Class: Spitewaste::CodegenEmitter

Inherits:
Emitter
  • Object
show all
Defined in:
lib/spitewaste/emitters/codegen.rb

Overview

Despite my best efforts to torture it into something vaguely resembling a high-level language, Whitespace is quite simple at bottom; so much so that mapping almost all of its instructions to equivalent C++ code is a relatively straightforward endeavor, so long as we don’t mind using goto.

The only interesting aspect of this approach is how we go about calling into and returning from subroutines. A call instruction generates a goto to the label in its argument and a label immediately after that goto, whose address gets pushed onto a stack of “call sites”. Naturally, a return instruction simply pops the address to jump to by way of a computed goto.

Instance Attribute Summary

Attributes inherited from Emitter

#instructions, #options

Instance Method Summary collapse

Methods inherited from Emitter

#initialize

Constructor Details

This class inherits a constructor from Spitewaste::Emitter

Instance Method Details

#emit(io:) ⇒ Object 



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# File 'lib/spitewaste/emitters/codegen.rb', line 13

def emit io:
  io.puts <<CPP
#include <algorithm>
#include <iostream>
#include <map>
#include <stack>
#include <vector>
#include <gmpxx.h>

using namespace std;
typedef mpz_class num;

vector<num> S;
map<num, num> H;
stack<void *> C;
void *cs;
num n;

num pop() { num c = S.back(); S.pop_back(); return c; }

int main(void) {
CPP
  cs = -1 # call site
  instructions.each do |op, arg|
    io.puts case op
      when :push  ; "S.push_back(#{arg});"
      when :pop   ; "pop();"
      when :dup   ; "S.push_back(S.back());"
      when :swap  ; "reverse(S.end() - 2, S.end());"
      when :copy  ; "S.push_back(S[S.size() - 1 - #{arg}]);"
      when :slide ; "S.erase(S.end() - #{arg} - 1, S.end() - 1);"

      when :add   ; "S[S.size() - 2] += S.back(); S.pop_back();"
      when :sub   ; "S[S.size() - 2] -= S.back(); S.pop_back();"
      when :mul   ; "S[S.size() - 2] *= S.back(); S.pop_back();"
      when :div   ; "{ auto d = pop(); auto n = S.back().get_mpz_t();" +
                    "mpz_fdiv_q(n, n, d.get_mpz_t()); }"
      when :mod   ; "{ auto d = pop(); auto n = S.back().get_mpz_t();" +
                    "mpz_fdiv_r(n, n, d.get_mpz_t()); }"

      when :label ; "L#{arg}:"
      when :jump  ; "goto L#{arg};"
      when :jz    ; "if (!pop()) goto L#{arg};"
      when :jn    ; "if (pop() < 0) goto L#{arg};"
      when :call  ; "C.push(&&C#{cs += 1}); goto L#{arg}; C#{cs}:"
      when :ret   ; "cs = C.top(); C.pop(); goto *cs;"
      when :exit  ; "goto done;"

      when :ichr  ; "H[pop()] = cin.get();"
      when :inum  ; "cin >> n; cin.ignore(); H[pop()] = n;"
      when :ochr  ; "cout << (char) pop().get_ui();"
      when :onum  ; "cout << pop();"
      when :store ; "n = pop(); H[pop()] = n;"
      when :load  ; "S.push_back(H[pop()]);"
    end
  end
  io.puts 'done: return S.size(); }' # punish dirty exit
end