execute.c


/********************************************
execute.c
copyright 1991-1996,2014-2016 Michael D. Brennan

This is a source file for mawk, an implementation of
the AWK programming language.

Mawk is distributed without warranty under the terms of
the GNU General Public License, version 3, 2007.

If you import elements of this code into another product,
you agree to not name that product mawk.
********************************************/

#include "mawk.h"
#include "code.h"
#include "types_string.h"
#include "table.h"
#include "types_int.h"
#include "field.h"
#include "bi_funct.h"
#include "bi_vars.h"
#include "regexp.h"
#include "repl.h"
#include "fin.h"
#include <math.h>

static int compare( CELL * );
static int d_to_index( double );

#ifdef NOINFO_SIGFPE
static char dz_msg[] = "division by zero";
#define CHECK_DIVZERO( x )  \
    if ( ( x ) == 0.0 )     \
        rt_error( dz_msg ); \
    else
#endif

#ifdef DEBUG
static void eval_overflow( void );

#define inc_sp()                                \
    if ( ++sp == eval_stack + EVAL_STACK_SIZE ) \
    eval_overflow()
#else

/* If things are working, the eval stack should not overflow */

#define inc_sp() sp++
#endif

#define SAFETY 16
#define DANGER ( EVAL_STACK_SIZE - SAFETY )

/*  The stack machine that executes the code */

CELL eval_stack[EVAL_STACK_SIZE];
/* these can move for deep recursion */
static CELL * stack_base   = eval_stack;
static CELL * stack_danger = eval_stack + DANGER;

#ifdef DEBUG
static void
eval_overflow( void )
{
    overflow( "eval stack", EVAL_STACK_SIZE );
}
#endif

/* clean up aloop stack on next, return, exit */
#define CLEAR_ALOOP_STACK()                   \
    do {                                      \
        if ( aloop_stack ) {                  \
            clear_aloop_stack( aloop_stack ); \
            aloop_stack = 0;                  \
        }                                     \
    } while ( 0 )

static void
clear_aloop_stack( ALoop * top )
{
    do {
        ALoop * hold = top;
        top          = top->link;
        aloop_free( hold );
    } while ( top );
}

static INST * restart_label; /* control flow labels */
INST *        next_label;
static CELL   tc;     /*useful temp */
static CELL   unused; /*unuseful rarely used temp */

int
_mawk_execute(
    INST *          cdp, /* code ptr, start execution here */
    register CELL * sp,  /* eval_stack pointer */
    CELL *          fp   /* frame ptr into eval_stack for user defined funcs */
)
{
    /* some useful temporaries */
    CELL * cp;
    int    t;

    /* stacks array loops for nesting */
    ALoop * aloop_stack = 0;

    /* for moving the eval stack on deep recursion */
    CELL * old_stack_base = 0;
    CELL * old_sp         = 0;

#ifdef DEBUG
    CELL * entry_sp = sp;
#endif

    if ( fp ) {
        /* we are a function call, check for deep recursion */
        if ( sp > stack_danger ) { /* change stacks */
            old_stack_base = stack_base;
            old_sp         = sp;
            stack_base     = (CELL *)zmalloc( sizeof( CELL ) * EVAL_STACK_SIZE );
            stack_danger   = stack_base + DANGER;
            sp             = stack_base;
            /* waste 1 slot for ANSI, actually large model msdos breaks in
	     RET if we don't */
#ifdef DEBUG
            entry_sp = sp;
#endif
        }
        else
            old_stack_base = (CELL *)0;
    }

    while ( 1 )
        switch ( cdp++->op ) {

                /* HALT only used by the disassemble now ; this remains
   so compilers don't offset the jump table */
            case _HALT:

            case _STOP: /* only for range patterns */
#ifdef DEBUG
                if ( sp != entry_sp + 1 )
                    bozo( "stop0" );
#endif
                return 1;

            case _PUSHC:
                inc_sp();
                cellcpy( sp, (CELL *)( cdp++->ptr ) );
                break;

            case _PUSHD:
                inc_sp();
                sp->type = C_DOUBLE;
                sp->dval = *(double *)cdp++->ptr;
                break;

            case _PUSHS:
                inc_sp();
                sp->type = C_STRING;
                sp->ptr  = cdp++->ptr;
                string( sp )->ref_cnt++;
                break;

            case PUSHFM:
                inc_sp();
                sp->ptr = cdp++->ptr;
                break;

            case F_PUSHA:
                cp = (CELL *)cdp->ptr;
                if ( cp != field ) {
                    if ( nf < 0 )
                        split_field0();

                    if ( !(
#ifdef MSDOS
                             SAMESEG( cp, field ) &&
#endif
                             cp >= NF && cp <= LAST_PFIELD ) ) {
                        /* its a real field $1, $2 ...
		     If its greater than $NF, we have to
		     make sure its set to ""  so that
		     (++|--) and g?sub() work right
		  */
                        t = field_addr_to_index( cp );
                        if ( t > nf ) {
                            cell_destroy( cp );
                            cp->type = C_STRING;
                            cp->ptr  = (void *)&null_str;
                            null_str.ref_cnt++;
                        }
                    }
                }
                /* fall thru */

