/* stack operator
**nest**
> Creates a fresh stack with current TOS on it. Saves current dstack onto
> rstack.
*/
bvm_cache *nest(bvm_cache *this_bvm){ // nest#
mword *nest_body = dstack_get(this_bvm,0);
// mword *new_stack = dstack_get(this_bvm,1);
mword *save_TOS = dstack_get(this_bvm,1);
popd(this_bvm);
popd(this_bvm);
mword *save_dstack = (mword*)icar(this_bvm->dstack_ptr);
mword *save_ustack = (mword*)icar(this_bvm->ustack_ptr);
clear(this_bvm); // clear the stack
//rgive(this_bvm, new_stack);
pushd(this_bvm, save_TOS, IMMORTAL);
mword *nest_return = (mword*)icdr(icar(this_bvm->code_ptr));
mword *nest_rstack_entry = consa2(this_bvm, save_dstack,
consa2(this_bvm, save_ustack,
consa2(this_bvm, nest_return, nil)));
pushr(this_bvm, nest_rstack_entry, _hash8(C2B("/babel/tag/nest")));
this_bvm->code_ptr = consa2(this_bvm, nest_body,nil);
icar(this_bvm->advance_type) = BVM_CONTINUE;
return this_bvm;
}
void main()
{
char prefix[50],ch,str[50],operand1[50],operand2[50],oper_ator[2];
int i=0,k=0,opndcnt=0;
clrscr();
printf("\t\t\t * Prefix to Postfix *");
printf("\n\nEnter the Prefix Expression : ");
gets(prefix);
while((ch=prefix[i++])!='\0')
{
if(isalnum(ch))
{
str[0]=ch;
str[1]='\0';
pushd(str);
operand_count++;
if(operand_count>=2)
{
strcpy(operand2,popd());
strcpy(operand1,popd());
strcpy(str,operand1);
strcat(str,operand2);
ch=popr();
oper_ator[0]=ch;
oper_ator[1]='\0';
strcat(str,oper_ator);
pushd(str);
operand_count-=1;
}
}
else
{
pushr(ch);
/* operator followed by single operand*/
if(operand_count==1)
operand_count=0;
}
}
if(!empty(topd))
{
strcpy(operand2,popd());
strcpy(operand1,popd());
strcpy(str,operand1);
strcat(str,operand2);
ch=popr();
oper_ator[0]=ch;
oper_ator[1]='\0';
strcat(str,oper_ator);
pushd(str);
}
printf("The Postfix Expression is : ");
puts(opnds[topd]);
getch();
}
/* This function does all of lexing, parsing, and picking a good
order of evaluation... Needless to say, this is not the best
possible design, but it avoids cluttering everything with globals. */
pifi
compile_rpn (char *expr)
{
struct stack_element stack[32];
int sp = 0;
int curr_tos = -1; /* stack element currently in R0 */
int spill_base, spill_sp;
pifi fn;
int ofs;
fn = (pifi) (jit_get_ip ().iptr);
jit_leaf (1);
ofs = jit_arg_i ();
spill_sp = spill_base = jit_allocai (32 * sizeof (int));
while (*expr)
{
int with_imm;
int imm;
int tok;
int src1, src2;
/* This is the lexer. */
switch (*expr)
{
case ' ': case '\t':
expr++;
continue;
case '0': case '1': case '2': case '3': case '4':
case '5': case '6': case '7': case '8': case '9':
stack[sp].kind = IMM;
stack[sp++].imm = strtol (expr, &expr, 0);
continue;
case 'x':
expr++;
stack[sp++].kind = ARG;
continue;
case '~':
/* NOT. Implemented as a XOR with -1. */
stack[sp].kind = IMM;
stack[sp++].imm = ~0;
tok = '^';
break;
case '_':
/* Unary minus. Transform to 0 - X and go on.
