common.w

模拟器提供了一个简单易用的平台

  }
}

@ @<If the current line starts with \.{@@y}...@>=
if (buffer[1]=='x' || buffer[1]=='z') {
  loc=buffer+2; err_print("! Where is the matching @@y?");
@.Where is the match...@>
  }
else if (buffer[1]=='y') {
  if (n>0) {
    loc=buffer+2;
    printf("\n! Hmm... %d ",n);
    err_print("of the preceding lines failed to match");
@.Hmm... n of the preceding...@>
  }
  change_depth=include_depth;
  return;
}

@ The |reset_input| procedure, which gets \.{CWEB} ready to read the
user's \.{CWEB} input, is used at the beginning of phase one of \.{CTANGLE},
phases one and two of \.{CWEAVE}.

@c
void
reset_input()
{
  limit=buffer; loc=buffer+1; buffer[0]=' ';
  @<Open input files@>;
  include_depth=0; cur_line=0; change_line=0;
  change_depth=include_depth;
  changing=1; prime_the_change_buffer(); changing=!changing;
  limit=buffer; loc=buffer+1; buffer[0]=' '; input_has_ended=0;
}

@ The following code opens the input files.
@^system dependencies@>

@<Open input files@>=
if ((web_file=fopen(web_file_name,"r"))==NULL) {
  strcpy(web_file_name,alt_web_file_name);
  if ((web_file=fopen(web_file_name,"r"))==NULL)
       fatal("! Cannot open input file ", web_file_name);
}
@.Cannot open input file@>
@.Cannot open change file@>
web_file_open=1;
if ((change_file=fopen(change_file_name,"r"))==NULL)
       fatal("! Cannot open change file ", change_file_name);

@ The |get_line| procedure is called when |loc>limit|; it puts the next
line of merged input into the buffer and updates the other variables
appropriately. A space is placed at the right end of the line.
This procedure returns |!input_has_ended| because we often want to
check the value of that variable after calling the procedure.

If we've just changed from the |cur_file| to the |change_file|, or if
the |cur_file| has changed, we tell \.{CTANGLE} to print this
information in the \CEE/ file by means of the |print_where| flag.

@d max_sections 2000 /* number of identifiers, strings, section names;
  must be less than 10240 */

@<Defin...@>=
typedef unsigned short sixteen_bits;
sixteen_bits section_count; /* the current section number */
boolean changed_section[max_sections]; /* is the section changed? */
boolean change_pending; /* if the current change is not yet recorded in
  |changed_section[section_count]| */
boolean print_where=0; /* should \.{CTANGLE} print line and file info? */

@ @c
int get_line() /* inputs the next line */
{
  restart:
  if (changing && include_depth==change_depth)
   @<Read from |change_file| and maybe turn off |changing|@>;
  if (! changing || include_depth>change_depth) {
    @<Read from |cur_file| and maybe turn on |changing|@>;
    if (changing && include_depth==change_depth) goto restart;
  }
  loc=buffer; *limit=' ';
  if (*buffer=='@@' && (*(buffer+1)=='i' || *(buffer+1)=='I')) {
    loc=buffer+2;
    while (loc<=limit && (*loc==' '||*loc=='\t'||*loc=='"')) loc++;
    if (loc>=limit) {
      err_print("! Include file name not given");
@.Include file name ...@>
      goto restart;
    }
    if (include_depth>=max_include_depth-1) {
      err_print("! Too many nested includes");
@.Too many nested includes@>
      goto restart;
    }
    include_depth++; /* push input stack */
    @<Try to open include file, abort push if unsuccessful, go to |restart|@>;
  }
  return (!input_has_ended);
}

@ When an \.{@@i} line is found in the |cur_file|, we must temporarily
stop reading it and start reading from the named include file.  The
\.{@@i} line should give a complete file name with or without
double quotes.
If the environment variable \.{CWEBINPUTS} is set, or if the compiler flag
of the same name was defined at compile time,
\.{CWEB} will look for include files in the directory thus named, if
it cannot find them in the current directory.
(Colon-separated paths are not supported.)
The remainder of the \.{@@i} line after the file name is ignored.