            case _PUSHA:
            case A_PUSHA:
                inc_sp();
                sp->ptr = cdp++->ptr;
                break;

            case _PUSHI:
                /* put contents of next address on stack*/
                inc_sp();
                cellcpy( sp, (CELL *)( cdp++->ptr ) );
                break;

            case L_PUSHI:
                /* put the contents of a local var on stack,
	       cdp->op holds the offset from the frame pointer */
                inc_sp();
                cellcpy( sp, fp + cdp++->op );
                break;

            case L_PUSHA:
                /* put a local address on eval stack */
                inc_sp();
                sp->ptr = (void *)( fp + cdp++->op );
                break;

            case F_PUSHI:

                /* push contents of $i
	       cdp[0] holds & $i , cdp[1] holds i */

                inc_sp();
                if ( nf < 0 )
                    split_field0();
                cp = (CELL *)cdp->ptr;
                t  = ( cdp + 1 )->op;
                cdp += 2;

                if ( t <= nf )
                    cellcpy( sp, cp );
                else /* an unset field */
                {
                    sp->type = C_STRING;
                    sp->ptr  = (void *)&null_str;
                    null_str.ref_cnt++;
                }
                break;

            case NF_PUSHI:

                inc_sp();
                if ( nf < 0 )
                    split_field0();
                cellcpy( sp, NF );
                break;

            case FE_PUSHA:

                if ( sp->type != C_DOUBLE )
                    cast1_to_d( sp );

                t = d_to_index( sp->dval );
                if ( t && nf < 0 )
                    split_field0();
                sp->ptr = (void *)field_ptr( t );
                if ( t > nf ) {
                    /* make sure its set to "" */
                    cp = (CELL *)sp->ptr;
                    cell_destroy( cp );
                    cp->type = C_STRING;
                    cp->ptr  = (void *)&null_str;
                    null_str.ref_cnt++;
                }
                break;

            case FE_PUSHI:

                if ( sp->type != C_DOUBLE )
                    cast1_to_d( sp );

                t = d_to_index( sp->dval );

                if ( nf < 0 )
                    split_field0();
                if ( t <= nf )
                    cellcpy( sp, field_ptr( t ) );
                else {
                    sp->type = C_STRING;
                    sp->ptr  = (void *)&null_str;
                    null_str.ref_cnt++;
                }
                break;

            case AE_PUSHA:
                /* top of stack has an expr, cdp->ptr points at an
	   array, replace the expr with the cell address inside
	   the array */

                cp = array_find( (ARRAY)cdp++->ptr, sp, CREATE );
                cell_destroy( sp );
                sp->ptr = (void *)cp;
                break;

            case AE_PUSHI:
                /* top of stack has an expr, cdp->ptr points at an
	   array, replace the expr with the contents of the
	   cell inside the array */

                cp = array_find( (ARRAY)cdp++->ptr, sp, CREATE );
                cell_destroy( sp );
                cellcpy( sp, cp );
                break;

            case LAE_PUSHI:
                /*	sp[0] is an expression
	    cdp->op is offset from frame pointer of a CELL which
	       has an ARRAY in the ptr field, replace expr
	    with  array[expr]
	*/
                cp = array_find( (ARRAY)fp[cdp++->op].ptr, sp, CREATE );
                cell_destroy( sp );
                cellcpy( sp, cp );
                break;

            case LAE_PUSHA:
                /*	sp[0] is an expression
	    cdp->op is offset from frame pointer of a CELL which
	       has an ARRAY in the ptr field, replace expr
	    with  & array[expr]
	*/
                cp = array_find( (ARRAY)fp[cdp++->op].ptr, sp, CREATE );
                cell_destroy( sp );
                sp->ptr = (void *)cp;
                break;

            case LA_PUSHA:
                /*	cdp->op is offset from frame pointer of a CELL which
	       has an ARRAY in the ptr field. Push this ARRAY
	       on the eval stack
	*/
                inc_sp();
                sp->ptr = fp[cdp++->op].ptr;
                break;

            case PI_LOAD: /* load parameter info used for length(A) */
                /* when coded type of A was unknown, patch it now */
                {
                    SYMTAB * stp = (SYMTAB *)cdp->ptr;
                    cdp--;
                    switch ( stp->type ) {
                        case ST_VAR:
                            cdp[0].op  = _PUSHI;
                            cdp[1].ptr = stp->stval.cp;
                            break;
                        case ST_ARRAY:
                            cdp[0].op  = A_PUSHA;
                            cdp[1].ptr = stp->stval.array;
                            /* cdp[2].op is _BUILTIN */
                            cdp[3].ptr = (void *)bi_alength;
                            break;
                        default: /* ST_NONE is possible but weird */
                            cdp[0].op  = _PUSHI;
                            cdp[1].ptr = &unused;
                            break;
                    }
                }
                /* code just patched will execute now */
                break;

            case LPI_LOAD: /* load local parameter info used for length(A) */
                /* when coded type of A was unknown, patch it now */
                {
                    Local_PI * pi     = (Local_PI *)cdp->ptr;
                    FBLOCK *   fbp    = pi->fbp;
                    unsigned   offset = pi->offset;
                    int        type   = fbp->typev[offset];

