initposition (lua_State *L, size_t len) {
   lua_Integer ii = luaL_optinteger(L, 3, 1);
   if (ii > 0) {  /* positive index? */
     if ((size_t)ii <= len)  /* inside the string? */
       return (size_t)ii - 1;  /* return it (corrected to 0-base) */
     else return len;  /* crop at the end */
   }
   else {  /* negative index */
     if ((size_t)(-ii) <= len)  /* inside the string? */
       return len - ((size_t)(-ii));  /* return position from the end */
     else return 0;  /* crop at the beginning */
   }
 }
 
 
 /*
 ** Main match function
 */
 static int lp_match (lua_State *L) {
   Capture capture[INITCAPSIZE];
   const char *r;
   size_t l;
   Pattern *p = (getpatt(L, 1, NULL), getpattern(L, 1));
   Instruction *code = (p->code != NULL) ? p->code : prepcompile(L, p, 1);
   const char *s = luaL_checklstring(L, SUBJIDX, &l);
   size_t i = initposition(L, l);
   int ptop = lua_gettop(L);
   lua_pushnil(L);  /* initialize subscache */
   lua_pushlightuserdata(L, capture);  /* initialize caplistidx */
   lua_getuservalue(L, 1);  /* initialize penvidx */
   r = match(L, s, s + i, s + l, code, capture, ptop);
   if (r == NULL) {
     lua_pushnil(L);
     return 1;
   }
   return getcaptures(L, s, r, ptop);
 }
 
 
 
 /*
 ** {======================================================
 ** Library creation and functions not related to matching
 ** =======================================================
 */
 
 /* maximum limit for stack size */
 #define MAXLIM		(INT_MAX / 100)
 
 static int lp_setmax (lua_State *L) {
   lua_Integer lim = luaL_checkinteger(L, 1);
   luaL_argcheck(L, 0 < lim && lim <= MAXLIM, 1, "out of range");
   lua_settop(L, 1);
   lua_setfield(L, LUA_REGISTRYINDEX, MAXSTACKIDX);
   return 0;
 }
 
 
 static int lp_version (lua_State *L) {
   lua_pushstring(L, VERSION);
   return 1;
 }
 
 
 static int lp_type (lua_State *L) {
   if (testpattern(L, 1))
     lua_pushliteral(L, "pattern");
   else
     lua_pushnil(L);
   return 1;
 }
 
 
 int lp_gc (lua_State *L) {
   Pattern *p = getpattern(L, 1);
   realloccode(L, p, 0);  /* delete code block */
   return 0;
 }
 
 
 static void createcat (lua_State *L, const char *catname, int (catf) (int)) {
   TTree *t = newcharset(L);
   int i;
   for (i = 0; i <= UCHAR_MAX; i++)
     if (catf(i)) setchar(treebuffer(t), i);
   lua_setfield(L, -2, catname);
 }
 
 
 static int lp_locale (lua_State *L) {
   if (lua_isnoneornil(L, 1)) {
     lua_settop(L, 0);
     lua_createtable(L, 0, 12);
   }
   else {
     luaL_checktype(L, 1, LUA_TTABLE);
     lua_settop(L, 1);
   }
   createcat(L, "alnum", isalnum);
   createcat(L, "alpha", isalpha);
   createcat(L, "cntrl", iscntrl);
   createcat(L, "digit", isdigit);
   createcat(L, "graph", isgraph);
   createcat(L, "lower", islower);
   createcat(L, "print", isprint);
   createcat(L, "punct", ispunct);
   createcat(L, "space", isspace);
   createcat(L, "upper", isupper);
   createcat(L, "xdigit", isxdigit);
   return 1;
 }
 
 
 static struct luaL_Reg pattreg[] = {
   {"ptree", lp_printtree},
   {"pcode", lp_printcode},
   {"match", lp_match},
   {"B", lp_behind},
   {"V", lp_V},
   {"C", lp_simplecapture},
   {"Cc", lp_constcapture},
   {"Cmt", lp_matchtime},
   {"Cb", lp_backref},
   {"Carg", lp_argcapture},
   {"Cp", lp_poscapture},
   {"Cs", lp_substcapture},
   {"Ct", lp_tablecapture},
   {"Cf", lp_foldcapture},
   {"Cg", lp_groupcapture},
   {"P", lp_P},
   {"S", lp_set},
   {"R", lp_range},
   {"locale", lp_locale},
   {"version", lp_version},
   {"setmaxstack", lp_setmax},
   {"type", lp_type},
   {NULL, NULL}
 };
 
 
 static struct luaL_Reg metareg[] = {
   {"__mul", lp_seq},
   {"__add", lp_choice},
   {"__pow", lp_star},
   {"__gc", lp_gc},
   {"__len", lp_and},
   {"__div", lp_divcapture},
   {"__unm", lp_not},
   {"__sub", lp_sub},
   {NULL, NULL}
 };
 
 
 int luaopen_lpeg (lua_State *L);
 int luaopen_lpeg (lua_State *L) {
   luaL_newmetatable(L, PATTERN_T);
   lua_pushnumber(L, MAXBACK);  /* initialize maximum backtracking */
   lua_setfield(L, LUA_REGISTRYINDEX, MAXSTACKIDX);
   luaL_setfuncs(L, metareg, 0);
   luaL_newlib(L, pattreg);
   lua_pushvalue(L, -1);
   lua_setfield(L, -3, "__index");
   return 1;
 }
 
 /* }====================================================== */