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/*
** File: variable.c
**
** (C)opyright 1987-1992 InfoTaskforce.
*/
#include "infocom.h"
Void
get_var ( var )
word var ;
{
store ( load_var ( var ) ) ;
}
word
load_var ( var )
word var ;
{
extern byte_ptr global_ptr ;
extern word *stack_var_ptr ;
extern word *stack ;
register word value ;
register word *svp ;
register byte_ptr ptr ;
if ( var == 0 )
return ( *stack ) ;
else
{
if ( var < LOCAL_VARS )
{
/*
** In interpreters prior to VERSION_5, the "stack_var_ptr"
** pointed to the first local variable on the z_code stack.
** In VERSION_5 and subsequent interpreters, the "stack_var_ptr"
** points to the stack entry above the first local variable on
** the z_code stack.
**
** However, there is no reason for us not to adopt the VERSION_5
** method for all versions of the interpreter. This decision
** affects the following opcodes:
** gosub, std_rtn, load_var & put_var.
**
** Interpreters prior to VERSION_5 used the statement:
**
** svp = stack_var_ptr - ( var - 1 ) ;
**
** instead of:
**
** svp = stack_var_ptr - var ;
*/
svp = stack_var_ptr - var ;
return ( *svp ) ;
}
else
{
ptr = global_ptr + (( var - LOCAL_VARS ) << 1 ) ;
value = *(ptr++) << BITS_PER_BYTE ;
return ( (word)(value | *ptr) ) ;
}
}
}
Void
put_var ( var,value )
word var,value ;
{
extern byte_ptr global_ptr ;
extern word *stack_var_ptr ;
extern word *stack ;
register word *svp ;
register byte_ptr ptr ;
if ( var == 0 )
*stack = value ;
else
{
if ( var < LOCAL_VARS )
{
/*
** In interpreters prior to VERSION_5, the "stack_var_ptr"
** pointed to the first local variable on the z_code stack.
** In VERSION_5 and subsequent interpreters, the "stack_var_ptr"
** points to the stack entry above the first local variable on
** the z_code stack.
**
** However, there is no reason for us not to adopt the VERSION_5
** method for all versions of the interpreter. This decision
** affects the following opcodes:
** gosub, std_rtn, load_var & put_var.
**
** Interpreters prior to VERSION_5 used the statement:
**
** svp = stack_var_ptr - ( var - 1 ) ;
**
** instead of:
**
** svp = stack_var_ptr - var ;
*/
svp = stack_var_ptr - var ;
*svp = value ;
}
else
{
ptr = global_ptr + (( var - LOCAL_VARS ) << 1 ) ;
*ptr++ = MOST_SIGNIFICANT_BYTE ( value ) ;
*ptr = LEAST_SIGNIFICANT_BYTE ( value ) ;
}
}
}
Void
push ( value )
word value ;
{
extern word *stack ;
*(--stack) = value ;
}
Void
pop ( var )
word var ;
{
extern word *stack ;
put_var ( var,*stack++ ) ;
}
Void
inc_var ( var )
word var ;
{
put_var ( var,load_var ( var ) + 1 ) ;
}
Void
dec_var ( var )
word var ;
{
put_var ( var,load_var ( var ) - 1 ) ;
}
Void
inc_chk ( var,threshold )
word var,threshold ;
{
register word value ;
value = load_var ( var ) + 1 ;
put_var ( var,value ) ;
if ( (signed_word)value > (signed_word)threshold )
ret_value ( TRUE ) ;
else
ret_value ( FALSE ) ;
}
Void
dec_chk ( var,threshold )
word var,threshold ;
{
register word value ;
value = load_var ( var ) - 1 ;
put_var ( var,value ) ;
if ( (signed_word)value < (signed_word)threshold )
ret_value ( TRUE ) ;
else
ret_value ( FALSE ) ;
}
word
load ( mode )
int mode ;
{
/*
** Mode 0 = Immediate Word ;
** Mode 1 = Immediate Byte ;
** Mode 2 = Variable ;
*/
extern word *stack ;
register word var ;
if ( --mode < 0 )
return ( next_word () ) ;
if ( mode == 0 )
return ( (word)next_byte () ) ;
var = next_byte () ;
if ( var == 0 )
return ( *stack++ ) ;
else
return ( load_var ( var ) ) ;
}
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