                    ZFREE( pi );
                    cdp--;
                    switch ( type ) {
                        case ST_LOCAL_VAR:
                            cdp[0].op = L_PUSHI;
                            cdp[1].op = offset;
                            break;
                        case ST_LOCAL_ARRAY:
                            cdp[0].op = LA_PUSHA;
                            cdp[1].op = offset;
                            /* cdp[2].op is _BUILTIN */
                            cdp[3].ptr = (void *)bi_alength;
                            break;
                        default: /* ST_LOCAL_NONE is possible but weird */
                            cdp[0].op  = _PUSHI;
                            cdp[1].ptr = &unused;
                            break;
                    }
                }
                /* code just patched will execute now */
                break;

            case SET_ALOOP: {
                /* for (i in A)
		   address of A is in sp[0]
		   address of i is in sp[-1]
		*/
                ALoop * al = make_aloop( (ARRAY)sp[0].ptr, (CELL *)sp[-1].ptr );
                sp -= 2;
                /* stack it for nesting */
                al->link    = aloop_stack;
                aloop_stack = al;
                cdp += cdp->op;
            } break;

            case ALOOP: {
                ALoop * al = aloop_stack;
                if ( aloop_next( al ) ) {
                    /* execute body of loop */
                    cdp += cdp->op;
                }
                else {
                    /* loop is done */
                    cdp++;
                }
            } break;

            case POP_AL: {
                /* finish up an array loop */
                ALoop * al  = aloop_stack;
                aloop_stack = al->link;
                aloop_free( al );
            } break;

            case _POP:
                cell_destroy( sp );
                sp--;
                break;

            case _ASSIGN:
                /* top of stack has an expr, next down is an
	       address, put the expression in *address and
	       replace the address with the expression */

                /* don't propagate type C_MBSTRN */
                if ( sp->type == C_MBSTRN )
                    check_strnum( sp );
                sp--;
                cell_destroy( ( (CELL *)sp->ptr ) );
                cellcpy( sp, cellcpy( (CELL *)sp->ptr, (CELL *)( sp + 1 ) ) );
                cell_destroy( sp + 1 );
                break;

            case F_ASSIGN:
                /* assign to a field  */
                if ( sp->type == C_MBSTRN )
                    check_strnum( sp );
                sp--;
                field_assign( (CELL *)sp->ptr, sp + 1 );
                cell_destroy( sp + 1 );
                cellcpy( sp, (CELL *)sp->ptr );
                break;

            case _ADD_ASG:
                if ( sp->type != C_DOUBLE )
                    cast1_to_d( sp );
                cp = (CELL *)( sp - 1 )->ptr;
                if ( cp->type != C_DOUBLE )
                    cast1_to_d( cp );

#if SW_FP_CHECK /* specific to V7 and XNX23A */
                clrerr();
#endif
                cp->dval += sp--->dval;
#if SW_FP_CHECK
                fpcheck();
#endif
                sp->type = C_DOUBLE;
                sp->dval = cp->dval;
                break;

            case _SUB_ASG:
                if ( sp->type != C_DOUBLE )
                    cast1_to_d( sp );
                cp = (CELL *)( sp - 1 )->ptr;
                if ( cp->type != C_DOUBLE )
                    cast1_to_d( cp );
#if SW_FP_CHECK
                clrerr();
#endif
                cp->dval -= sp--->dval;
#if SW_FP_CHECK
                fpcheck();
#endif
                sp->type = C_DOUBLE;
                sp->dval = cp->dval;
                break;

            case _MUL_ASG:
                if ( sp->type != C_DOUBLE )
                    cast1_to_d( sp );
                cp = (CELL *)( sp - 1 )->ptr;
                if ( cp->type != C_DOUBLE )
                    cast1_to_d( cp );
#if SW_FP_CHECK
                clrerr();
#endif
                cp->dval *= sp--->dval;
#if SW_FP_CHECK
                fpcheck();
#endif
                sp->type = C_DOUBLE;
                sp->dval = cp->dval;
                break;

            case _DIV_ASG:
                if ( sp->type != C_DOUBLE )
                    cast1_to_d( sp );
                cp = (CELL *)( sp - 1 )->ptr;
                if ( cp->type != C_DOUBLE )
                    cast1_to_d( cp );

#if NOINFO_SIGFPE
                CHECK_DIVZERO( sp->dval );
#endif

#if SW_FP_CHECK
                clrerr();
#endif
                cp->dval /= sp--->dval;
#if SW_FP_CHECK
                fpcheck();
#endif
                sp->type = C_DOUBLE;
                sp->dval = cp->dval;
                break;

            case _MOD_ASG:
                if ( sp->type != C_DOUBLE )
                    cast1_to_d( sp );
                cp = (CELL *)( sp - 1 )->ptr;
                if ( cp->type != C_DOUBLE )
                    cast1_to_d( cp );

