/* interp.c

    reentrant eval for som3j		22 Dec 2004
    som-in-som						30 Dec 2004
 */

// system area  1 .. MAXSYS-1
//   1..80   tokstring-som

#include "compile.h"
// #include "interp.h"

#define   TRUE	 	1
#define	  FALSE		0
#define	  NIL		0
#define   FUDGE     16   /* scratch area+3 check stkovf */

#define   TOS       SS[sp]
#define   NEXT      SS[sp-1]
#define   pop2		sp -= 2
#define	  pop1      sp--

#define   push(x)	sp++; SS[sp] = (x)
#define   pop(x)	(x) = SS[sp]; sp--

#define		PRIVATE 	static

int M[MAXMEM];	 		// memory
int *CS = &M[MAXDS];	// code segment
PRIVATE int SS[MAXSS];	// stack segment
PRIVATE	int sp=1,fp=0;	// current state SS

int CS_SOM = 0;			// start CS of SOM, init by load obj
int DP = MAXSYS;		// current free data segment

void error(char *mess, int ip){
    printf("%s at ip %d\n",mess,ip);
    exit(0);
}

// static alloc memory of size a
int xalloc(int a){
    int b;
    b = DP;
    if( DP + a >= MAXDS )
        error("xalloc: out of memory",0);
    DP += a;
    return b;
}

// gets() and put it in M[ads]
void dogets(int ads){
    char buf[256], *c;
    int i;
    c = gets(buf);
    if( c != NULL ){
        for(i=0; buf[i] != 0; i++, ads++)
            M[ads] = (int)buf[i] & 255;
        M[ads] = 0;
    }else{
        M[ads] = EOF_CHAR;
        M[ads+1] = 0;
    }
}

// reentrant eval
void eval(int ref){
    int runflag;
    int ip, op, data;	// current instruction
    int a, b, low, hi, var;

    ip = ref;
    runflag = 1;
    while(runflag ) {
        op = CS[ip] & 255;
        data = CS[ip] >> 8 ;

    switch(op){
    case icLit:
        push(data);
        ip++;
        break;
    case icLd:
        push( M[data]);
        ip++;
        break;
    case icSt:
        M[data] = TOS;
        pop1;
        ip++;
        break;
    case icPut:
        pop(a);
        SS[fp-data] = a;
        ip++;
        break;
    case icGet:
        push(SS[fp-data]);
        ip++;
        break;
    case icLdx:
        a = NEXT + TOS;
        pop1;
        TOS = M[a];
        ip++;
        break;
    case icStx:
        pop(a);
        b = NEXT + TOS;
        pop2;
        M[b] = a;
        ip++;
        break;
    case icArray:
        pop(a);
        push(xalloc(a));
        ip++;
        break;
    case icJmp:
        ip += data;
        break;
    case icJf:
        pop(a);
        if( a == FALSE) ip += data;
        else ip++;
        break;
    case icJt:
        pop(a);
        if( a != FALSE) ip += data;
        else ip++;
        break;
    case icCall:
        var = CS[data] >> 8;		// get lv
        if (sp + var + FUDGE > MAXSS)
            error("stack overflow",ip);
        SS[sp+var] = fp;
        fp = sp + var;
        sp = fp + 1;
        SS[sp] = ip + 1;
        ip = data + 1;
        break;
    case icRet:
    /* return TOS to caller if current stack is not empty */
        ip = SS[fp+1];
        if ( sp > fp+1 ){
            a = TOS;
            sp = fp - data + 1;
            fp = SS[fp];
            SS[sp] = a;
        }else{
            sp = fp - data;
            fp = SS[fp];
        }
        break;
    case icAdd:
        a = NEXT + TOS;
        pop1;
        TOS = a;
        ip++;
        break;
    case icSub:
        a = NEXT - TOS;
        pop1;
        TOS = a;
        ip++;
        break;
    case icMul:
        a = NEXT * TOS;
        pop1;
        TOS = a;
        ip++;
        break;
    case icDiv:
        a = NEXT / TOS;
        pop1;
        TOS = a;
        ip++;
        break;
    case icBand:
        a = NEXT & TOS;
        pop1;
        TOS = a;
        ip++;
        break;
    case icBor:
        a = NEXT | TOS;
        pop1;
        TOS = a;
        ip++;
        break;
    case icBxor:
        a = NEXT ^ TOS;
        pop1;
        TOS = a;
        ip++;
        break;
    case icNot:
        a = TOS == FALSE;
        TOS = a;
        ip++;
        break;
    case icMod:
        a = NEXT % TOS;
        pop1;
        TOS = a;
        ip++;
        break;
    case icShl:
        a = NEXT << TOS;
        pop1;
        TOS = a;
        ip++;
        break;
    case icShr:
        a = NEXT >> TOS;
        pop1;
        TOS = a;
        ip++;
        break;
    case icEq:
        a = NEXT == TOS;
        pop1;
        TOS = a;
        ip++;
        break;
    case icNe:
        a = NEXT != TOS;
        pop1;
        TOS = a;
        ip++;
        break;
    case icLt:
        a = NEXT < TOS;
        pop1;
        TOS = a;
        ip++;
        break;
    case icLe:
        a = NEXT <= TOS;
        pop1;
        TOS = a;
        ip++;
        break;
    case icGt:
        a = NEXT > TOS;
        pop1;
        TOS = a;
        ip++;
        break;
    case icGe:
        a = NEXT >= TOS;
        pop1;
        TOS = a;
        ip++;
        break;
    case icInc:
        SS[fp-data]++;
        ip++;
        break;
    case icDec:
        SS[fp-data]--;
        ip++;
        break;
    case icCase:
        low = CS[ip+1] >> 8;
        hi = CS[ip+2] >> 8;
        pop(a);
        if( a < low || a > hi )
            ip = ip+3;
        else
            ip += a-low+4;
        break;
    case icSys:
        switch(data){
        case 1: 			// print int
            pop(a);
            printf("%d",a);
            break;
        case 2: 			// print char
            pop(a);
            printf("%c",a);
            break;
        case 3: 			// get char
            push(getchar());
            break;
        case 4:			   // gets()
            pop(a);		   // som buffer
            dogets(a);
            break;
        case 5:				// eval ref
            pop(a);
            CS = &M[CS_SOM]; // switch to user space
            eval(a);
            CS = &M[MAXDS];	// switch back
            break;

        case 7:
            runflag = 0;	 	// end
            break;

        default: error("undefined syscall",ip);
        }
        ip++;
        break;

    case icEnd:
        runflag = 0;
        break;
    default:
    printf("op %d\n",op);
        error("undefined opcode",ip);
    }
    // end swich(op)

    } // end while runflag
}