Re: [Tinycc-devel] libtcc bug when evaluating math expressions

[david wallin]

Daniel,

I tried to implement my own abs function, not optimal in any way. 
Evaluating  "evaluate_me(-1.0)" gives:

ans1 = 256.000000


cheers,

--david.


8<---------------------------------BEGIN

#include <libtcc.h>
//#include "cc_samples.h"

#include <math.h>

#define TCC19
//#define TCC20

double dabs (double x) {
  return x > 0.0 ? x : -x;
}

int main() {

  char *eval_me =   "#include <math.h>\ndouble evaluate_me(double v) { 
return dabs(v); }\0" ;

#ifdef TCC20
  double (*evaluate_me)(double);
  unsigned long val;
#endif

  TCCState *tcc_state;
  tcc_state = tcc_new();
  tcc_set_output_type(tcc_state, TCC_OUTPUT_MEMORY);
  tcc_add_symbol(tcc_state, "dabs", (unsigned long)&dabs);
  tcc_add_library(tcc_state, "m");

  tcc_compile_string(tcc_state, eval_me);

  tcc_relocate(tcc_state);

#ifdef TCC19
    double (*evaluate_me)(double) = (double 
(*)(double))tcc_get_symbol(tcc_state, "evaluate_me");
#endif
#ifdef TCC20
    tcc_get_symbol(tcc_state, &val, "evaluate_me");
    evaluate_me = (void *)val;
#endif

    printf("ans1 = %f\n", evaluate_me(-1.0));

  return 0;

}

8<---------------------------------END


On Thursday, November 27, 2003, at 04:03 PM, Daniel Glöckner wrote:

> On Thu, Nov 27, 2003 at 01:28:45PM +0000, David Wallin wrote:
> >   char *eval_me =   "double evaluate_me(double x, double v) { return
> > (double) ((-1.0 * x) > v * fabs(v)); }\0" ;
>
> #include <math.h>
>
> fabs is not defined and so defaults to returning an integer in eax
> instead of a double in st0. On exit of fabs(), eax holds an undefined
> value which is then converted to a double and multiplied with v.
> GCC knows about fabs and generates the fabs instruction, even with -O0.
>
>   Daniel