#if NOINFO_SIGFPE
                CHECK_DIVZERO( sp->dval );
#endif

                cp->dval = fmod( cp->dval, sp--->dval );
                sp->type = C_DOUBLE;
                sp->dval = cp->dval;
                break;

            case _POW_ASG:
                if ( sp->type != C_DOUBLE )
                    cast1_to_d( sp );
                cp = (CELL *)( sp - 1 )->ptr;
                if ( cp->type != C_DOUBLE )
                    cast1_to_d( cp );
                cp->dval = pow( cp->dval, sp--->dval );
                sp->type = C_DOUBLE;
                sp->dval = cp->dval;
                break;

                /* will anyone ever use these ? */

            case F_ADD_ASG:
                if ( sp->type != C_DOUBLE )
                    cast1_to_d( sp );
                cp = (CELL *)( sp - 1 )->ptr;
                cast1_to_d( cellcpy( &tc, cp ) );
#if SW_FP_CHECK
                clrerr();
#endif
                tc.dval += sp--->dval;
#if SW_FP_CHECK
                fpcheck();
#endif
                sp->type = C_DOUBLE;
                sp->dval = tc.dval;
                field_assign( cp, &tc );
                break;

            case F_SUB_ASG:
                if ( sp->type != C_DOUBLE )
                    cast1_to_d( sp );
                cp = (CELL *)( sp - 1 )->ptr;
                cast1_to_d( cellcpy( &tc, cp ) );
#if SW_FP_CHECK
                clrerr();
#endif
                tc.dval -= sp--->dval;
#if SW_FP_CHECK
                fpcheck();
#endif
                sp->type = C_DOUBLE;
                sp->dval = tc.dval;
                field_assign( cp, &tc );
                break;

            case F_MUL_ASG:
                if ( sp->type != C_DOUBLE )
                    cast1_to_d( sp );
                cp = (CELL *)( sp - 1 )->ptr;
                cast1_to_d( cellcpy( &tc, cp ) );
#if SW_FP_CHECK
                clrerr();
#endif
                tc.dval *= sp--->dval;
#if SW_FP_CHECK
                fpcheck();
#endif
                sp->type = C_DOUBLE;
                sp->dval = tc.dval;
                field_assign( cp, &tc );
                break;

            case F_DIV_ASG:
                if ( sp->type != C_DOUBLE )
                    cast1_to_d( sp );
                cp = (CELL *)( sp - 1 )->ptr;
                cast1_to_d( cellcpy( &tc, cp ) );

#if NOINFO_SIGFPE
                CHECK_DIVZERO( sp->dval );
#endif

#if SW_FP_CHECK
                clrerr();
#endif
                tc.dval /= sp--->dval;
#if SW_FP_CHECK
                fpcheck();
#endif
                sp->type = C_DOUBLE;
                sp->dval = tc.dval;
                field_assign( cp, &tc );
                break;

            case F_MOD_ASG:
                if ( sp->type != C_DOUBLE )
                    cast1_to_d( sp );
                cp = (CELL *)( sp - 1 )->ptr;
                cast1_to_d( cellcpy( &tc, cp ) );

#if NOINFO_SIGFPE
                CHECK_DIVZERO( sp->dval );
#endif

                tc.dval  = fmod( tc.dval, sp--->dval );
                sp->type = C_DOUBLE;
                sp->dval = tc.dval;
                field_assign( cp, &tc );
                break;

            case F_POW_ASG:
                if ( sp->type != C_DOUBLE )
                    cast1_to_d( sp );
                cp = (CELL *)( sp - 1 )->ptr;
                cast1_to_d( cellcpy( &tc, cp ) );
                tc.dval  = pow( tc.dval, sp--->dval );
                sp->type = C_DOUBLE;
                sp->dval = tc.dval;
                field_assign( cp, &tc );
                break;

            case _ADD:
                sp--;
                if ( CELL_PAIR_TYPE( sp ) != TWO_DOUBLES )
                    cast2_to_d( sp );
#if SW_FP_CHECK
                clrerr();
#endif
                sp[0].dval += sp[1].dval;
#if SW_FP_CHECK
                fpcheck();
#endif
                break;

            case _SUB:
                sp--;
                if ( CELL_PAIR_TYPE( sp ) != TWO_DOUBLES )
                    cast2_to_d( sp );
#if SW_FP_CHECK
                clrerr();
#endif
                sp[0].dval -= sp[1].dval;
#if SW_FP_CHECK
                fpcheck();
#endif
                break;

            case _MUL:
                sp--;
                if ( CELL_PAIR_TYPE( sp ) != TWO_DOUBLES )
                    cast2_to_d( sp );
#if SW_FP_CHECK
                clrerr();
#endif
                sp[0].dval *= sp[1].dval;
#if SW_FP_CHECK
                fpcheck();
#endif
                break;

            case _DIV:
                sp--;
                if ( CELL_PAIR_TYPE( sp ) != TWO_DOUBLES )
                    cast2_to_d( sp );

