Public bug reported:
If I compile the code using g++ and -O2 optimization and try the algorithm
with this input "10000 100 10" I get a wrong answer.
I can get the correct solution if I compile the same code don't using any
optimization.
#include <algorithm>
#include <cstdlib>
#include <cstdio>
#include <cmath>
using namespace std;
#define DEBUG
struct Point
{
double x, y;
Point() : x(0), y(0) {}
Point(const double _x, const double _y) : x(_x), y(_y) {}
};
struct Retta
{
double x, y, z;
Retta() : x(0), y(0), z(0) {}
Retta(const Point& p1, const double m)
{
// y - y1 = m(x - x1)
x = m;
y = -1;
z = p1.y-m*p1.x;
}
Retta(const Point& p1, const Point& p2)
{
if (p1.x == p2.x)
{
x = 1;
y = 0;
z = -p1.x;
}
else if (p1.y == p2.y)
{
x = 0;
y = 1;
z = -p1.y;
}
else
{
double m = (p1.y-p2.y)/(p1.x-p2.x);
x = m;
y = -1;
z = p1.y-m*p1.x;
}
}
};
Point p1, p2, p3;
Retta r1, r2;
const double EPS = 1E-6;
int solve()
{
int sols = 0;
double x1, x2;
for (int i = 1; i < p2.y; i++)
{
x1 = ((-r1.y*i-r1.z)/r1.x);
x2 = ((-r2.y*i-r2.z)/r2.x);
x1 = (ceil(x1) == x1 ? x1+1 : ceil(x1));
x2 = (floor(x2) == x2 ? x2-1: floor(x2));
sols += static_cast<int>(x2-x1+1);
#ifdef DEBUG
printf("level %d = [%lf, %d] [%lf, %d] D = %lf [%d]\n", i, x1, i, x2,
i, x2-x1+1, sols);
#endif
}
return sols;
}
void read(FILE* in)
{
int a, b, c;
fscanf(in, "%d%d%d", &a, &b, &c);
p1 = Point(0, 0);
p2 = Point(a, b);
p3 = Point(c, 0);
r1 = Retta(p1, p2);
r2 = Retta(p3, p2);
#ifdef DEBUG
printf("R1: %lf x + %lf y + %lf = 0\n", r1.x, r1.y, r1.z);
printf("R2: %lf x + %lf y + %lf = 0\n", r2.x, r2.y, r2.z);
#endif
}
int main()
{
FILE* in = fopen("fence9.in", "r");
FILE* out = fopen("fence9.out", "w");
#ifdef DEBUG
in = stdin;
out = stdout;
#endif
read(in);
fprintf(out, "%d\n", solve());
return 0;
}
** Affects: Ubuntu
Importance: Undecided
Status: Unconfirmed
--
Seem optimization -O2 don't work g++
https://launchpad.net/bugs/82190
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