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/* $Id: operand.c,v 1.2 2000/05/25 22:28:56 jholder Exp $
* --------------------------------------------------------------------
* see doc/License.txt for License Information
* --------------------------------------------------------------------
*
* File name: $Id: operand.c,v 1.2 2000/05/25 22:28:56 jholder Exp $
*
* Description:
*
* Modification history:
* $Log: operand.c,v $
* Revision 1.2 2000/05/25 22:28:56 jholder
* changes routine names to reflect zmachine opcode names per spec 1.0
*
* Revision 1.1.1.1 2000/05/10 14:21:34 jholder
*
* imported
*
*
* --------------------------------------------------------------------
*/
/*
* operand.c
*
* Operand manipulation routines
*
*/
#include "ztypes.h"
/*
* load_operand
*
* Load an operand, either: a variable, popped from the stack or a literal.
*
*/
zword_t load_operand( int type )
{
zword_t operand;
if ( type )
{
/* Type 1: byte literal, or type 2: operand specifier */
operand = ( zword_t ) read_code_byte( );
if ( type == 2 )
{
/* If operand specifier non-zero then it's a variable, otherwise
* it's the top of the stack */
if ( operand )
{
return load_variable( operand );
}
else
{
return stack[sp++];
}
}
}
else
{
/* Type 0: word literal */
return read_code_word( );
}
return ( operand );
} /* load_operand */
/*
* store_operand
*
* Store an operand, either as a variable pushed on the stack.
*
*/
void store_operand( zword_t operand )
{
zbyte_t specifier;
/* Read operand specifier byte */
specifier = read_code_byte( );
/* If operand specifier non-zero then it's a variable, otherwise it's the
* pushed on the stack */
if ( specifier )
z_store( specifier, operand );
else
stack[--sp] = operand;
} /* store_operand */
/*
* load_variable
*
* Load a variable, either: a stack local variable, a global variable or
* the top of the stack.
*
*/
zword_t load_variable( int number )
{
if ( number )
{
if ( number < 16 )
{
/* number in range 1 - 15, it's a stack local variable */
return stack[fp - ( number - 1 )];
}
else
{
/* number > 15, it's a global variable */
return get_word( h_globals_offset + ( ( number - 16 ) * 2 ) );
}
}
else
{
/* number = 0, get from top of stack */
return stack[sp];
}
} /* load_variable */
/*
* z_store
*
* Store a variable, either: a stack local variable, a global variable or the
* top of the stack.
*
*/
void z_store( int number, zword_t variable )
{
if ( number )
{
if ( number < 16 )
/* number in range 1 - 15, it's a stack local variable */
stack[fp - ( number - 1 )] = variable;
else
/* number > 15, it's a global variable */
set_word( h_globals_offset + ( ( number - 16 ) * 2 ), variable );
}
else
/* number = 0, get from top of stack */
stack[sp] = variable;
} /* z_store */
/*
* z_piracy
*
* Supposed to jump if the game thinks that it is pirated.
*/
void z_piracy( int flag )
{
conditional_jump( flag );
}
/*
* conditional_jump
*
* Take a jump after an instruction based on the flag, either true or false. The
* jump can be modified by the change logic flag. Normally jumps are taken
* when the flag is true. When the change logic flag is set then the jump is
* taken when flag is false. A PC relative jump can also be taken. This jump can
* either be a positive or negative byte or word range jump. An additional
* feature is the return option. If the jump offset is zero or one then that
* literal value is passed to the return instruction, instead of a jump being
* taken. Complicated or what!
*
*/
void conditional_jump( int flag )
{
zbyte_t specifier;
zword_t offset;
/* Read the specifier byte */
specifier = read_code_byte( );
/* If the reverse logic flag is set then reverse the flag */
if ( specifier & 0x80 )
flag = ( flag ) ? 0 : 1;
/* Jump offset is in bottom 6 bits */
offset = ( zword_t ) specifier & 0x3f;
/* If the byte range jump flag is not set then load another offset byte */
if ( ( specifier & 0x40 ) == 0 )
{
/* Add extra offset byte to existing shifted offset */
offset = ( offset << 8 ) + read_code_byte( );
/* If top bit of offset is set then propogate the sign bit */
if ( offset & 0x2000 )
offset |= 0xc000;
}
/* If the flag is false then do the jump */
if ( flag == 0 )
{
/* If offset equals 0 or 1 return that value instead */
if ( offset == 0 || offset == 1 )
{
z_ret( offset );
}
else
{ /* Add offset to PC */
pc = ( unsigned long ) ( pc + ( ZINT16 ) offset - 2 );
}
}
} /* conditional_jump */
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