#if NOINFO_SIGFPE
                CHECK_DIVZERO( sp[1].dval );
#endif

#if SW_FP_CHECK
                clrerr();
#endif
                sp[0].dval /= sp[1].dval;
#if SW_FP_CHECK
                fpcheck();
#endif
                break;

            case _MOD:
                sp--;
                if ( CELL_PAIR_TYPE( sp ) != TWO_DOUBLES )
                    cast2_to_d( sp );

#if NOINFO_SIGFPE
                CHECK_DIVZERO( sp[1].dval );
#endif

                sp[0].dval = fmod( sp[0].dval, sp[1].dval );
                break;

            case _POW:
                sp--;
                if ( CELL_PAIR_TYPE( sp ) != TWO_DOUBLES )
                    cast2_to_d( sp );
                sp[0].dval = pow( sp[0].dval, sp[1].dval );
                break;

            case _NOT:
                /* evaluates to 0.0 or 1.0 */
            reswitch_1:
                switch ( sp->type ) {
                    case C_NOINIT:
                        sp->dval = 1.0;
                        break;
                    case C_DOUBLE:
                        sp->dval = sp->dval != 0.0 ? 0.0 : 1.0;
                        break;
                    case C_STRING:
                        sp->dval = string( sp )->len ? 0.0 : 1.0;
                        free_STRING( string( sp ) );
                        break;
                    case C_STRNUM: /* test as a number */
                        sp->dval = sp->dval != 0.0 ? 0.0 : 1.0;
                        free_STRING( string( sp ) );
                        break;
                    case C_MBSTRN:
                        check_strnum( sp );
                        goto reswitch_1;
                    default:
                        bozo( "bad type on eval stack" );
                }
                sp->type = C_DOUBLE;
                break;

            case _TEST:
                /* evaluates to 0.0 or 1.0 */
            reswitch_2:
                switch ( sp->type ) {
                    case C_NOINIT:
                        sp->dval = 0.0;
                        break;
                    case C_DOUBLE:
                        sp->dval = sp->dval != 0.0 ? 1.0 : 0.0;
                        break;
                    case C_STRING:
                        sp->dval = string( sp )->len ? 1.0 : 0.0;
                        free_STRING( string( sp ) );
                        break;
                    case C_STRNUM: /* test as a number */
                        sp->dval = sp->dval != 0.0 ? 1.0 : 0.0;
                        free_STRING( string( sp ) );
                        break;
                    case C_MBSTRN:
                        check_strnum( sp );
                        goto reswitch_2;
                    default:
                        bozo( "bad type on eval stack" );
                }
                sp->type = C_DOUBLE;
                break;

            case _UMINUS:
                if ( sp->type != C_DOUBLE )
                    cast1_to_d( sp );
                sp->dval = -sp->dval;
                break;

            case _UPLUS:
                if ( sp->type != C_DOUBLE )
                    cast1_to_d( sp );
                break;

            case _CAT: {
                unsigned len1, len2;
                char *   str1, *str2;
                STRING * b;

                sp--;
                if ( CELL_PAIR_TYPE( sp ) != TWO_STRINGS )
                    cast2_to_s( sp );
                str1 = string( sp )->str;
                len1 = string( sp )->len;
                str2 = string( sp + 1 )->str;
                len2 = string( sp + 1 )->len;

                b = new_STRING0( len1 + len2 );
                memcpy( b->str, str1, len1 );
                memcpy( b->str + len1, str2, len2 );
                free_STRING( string( sp ) );
                free_STRING( string( sp + 1 ) );

                sp->ptr = (void *)b;
                break;
            }

            case _PUSHINT:
                inc_sp();
                sp->type = cdp++->op;
                break;

            case _BUILTIN:
            case _PRINT:
                sp = ( *(PF_CP)cdp++->ptr )( sp );
                break;

            case _POST_INC:
                cp = (CELL *)sp->ptr;
                if ( cp->type != C_DOUBLE )
                    cast1_to_d( cp );
                sp->type = C_DOUBLE;
                sp->dval = cp->dval;
                cp->dval += 1.0;
                break;

            case _POST_DEC:
                cp = (CELL *)sp->ptr;
                if ( cp->type != C_DOUBLE )
                    cast1_to_d( cp );
                sp->type = C_DOUBLE;
                sp->dval = cp->dval;
                cp->dval -= 1.0;
                break;

            case _PRE_INC:
                cp = (CELL *)sp->ptr;
                if ( cp->type != C_DOUBLE )
                    cast1_to_d( cp );
                sp->dval = cp->dval += 1.0;
                sp->type = C_DOUBLE;
                break;

            case _PRE_DEC:
                cp = (CELL *)sp->ptr;
                if ( cp->type != C_DOUBLE )
                    cast1_to_d( cp );
                sp->dval = cp->dval -= 1.0;
                sp->type = C_DOUBLE;
                break;

            case F_POST_INC:
                cp = (CELL *)sp->ptr;
                cellcpy( &tc, cp );
                cast1_to_d( &tc );
                sp->type = C_DOUBLE;
                sp->dval = tc.dval;
                tc.dval += 1.0;
                field_assign( cp, &tc );
                break;

