static void swap() {
int left_var = variable(), right_var = variable();
int reg_one = next_register(), reg_two = next_register();
CodeGen(LOAD, reg_one, left_var, EMPTY_FIELD);
CodeGen(LOAD, reg_two, right_var, EMPTY_FIELD);
CodeGen(STORE, left_var, reg_two, EMPTY_FIELD);
CodeGen(STORE, right_var, reg_one, EMPTY_FIELD);
}
static int expr()
{
int reg, left_reg, right_reg;
switch (token) {
case '+':
next_token();
left_reg = expr();
right_reg = expr();
reg = next_register();
CodeGen(ADD, reg, left_reg, right_reg);
return reg;
case '*':
next_token();
left_reg = expr();
right_reg = expr();
reg = next_register();
CodeGen(MUL, reg, left_reg, right_reg);
return reg;
case '-':
next_token();
left_reg = expr();
right_reg = expr();
reg = next_register();
CodeGen(SUB, reg, left_reg, right_reg);
return reg;
case '0':
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '9':
return digit();
case 'a':
case 'b':
case 'c':
case 'd':
case 'e':
return variable();
default:
ERROR("Symbol %c unknown\n", token);
exit(EXIT_FAILURE);
}
}
static int variable() /* only called for R-values */
{
int reg;
if(!is_identifier(token)){
ERROR("Expected identifier\n");
exit(EXIT_FAILURE);
}
reg = next_register();
CodeGen(LOAD, reg, token, EMPTY_FIELD);
next_token();
return reg;
}
static int variable()
{
int reg;
if (!is_identifier(token)) {
ERROR("Expected identifier\n");
exit(EXIT_FAILURE);
}
reg = next_register();
CodeGen(LOADAI, 0, (token-'a')*4, reg); /* token - 'a' is offset of varible, *4 for byte address */
next_token();
return reg;
}
static int digit()
{
int reg;
if (!is_digit(token)) {
ERROR("Expected digit\n");
exit(EXIT_FAILURE);
}
reg = next_register();
CodeGen(LOADI, to_digit(token), reg, EMPTY_FIELD);
next_token();
return reg;
}
