//
// Pocket C ETA for the Palm Pilot
// (c) 2001 S.Sykes
// 
// 28 Mar 2001   v1.0  SDS  First working version
//  1 Apr 2001   v1.1  SDS  Massive optimisations.  This cross compiler has no optimisation in it,
//                          so doing stuff like x=a[y=z] really is quicker than x=a[z];y=z.
//  1 Apr 2001   v1.2  SDS  Changed to array based program storage - note maxlines
//  3 Apr 2001   v1.3  SDS  Fixed halibut bug, moved to dynamic memory for nums and nflags, 
//                          added div by 0 check & prog length check.  Tidied.
//  5 Apr 2001   v1.4  SDS  Fixed transfer out of range check.  Minor optimisation of halibut.
//

//
// Constants
//
#define VERSION "1.4"
#define MAXSTACK 100
#define MAXSTACKINDEX 99
#define MAXLINES 256
#define PROGNAME "ETA"
// #define DEBUG
// #define PROFILE

//
// Meta data
//
@cid "SSyk";
@name "ETA";
@dbname "ETA";
@ver VERSION;
@licon1 "eta-large.bmp";
@sicon1 "eta-small.bmp";

//
// Globals
//
int currentline=0;
#ifdef PROFILE
int tik;
#endif

//
// Error handling
//
barf(string s) {
#ifdef PROFILE
  puts("\nTicks taken = "+(ticks()-tik));
#endif
  if (currentline) alert(s+" at line "+(currentline-1));
  else alert(s);
  event(1);
  exit();
}

//
// Stack functions
// Note I've implemented these as inlines using #defs for performance
// Also note ppush and ppop - for using a single push and pop on the same line
//

int stack[MAXSTACK];
int stacktop=-1;

#define popcheck if (stacktop<0) barf("Stack underflow")
#define popchecktwo if (stacktop<=0) barf("Stack underflow")
#define pop stack[stacktop--]
#define ppop stack[stacktop]

#define pushcheck if (stacktop==MAXSTACKINDEX) barf("Stack overflow")
#define push stack[++stacktop]=
#define ppush stack[stacktop]=

halibut(int n) {
  int i,m,smn;
  if (n>0) {
    if (n>stacktop) barf("Stack underflow - positive halibut");
    m=stack[i=stacktop-n];
    while (i<stacktop) stack[i]=stack[++i];
    stack[i]=m;
  } else {
    if (-n>stacktop) barf("Stack underflow - negative halibut");
    stack[stacktop+1]=stack[n+stacktop++];
  }
}

//
// ETA program storage and read function
//
int readlines=1;
string theprog[MAXLINES];
int linelens[MAXLINES];

readprogram() {
  if (!mmfind(PROGNAME)) barf("Program not found - your program must be in a memo titled ETA");
  mmgetl();  // dispose of the title line
  while(!mmeof()) {
    linelens[readlines]=strlen(theprog[readlines]=strupr(mmgetl()));
    if (++readlines==MAXLINES) barf("Program too long, max lines="+MAXLINES);
  }
  mmclose();
}

//
// main program - read program from memo then interpret it
//

main() {
  int clinepos,accum,numberstate=1,cl,s1,s2,a;
  char ch;
  string cline;
  pointer nums,nflags;
  
  if (!(nflags=malloc(a=276))) barf("Yikes, malloc failed");  // this section is efficient but ugly
  while (a--) nflags[a]=0;           // may be quicker to unroll this a bit, but it's run once only
  nflags['E']=nflags['T']=nflags['A']=nflags['O']=nflags['I']=nflags['N']=nflags['S']=nflags['H']=1;
  nums=nflags+191;                   // ha, cunning re-use of space
  nums['T']=1;
  nums['A']=2;
  nums['O']=3;
  nums['I']=4;
  nums['N']=5;
  nums['S']=6;

#ifdef PROFILE
  tik=ticks();
#endif
  
  clear();
  puts("ETA interpreter for Palm OS v"+VERSION+"\n");
  readprogram();
  currentline=1;
  while(currentline<readlines) {  // line level loop
    cline=theprog[currentline];
    cl=linelens[currentline++];
    clinepos=0;
    while(cl--) {  // char level loop
      ch=cline@[clinepos++];
      if (nflags[ch]) if (numberstate) {  // it's just a two state state machine
        switch(ch) {
        case 'E': {
            popchecktwo;
            if (!(s1=pop)) barf("Divide by zero");
            ppush (s2=ppop)/s1;
            push s2%s1;
            break;
          }
        case 'T': {
            popchecktwo;
            a=pop;
#ifdef DEBUG
	        alert("T: Addr: "+a+" Cond: "+c);
#endif
            if (pop) {
              if (a<readlines && a>=0) currentline=a;
              else barf("Transfer out of range");
              if (!currentline) barf("Program terminated nicely (transfer to zero)");
              cl=0;
            }
            break;
          }
        case 'A': {
            pushcheck;
            push currentline;
            break;
          }
        case 'O': {
            popcheck;
            puts((char)pop);
            break;
          }
        case 'I': {
            pushcheck;
            puts((char)(push getc()));
            break;
          }
        case 'N': {
            numberstate=accum=0;
            break;
          }
        case 'S': {
            popchecktwo;
            s1=pop;
            ppush (ppop-s1);
            break;
          }
        case 'H': {
            popcheck;
            halibut(pop);
            break;
          }
        }
      } else { // in numberstate
        if (ch=='E') {
          pushcheck; 
          push accum; 
          numberstate=1;
        } else accum=accum*7+nums[ch];
      }
    }  // ends char level loop
  }
  barf("Program terminated normally");  // fell off the end of the program
}