Fix mandelbrot microbenchmark in C, Fortran and Go

Now they produce correct value consistent with Julia version. Discrepancy have existed due to error accumulation in floating-point loops and inaccuracy in cpow function (for C).

test/perf/micro/perf.c

@@ -62,16 +62,16 @@ int mandel(double complex z) {
  if (cabs(z) > 2.0) {
  return n;
  }
- z = cpow(z,2)+c;
+ z = z*z+c;
  }
  return maxiter;
 }
 
 int mandelperf() {
  int mandel_sum = 0;
- for (double re=-2.0; re<=0.5; re+=0.1) {
- for (double im=-1.0; im<=1.0; im+=0.1) {
- int m = mandel(re+im*I);
+ for (int re=-20; re<=5; re+=1) {
+ for (int im=-10; im<=10; im+=1) {
+ int m = mandel(re/10.0+I*im/10.0);
  mandel_sum += m;
  }
  }
@@ -286,7 +286,7 @@ int main() {
  t = clock_now()-t;
  if (t < tmin) tmin = t;
  }
- assert(mandel_sum == 14719);
+ assert(mandel_sum == 14791);
  print_perf("mandel", tmin);
 
  // sort

test/perf/micro/perf.f90

@@ -196,16 +196,16 @@ integer function mandel(z0) result(r)
 end function
 
 integer function mandelperf() result(mandel_sum)
-real(dp) :: re, im
+integer :: re, im
 mandel_sum = 0
-re = -2._dp
-do while (re <= 0.5_dp)
- im = -1._dp
- do while (im <= 1._dp)
- mandel_sum = mandel_sum + mandel(cmplx(re, im, dp))
- im = im + 0.1_dp
+re = -20
+do while (re <= 5)
+ im = -10
+ do while (im <= 10)
+ mandel_sum = mandel_sum + mandel(cmplx(re/10._dp, im/10._dp, dp))
+ im = im + 1
  end do
- re = re + 0.1_dp
+ re = re + 1
 end do
 end function
 
@@ -346,9 +346,7 @@ program perf
  call cpu_time(t2)
  if (t2-t1 < tmin) tmin = t2-t1
 end do
-! This number is processor dependent, as it can differ a bit depending on the
-! floating point rounding errors:
-!call assert(f == 14307)
+call assert(f == 14791)
 print "('fortran,mandel,',f0.6)", tmin*1000._dp / NRUNS
 
 tmin = 1e9_dp

test/perf/micro/perf.go

@@ -82,9 +82,9 @@ func mandel(z complex128) int {
 
 func mandelperf() int {
  mandel_sum := 0
- for re := -2.0; re <= 0.5; re += 0.1 {
- for im := -1.0; im <= 1.0; im += 0.1 {
- m := mandel(complex(re, im))
+ for re := -20; re <= 5; re += 1 {
+ for im := -10; im <= 10; im += 1 {
+ m := mandel(complex(float64(re)/10, float64(im)/10))
  mandel_sum += m
  }
  }
@@ -145,8 +145,7 @@ func main() {
  }
  print_perf("parse_int", tmin)
 
- // fmt.Println(mandelperf())
- // FIXME: assert(mandelperf() == 14791)
+ assert(mandelperf() == 14791)
  tmin = float64(math.MaxFloat64)
  for i := 0; i < 5; i++ {
  t := time.Now()