@d too_long() {include_depth--;
        err_print("! Include file name too long"); goto restart;}

@<Include...@>=
#include <stdlib.h> /* declaration of |getenv| and |exit| */

@ @<Try to open...@>= {
  char temp_file_name[max_file_name_length];
  char *cur_file_name_end=cur_file_name+max_file_name_length-1;
  char *k=cur_file_name, *kk;
  int l; /* length of file name */

  while (*loc!=' '&&*loc!='\t'&&*loc!='"'&&k<=cur_file_name_end) *k++=*loc++;
  if (k>cur_file_name_end) too_long();
@.Include file name ...@>
  *k='\0';
  if ((cur_file=fopen(cur_file_name,"r"))!=NULL) {
    cur_line=0; print_where=1;
    goto restart; /* success */
  }
  kk=getenv("CWEBINPUTS");
  if (kk!=NULL) {
    if ((l=strlen(kk))>max_file_name_length-2) too_long();
    strcpy(temp_file_name,kk);
  }
  else {
#ifdef CWEBINPUTS
    if ((l=strlen(CWEBINPUTS))>max_file_name_length-2) too_long();
    strcpy(temp_file_name,CWEBINPUTS);
#else
    l=0;
#endif /* |CWEBINPUTS| */
  }
  if (l>0) {
    if (k+l+2>=cur_file_name_end)  too_long();
@.Include file name ...@>
    for (; k>= cur_file_name; k--) *(k+l+1)=*k;
    strcpy(cur_file_name,temp_file_name);
    cur_file_name[l]='/'; /* \UNIX/ pathname separator */
    if ((cur_file=fopen(cur_file_name,"r"))!=NULL) {
      cur_line=0; print_where=1;
      goto restart; /* success */
    }
  }
  include_depth--; err_print("! Cannot open include file"); goto restart;
}

@ @<Read from |cur_file|...@>= {
  cur_line++;
  while (!input_ln(cur_file)) { /* pop the stack or quit */
    print_where=1;
    if (include_depth==0) {input_has_ended=1; break;}
    else {
      fclose(cur_file); include_depth--;
      if (changing && include_depth==change_depth) break;
      cur_line++;
    }
  }
  if (!changing && !input_has_ended)
   if (limit-buffer==change_limit-change_buffer)
    if (buffer[0]==change_buffer[0])
      if (change_limit>change_buffer) check_change();
}

@ @<Read from |change_file|...@>= {
  change_line++;
  if (!input_ln(change_file)) {
    err_print("! Change file ended without @@z");
@.Change file ended...@>
    buffer[0]='@@'; buffer[1]='z'; limit=buffer+2;
  }
  if (limit>buffer) { /* check if the change has ended */
    if (change_pending) {
      if_section_start_make_pending(0);
      if (change_pending) {
        changed_section[section_count]=1; change_pending=0;
      }
    }
    *limit=' ';
    if (buffer[0]=='@@') {
      if (xisupper(buffer[1])) buffer[1]=tolower(buffer[1]);
      if (buffer[1]=='x' || buffer[1]=='y') {
        loc=buffer+2;
        err_print("! Where is the matching @@z?");
@.Where is the match...@>
      }
      else if (buffer[1]=='z') {
        prime_the_change_buffer(); changing=!changing; print_where=1;
      }
    }
  }
}

@ At the end of the program, we will tell the user if the change file
had a line that didn't match any relevant line in |web_file|.

@c
void
check_complete(){
  if (change_limit!=change_buffer) { /* |changing| is 0 */
    strncpy(buffer,change_buffer,change_limit-change_buffer+1);
    limit=buffer+(int)(change_limit-change_buffer);
    changing=1; change_depth=include_depth; loc=buffer;
    err_print("! Change file entry did not match");
@.Change file entry did not match@>
  }
}

@** Storage of names and strings.
Both \.{CWEAVE} and \.{CTANGLE} store identifiers, section names and
other strings in a large array of |char|s, called |byte_mem|.
Information about the names is kept in the array |name_dir|, whose
elements are structures of type |name_info|, containing a pointer into
the |byte_mem| array (the address where the name begins) and other data.
A |name_pointer| variable is a pointer into |name_dir|.

@d max_bytes 90000 /* the number of bytes in identifiers,
  index entries, and section names; must be less than $2^{24}$ */
@d max_names 4000 /* number of identifiers, strings, section names;
  must be less than 10240 */

@<Definitions that...@>=
typedef struct name_info {
  char *byte_start; /* beginning of the name in |byte_mem| */
  @<More elements of |name_info| structure@>@;
} name_info; /* contains information about an identifier or section name */
typedef name_info *name_pointer; /* pointer into array of |name_info|s */
char byte_mem[max_bytes]; /* characters of names */
char *byte_mem_end = byte_mem+max_bytes-1; /* end of |byte_mem| */
name_info name_dir[max_names]; /* information about names */
name_pointer name_dir_end = name_dir+max_names-1; /* end of |name_dir| */

@ The actual sequence of characters in the name pointed to by a |name_pointer
p| appears in positions |p->byte_start| to |(p+1)->byte_start-1|, inclusive.
The |print_id| macro prints this text on the user's terminal.

