SWITCH

Switch is an experiment in using ANSI C to target ANSI C switch statements and gotos.

Structure

switch.c A recursive descent compiler which parses switch .sw files. The language of a switch file is reminiscent to the B Programming Language where int (and pointers thereto) are the only types.

examples.sw Various examples exemplifying Switch as a language.

tests.sw Unit tests, tests operators, and basic expressions and statements.

Use

run make to build switch, which will the use switch to compile .sw files into intermediate .c files that gcc then compiles into native executables. The makefile will also output the corresponding .asm of each executable for fun.

An example (see more in examples.sw) of a switch program:

int factorial(int x)
{
    if(x == 0)
    {
        ret 1;
    }
    else
    {
        ret x * factorial(x - 1);
    }
}

int main()
{
    if(factorial(9) == 362880)
    {
        ret 0;
    }
    else
    {
        ret 1;
    }
}

The output generates an intermediate (.c) that when (post processed) translates directly to a stack machine that abuses gotos for branching and switch statements for calling functions returning from functions:

int main(void) {
 int fs[4096] = { 0 };
 int bs[4096] = { 0 };
 int vs[65536] = { 0 };
 register int fp = 1;
 register int fa = 0;
 register int sp = 0;
 register int rr = 0;
 goto main;
begin:
 if(fp == 0)
  return vs[sp - 1];
 switch(fa)
 {
factorial:
 vs[sp++] = 0 + bs[fp - 1];
 vs[sp - 1] = vs[vs[sp - 1]];
 vs[sp++] = 0;
 vs[sp - 2] = vs[sp - 2] == vs[sp - 1]; --sp;
 if(vs[--sp] == 0) goto L0;
 vs[sp++] = 1;
 rr = vs[sp - 1];--fp;sp = bs[fp];fa = fs[fp];vs[sp] = rr;sp++;goto begin;
 goto L1;
L0:
 vs[sp++] = 0 + bs[fp - 1];
 vs[sp - 1] = vs[vs[sp - 1]];
 bs[fp] = sp;
 vs[sp++] = 0 + bs[fp - 1];
 vs[sp - 1] = vs[vs[sp - 1]];
 vs[sp++] = 1;
 vs[sp - 2] -= vs[sp - 1]; --sp;
 fs[fp] = 64;fp++;goto factorial;case 64:;
 vs[sp - 2] *= vs[sp - 1]; --sp;
 rr = vs[sp - 1];--fp;sp = bs[fp];fa = fs[fp];vs[sp] = rr;sp++;goto begin;
L1:
 --sp;
 vs[sp++] = 0;
 rr = vs[sp - 1];--fp;sp = bs[fp];fa = fs[fp];vs[sp] = rr;sp++;goto begin;
main:
 bs[fp] = sp;
 vs[sp++] = 9;
 fs[fp] = 74;fp++;goto factorial;case 74:;
 vs[sp++] = 362880;
 vs[sp - 2] = vs[sp - 2] == vs[sp - 1]; --sp;
 if(vs[--sp] == 0) goto L2;
 vs[sp++] = 0;
 rr = vs[sp - 1];--fp;sp = bs[fp];fa = fs[fp];vs[sp] = rr;sp++;goto begin;
 goto L3;
L2:
 vs[sp++] = 1;
 rr = vs[sp - 1];--fp;sp = bs[fp];fa = fs[fp];vs[sp] = rr;sp++;goto begin;
L3:
 vs[sp++] = 0;
 rr = vs[sp - 1];--fp;sp = bs[fp];fa = fs[fp];vs[sp] = rr;sp++;goto begin;
 }
 return 0;
}