            case F_POST_DEC:
                cp = (CELL *)sp->ptr;
                cellcpy( &tc, cp );
                cast1_to_d( &tc );
                sp->type = C_DOUBLE;
                sp->dval = tc.dval;
                tc.dval -= 1.0;
                field_assign( cp, &tc );
                break;

            case F_PRE_INC:
                cp = (CELL *)sp->ptr;
                cast1_to_d( cellcpy( sp, cp ) );
                sp->dval += 1.0;
                field_assign( cp, sp );
                break;

            case F_PRE_DEC:
                cp = (CELL *)sp->ptr;
                cast1_to_d( cellcpy( sp, cp ) );
                sp->dval -= 1.0;
                field_assign( cp, sp );
                break;

            case _JMP:
                cdp += cdp->op;
                break;

            case _JNZ:
                /* jmp if top of stack is non-zero and pop stack */
                if ( test( sp ) )
                    cdp += cdp->op;
                else
                    cdp++;
                cell_destroy( sp );
                sp--;
                break;

            case _JZ:
                /* jmp if top of stack is zero and pop stack */
                if ( !test( sp ) )
                    cdp += cdp->op;
                else
                    cdp++;
                cell_destroy( sp );
                sp--;
                break;

            case _LJZ:
                /* special jump for logical and */
                /* this is always preceded by _TEST */
                if ( sp->dval == 0.0 ) {
                    /* take jump, but don't pop stack */
                    cdp += cdp->op;
                }
                else {
                    /* pop and don't jump */
                    sp--;
                    cdp++;
                }
                break;

            case _LJNZ:
                /* special jump for logical or */
                /* this is always preceded by _TEST */
                if ( sp->dval != 0.0 ) {
                    /* take jump, but don't pop stack */
                    cdp += cdp->op;
                }
                else {
                    /* pop and don't jump */
                    sp--;
                    cdp++;
                }
                break;

                /*	the relation operations */
                /*	compare() makes sure string ref counts are OK */
            case _EQ:
                t        = compare( --sp );
                sp->type = C_DOUBLE;
                sp->dval = t == 0 ? 1.0 : 0.0;
                break;

            case _NEQ:
                t        = compare( --sp );
                sp->type = C_DOUBLE;
                sp->dval = t ? 1.0 : 0.0;
                break;

            case _LT:
                t        = compare( --sp );
                sp->type = C_DOUBLE;
                sp->dval = t < 0 ? 1.0 : 0.0;
                break;

            case _LTE:
                t        = compare( --sp );
                sp->type = C_DOUBLE;
                sp->dval = t <= 0 ? 1.0 : 0.0;
                break;

            case _GT:
                t        = compare( --sp );
                sp->type = C_DOUBLE;
                sp->dval = t > 0 ? 1.0 : 0.0;
                break;

            case _GTE:
                t        = compare( --sp );
                sp->type = C_DOUBLE;
                sp->dval = t >= 0 ? 1.0 : 0.0;
                break;

            case _MATCH0:
                /* does $0 match, the RE at cdp? */

                inc_sp();
                if ( field->type >= C_STRING ) {
                    sp->type = C_DOUBLE;
                    sp->dval = REtest( string( field )->str, string( field )->len, cdp++->ptr )
                                   ? 1.0
                                   : 0.0;

                    break /* the case */;
                }
                else {
                    cellcpy( sp, field );
                    /* and FALL THRU */
                }

            case _MATCH1:
                /* does expr at sp[0] match RE at cdp */
                if ( sp->type < C_STRING )
                    cast1_to_s( sp );
                t = REtest( string( sp )->str, string( sp )->len, cdp++->ptr );
                free_STRING( string( sp ) );
                sp->type = C_DOUBLE;
                sp->dval = t ? 1.0 : 0.0;
                break;

            case _MATCH2:
                /* does sp[-1] match sp[0] as re */
                cast_to_RE( sp );

                if ( ( --sp )->type < C_STRING )
                    cast1_to_s( sp );
                t = REtest( string( sp )->str, string( sp )->len, ( sp + 1 )->ptr );

                free_STRING( string( sp ) );
                sp->type = C_DOUBLE;
                sp->dval = t ? 1.0 : 0.0;
                break;

            case A_TEST:
                /* entry :	sp[0].ptr-> an array
		    sp[-1]  is an expression

	   we compute	(expression in array)  */
                sp--;
                cp = array_find( ( ARRAY )( ( sp + 1 )->ptr ), sp, NO_CREATE );
                cell_destroy( sp );
                sp->type = C_DOUBLE;
                sp->dval = ( cp != (CELL *)0 ) ? 1.0 : 0.0;
                break;

            case A_DEL:
                /* sp[0].ptr ->  array
	   sp[-1] is an expr
	   delete  array[expr]	*/

                array_delete( ( ARRAY )( sp->ptr ), (CELL *)( sp - 1 ) );
                cell_destroy( sp - 1 );
                sp -= 2;
                break;

            case DEL_A:
                /* free all the array at once */
                array_clear( ( ARRAY )( sp->ptr ) );
                sp--;
                break;