@d length(c) (c+1)->byte_start-(c)->byte_start /* the length of a name */
@d print_id(c) term_write((c)->byte_start,length((c))) /* print identifier */

@ The first unused position in |byte_mem| and |name_dir| is
kept in |byte_ptr| and |name_ptr|, respectively.  Thus we
usually have |name_ptr->byte_start==byte_ptr|, and certainly
we want to keep |name_ptr<=name_dir_end| and |byte_ptr<=byte_mem_end|.

@<Defini...@>=
name_pointer name_ptr; /* first unused position in |byte_start| */
char *byte_ptr; /* first unused position in |byte_mem| */

@ @<Init...@>=
name_dir->byte_start=byte_ptr=byte_mem; /* position zero in both arrays */
name_ptr=name_dir+1; /* |name_dir[0]| will be used only for error recovery */
name_ptr->byte_start=byte_mem; /* this makes name 0 of length zero */

@ The names of identifiers are found by computing a hash address |h| and
then looking at strings of bytes signified by the |name_pointer|s
|hash[h]|, |hash[h]->link|, |hash[h]->link->link|, \dots,
until either finding the desired name or encountering the null pointer.

@<More elements of |name...@>=
struct name_info *link;

@ The hash table itself
consists of |hash_size| entries of type |name_pointer|, and is
updated by the |id_lookup| procedure, which finds a given identifier
and returns the appropriate |name_pointer|. The matching is done by the
function |names_match|, which is slightly different in
\.{CWEAVE} and \.{CTANGLE}.  If there is no match for the identifier,
it is inserted into the table.

@d hash_size 353 /* should be prime */

@<Defini...@>=
typedef name_pointer *hash_pointer;
name_pointer hash[hash_size]; /* heads of hash lists */
hash_pointer hash_end = hash+hash_size-1; /* end of |hash| */
hash_pointer h; /* index into hash-head array */

@ @<Predec...@>=
extern int names_match();

@ Initially all the hash lists are empty.

@<Init...@>=
for (h=hash; h<=hash_end; *h++=NULL) ;

@ Here is the main procedure for finding identifiers:

@c
name_pointer
id_lookup(first,last,t) /* looks up a string in the identifier table */
char *first; /* first character of string */
char *last; /* last character of string plus one */
char t; /* the |ilk|; used by \.{CWEAVE} only */
{
  char *i=first; /* position in |buffer| */
  int h; /* hash code */
  int l; /* length of the given identifier */
  name_pointer p; /* where the identifier is being sought */
  if (last==NULL) for (last=first; *last!='\0'; last++);
  l=last-first; /* compute the length */
  @<Compute the hash code |h|@>;
  @<Compute the name location |p|@>;
  if (p==name_ptr) @<Enter a new name into the table at position |p|@>;
  return(p);
}

@ A simple hash code is used: If the sequence of
character codes is $c_1c_2\ldots c_n$, its hash value will be
$$(2^{n-1}c_1+2^{n-2}c_2+\cdots+c_n)\,\bmod\,|hash_size|.$$

@<Compute the hash...@>=
h=(unsigned char)*i;
while (++i<last) h=(h+h+(int)((unsigned char)*i)) % hash_size;
@^high-bit character handling@>

@ If the identifier is new, it will be placed in position |p=name_ptr|,
otherwise |p| will point to its existing location.

@<Compute the name location...@>=
p=hash[h];
while (p && !names_match(p,first,l,t)) p=p->link;
if (p==NULL) {
  p=name_ptr; /* the current identifier is new */
  p->link=hash[h]; hash[h]=p; /* insert |p| at beginning of hash list */
}

@ The information associated with a new identifier must be initialized
in a slightly different way in \.{CWEAVE} than in \.{CTANGLE}; hence the
|init_p| procedure.

@<Pred...@>=
void init_p();

@ @<Enter a new name...@>= {
  if (byte_ptr+l>byte_mem_end) overflow("byte memory");
  if (name_ptr>=name_dir_end) overflow("name");
  strncpy(byte_ptr,first,l);
  (++name_ptr)->byte_start=byte_ptr+=l;
  if (program==cweave) init_p(p,t);
}

@ The names of sections are stored in |byte_mem| together