Also used to enter negative constants (32_ = -32). */
expr++;
stack[sp] = stack[sp - 1];
/* Ensure CURR_TOS is correct. */
if (curr_tos == sp - 1)
curr_tos = sp;
stack[sp - 1].kind = IMM;
stack[sp - 1].imm = 0;
sp++;
tok = '-';
break;
case '+':
case '-':
case '*':
case '/':
case '%':
case '&':
case '|':
case '^':
case '=':
tok = *expr++;
break;
case '!':
/* Get != */
expr++;
assert (*expr == '=');
tok = NE;
break;
case '<':
/* Get <, <<, <= */
if (expr[1] == '=')
expr += 2, tok = LE;
else if (expr[1] == '<')
expr += 2, tok = LSH;
else
expr++, tok = '<';
break;
case '>':
/* Get >, >>, >>>, >= */
if (expr[1] == '=')
expr += 2, tok = GE;
else if (expr[1] == '>' && expr[2] == '>')
expr += 3, tok = RSHU;
else if (expr[1] == '>')
expr += 2, tok = RSH;
else
expr++, tok = '>';
break;
default:
abort ();
}
assert (sp >= 2);
/* Constant folding. */
if (stack[sp - 1].kind == IMM && stack[sp - 2].kind == IMM)
{
stack[sp - 2].imm =
fold (stack[sp - 2].imm, stack[sp - 1].imm, tok);
sp--;
continue;
}
/* If possible, ensure that the constant is the RHS, possibly
by changing TOK (if it is a comparison). */
if (stack[sp - 2].kind == IMM)
{
int swapped_operation = swap_op (tok);
if (swapped_operation)
{
tok = swapped_operation;
stack[sp - 2].kind = stack[sp - 1].kind;
stack[sp - 1].kind = IMM;
stack[sp - 1].imm = stack[sp - 2].imm;
/* Ensure CURR_TOS is correct. */
if (curr_tos == sp - 1)
curr_tos = sp - 2;
}
}
/* Get the second argument into a register, if not an immediate.
Also decide which argument will be prepared into JIT_R0 and
which will be prepared into JIT_V0. */
with_imm = 0;
src1 = JIT_R0;
src2 = JIT_V0;
switch (stack[sp - 1].kind)
{
case IMM:
/* RHS is an immediate, use an immediate instruction. */
with_imm = 1;
imm = stack[sp - 1].imm;
break;
case EXPR:
/* RHS is an expression, check if it is already in JIT_R0. */
if (curr_tos == sp - 1)
{
/* Invert the two sources. */
src1 = JIT_V0;
src2 = JIT_R0;
}
else
popr (JIT_V0, &spill_sp);
curr_tos = -1;
break;
case ARG:
jit_getarg_i (JIT_V0, ofs);
break;
}
/* Get the first argument into a register indicated by SRC1. */
switch (stack[sp - 2].kind)
{
case IMM:
/* LHS is an immediate, check if we must spill the top of stack. */
if (curr_tos != -1)
{
pushr (JIT_R0, &spill_sp);
curr_tos = -1;
}
jit_movi_i (src1, stack[sp - 2].imm);
break;
case EXPR:
/* LHS is an expression, check if it is already in JIT_R0. */
if (curr_tos != sp - 2)
{
popr (src1, &spill_sp);
curr_tos = -1;
}
else
assert (src1 == JIT_R0);
break;
case ARG:
if (curr_tos != -1)
{
pushr (JIT_R0, &spill_sp);
curr_tos = -1;
}
jit_getarg_i (src1, ofs);
break;
}
/* Set up the new stack entry, which is cached in R0. */
sp -= 2;
curr_tos = sp;
stack[sp++].kind = EXPR;
/* Perform the computation. */
if (with_imm)
gen_reg_imm (src1, imm, tok);
else
gen_reg_reg (src1, src2, tok);
}
assert (sp == 1);
switch (stack[0].kind)
{
case IMM:
jit_movi_i (JIT_RET, stack[0].imm);
break;
case EXPR:
assert (curr_tos == 0);
jit_movr_i (JIT_RET, JIT_R0);
break;
case ARG:
jit_getarg_i (JIT_V0, ofs);
break;
}
jit_ret ();
jit_flush_code ((char *) fn, jit_get_ip ().ptr);
#ifdef LIGHTNING_DISASSEMBLE
disassemble (stderr, (char *) fn, jit_get_ip ().ptr);
#endif
return fn;
}