                /* form a multiple array index */
            case A_CAT:
                sp = array_cat( sp, cdp++->op );
                break;

            case _EXIT:
                if ( sp->type != C_DOUBLE )
                    cast1_to_d( sp );
                exit_code = d_to_int( sp->dval );
                sp--;
                /* fall thru */

            case _EXIT0:

                if ( !end_start )
                    mawk_exit( exit_code );

                cdp       = end_start;
                end_start = (INST *)0; /* makes sure next exit exits */

                if ( begin_start )
                    zfree( begin_start, begin_size );
                if ( main_start )
                    zfree( main_start, main_size );
                sp = eval_stack - 1; /* might be in user function */
                CLEAR_ALOOP_STACK(); /* ditto */
                break;

            case _JMAIN: /* go from BEGIN code to MAIN code */
                zfree( begin_start, begin_size );
                begin_start = (INST *)0;
                cdp         = main_start;
                break;

            case _OMAIN:
                if ( !main_fin )
                    open_main();
                restart_label = cdp;
                cdp           = next_label;
                break;

            case _NEXT:
                /* next might be inside an aloop -- clear stack */
                CLEAR_ALOOP_STACK();
                cdp = next_label;
                break;

            case _NEXTFILE:
                /* nextfile might be inside an aloop -- clear stack */
                CLEAR_ALOOP_STACK();
                next_main( 0 );
                cdp = next_label;
                break;

            case OL_GL: {
                char * p;
                size_t len;

                if ( !( p = FINgets( main_fin, &len ) ) ) {
                    if ( !end_start )
                        mawk_exit( 0 );

                    cdp = end_start;
                    zfree( main_start, main_size );
                    main_start = end_start = (INST *)0;
                }
                else {
                    set_field0( p, len );
                    cdp = restart_label;
                    rt_nr++;
                    rt_fnr++;
                }
            } break;

            /* two kinds of OL_GL is a historical stupidity from working on
	    a machine with very slow floating point emulation */
            case OL_GL_NR: {
                char * p;
                size_t len;

                if ( !( p = FINgets( main_fin, &len ) ) ) {
                    if ( !end_start )
                        mawk_exit( 0 );

                    cdp = end_start;
                    zfree( main_start, main_size );
                    main_start = end_start = (INST *)0;
                }
                else {
                    set_field0( p, len );
                    cdp = restart_label;

                    if ( CELL_PAIR_TYPE( NR ) != TWO_DOUBLES )
                        cast2_to_d( NR );

                    NR->dval += 1.0;
                    rt_nr++;
                    FNR->dval += 1.0;
                    rt_fnr++;
                }
            } break;

            case _RANGE:
                /* test a range pattern:  pat1, pat2 { action }
   entry :
       cdp[0].op -- a flag, test pat1 if on else pat2
       cdp[1].op -- offset of pat2 code from cdp
       cdp[2].op -- offset of action code from cdp
       cdp[3].op -- offset of code after the action from cdp
       cdp[4] -- start of pat1 code
*/

#define FLAG cdp[0].op
#define PAT2 cdp[1].op
#define ACTION cdp[2].op
#define FOLLOW cdp[3].op
#define PAT1 4

                if ( FLAG ) /* test again pat1 */
                {
                    _mawk_execute( cdp + PAT1, sp, fp );
                    t = test( sp + 1 );
                    cell_destroy( sp + 1 );
                    if ( t )
                        FLAG = 0;
                    else {
                        cdp += FOLLOW;
                        break; /* break the switch */
                    }
                }

                /* test against pat2 and then perform the action */
                _mawk_execute( cdp + PAT2, sp, fp );
                FLAG = test( sp + 1 );
                cell_destroy( sp + 1 );
                cdp += ACTION;
                break;

                /* function calls  */

            case _RET0:
                inc_sp();
                sp->type = C_NOINIT;
                /* fall thru */

            case _RET:

#ifdef DEBUG
                if ( sp != entry_sp + 1 )
                    bozo( "ret" );
#endif
                if ( old_stack_base ) /* reset stack */
                {
                    /* move the return value */
                    cellcpy( old_sp + 1, sp );
                    cell_destroy( sp );
                    zfree( stack_base, sizeof( CELL ) * EVAL_STACK_SIZE );
                    stack_base   = old_stack_base;
                    stack_danger = old_stack_base + DANGER;
                }

                /* return might be inside an aloop -- clear stack */
                CLEAR_ALOOP_STACK();

                return 1;

            case _CALL:

                /*  cdp[0] holds ptr to "function block"
		cdp[1] holds number of input arguments
	    */

                {
                    FBLOCK * fbp     = (FBLOCK *)cdp++->ptr;
                    int      a_args  = cdp++->op;       /* actual number of args */
                    CELL *   nfp     = sp - a_args + 1; /* new fp for callee */
                    CELL *   local_p = sp + 1;          /* first local argument on stack */
                    char *   type_p  = 0;               /* pts to type of an argument */

                    if ( fbp->nargs )
                        type_p = fbp->typev + a_args - 1;

                    /* create space for locals */
                    t = fbp->nargs - a_args; /* t is number of locals */
                    while ( t > 0 ) {
                        t--;
                        sp++;
                        type_p++;
                        sp->type = C_NOINIT;
                        if ( *type_p == ST_LOCAL_ARRAY )
                            sp->ptr = (void *)new_ARRAY();
                    }

                    _mawk_execute( fbp->code, sp, nfp );

                    /* cleanup the callee's arguments */
                    /* putting return value at top of eval stack */
                    if ( sp >= nfp ) {
                        cp = sp + 1; /* cp -> the function return */

                        do {
                            if ( *type_p == ST_LOCAL_ARRAY ) {
                                if ( sp >= local_p ) {
                                    array_clear( ( ARRAY )( sp->ptr ) );
                                    ZFREE( (ARRAY)sp->ptr );
                                }
                            }
                            else
                                cell_destroy( sp );

                            type_p--;
                            sp--;

                        } while ( sp >= nfp );

                        cellcpy( ++sp, cp );
                        cell_destroy( cp );
                    }
                    else
                        sp++; /* no arguments passed */
                }
                break;

            default:
                bozo( "bad opcode" );
        }

    return 1;
}

/*
  return 0 if a numeric is zero else return non-zero
  return 0 if a string is "" else return non-zero
*/
int
test( CELL * cp )
{
reswitch:

    switch ( cp->type ) {
        case C_NOINIT:
            return 0;
        case C_STRNUM: /* test as a number */
        case C_DOUBLE:
            return cp->dval != 0.0;
        case C_STRING:
            return string( cp )->len;
        case C_MBSTRN:
            check_strnum( cp );
            goto reswitch;
        default:
            bozo( "bad cell type in call to test" );
    }
    return 0; /*can't get here: shutup */
}

/* compare cells at cp and cp+1 and
   frees STRINGs at those cells
*/
static int
compare( CELL * cp )
{
    int k;

reswitch:

    switch ( CELL_PAIR_TYPE( cp ) ) {
        case TWO_NOINITS:
            return 0;

        case TWO_DOUBLES:
        two_d:
            return cp->dval > ( cp + 1 )->dval ? 1 : cp->dval < ( cp + 1 )->dval ? -1 : 0;

        case TWO_STRINGS:
        case STRING_AND_STRNUM:
        two_s:
            k = STRING_cmp( string( cp ), string( cp + 1 ) );
            free_STRING( string( cp ) );
            free_STRING( string( cp + 1 ) );
            return k;

        case NOINIT_AND_DOUBLE:
        case NOINIT_AND_STRNUM:
        case DOUBLE_AND_STRNUM:
        case TWO_STRNUMS:
            cast2_to_d( cp );
            goto two_d;
        case NOINIT_AND_STRING:
        case DOUBLE_AND_STRING:
            cast2_to_s( cp );
            goto two_s;
        case TWO_MBSTRNS:
            check_strnum( cp );
            check_strnum( cp + 1 );
            goto reswitch;

        case NOINIT_AND_MBSTRN:
        case DOUBLE_AND_MBSTRN:
        case STRING_AND_MBSTRN:
        case STRNUM_AND_MBSTRN:
            check_strnum( cp->type == C_MBSTRN ? cp : cp + 1 );
            goto reswitch;

        default: /* there are no default cases */
            bozo( "bad cell type passed to compare" );
    }
    return 0; /* shut up */
}

/* does not assume target was a cell, if so
   then caller should have made a previous
   call to cell_destroy	 */

CELL *
cellcpy( CELL * target, CELL * source )
{
    switch ( target->type = source->type ) {
        case C_NOINIT:
        case C_SPACE:
        case C_SNULL:
            break;

        case C_DOUBLE:
            target->dval = source->dval;
            break;

        case C_STRNUM:
            target->dval = source->dval;
            /* fall thru */

        case C_REPL:
        case C_MBSTRN:
        case C_STRING:
            string( source )->ref_cnt++;
            /* fall thru */

        case C_RE:
        case C_REPLV:
            target->ptr = source->ptr;
            break;
        default:
            bozo( "bad cell passed to cellcpy()" );
            break;
    }
    return target;
}

#ifdef DEBUG

void
DB_cell_destroy( CELL * cp )
{
    switch ( cp->type ) {
        case C_NOINIT:
        case C_DOUBLE:
            break;

        case C_MBSTRN:
        case C_STRING:
        case C_STRNUM:
            free_STRING( string( cp ) );
            break;

        case C_RE:
            bozo( "cell destroy called on RE cell" );
        default:
            bozo( "cell destroy called on bad cell type" );
    }
}

#endif

/* convert a double d to a field index	$d -> $i */
static int
d_to_index( double d )
{

    if ( d >= 0.0 ) {
        return d_to_int( d );
    }
    /* might include nan */
    rt_error( "negative field index $%.6g", d );
    return 0; /* shutup */
}