#include <bits/stdc++.h>
using namespace std;
namespace fast_io {
char buf[1 << 12], *p1 = buf, *p2 = buf, sr[1 << 23], z[23], nc;
int C = -1, Z = 0, Bi = 0, ny;
inline char gc() {
  return p1 == p2 && (p2 = (p1 = buf) + fread(buf, 1, 1 << 12, stdin), p1 == p2)
             ? EOF
             : *p1++;
}
inline long long read() {
  long long x = 0;
  ny = 1;
  while (nc = gc(), (nc < 48 || nc > 57) && nc != EOF)
    if (nc == 45) ny = -1;
  Bi = 1;
  if (nc < 0) return nc;
  x = nc - 48;
  while (nc = gc(), 47 < nc && nc < 58 && nc != EOF)
    x = (x << 3) + (x << 1) + (nc ^ 48), Bi++;
  return x * ny;
}
inline double find() {
  int a = read(), y = ny, b = (nc != '.') ? 0 : read();
  return (b ? a + (double)b / pow(10, Bi) * y : a);
}
inline int gs(char *s) {
  char c, *t = s;
  while (c = gc(), c <= 32)
    ;
  *s++ = c;
  while (c = gc(), c > 32) *s++ = c;
  return s - t;
}
inline void ot() {
  fwrite(sr, 1, C + 1, stdout);
  C = -1;
}
inline void flush() {
  if (C > 1 << 22) ot();
}
template <typename T>
inline void write(T x, char t) {
  int y = 0;
  if (x < 0) y = 1, x = -x;
  while (z[++Z] = x % 10 + 48, x /= 10)
    ;
  if (y) z[++Z] = '-';
  while (sr[++C] = z[Z], --Z)
    ;
  sr[++C] = t;
  flush();
}
inline void write(char *s) {
  int l = strlen(s);
  for (int i = 0; i < l; i++) sr[++C] = *s++;
  sr[++C] = '\n';
  flush();
}
}  // namespace fast_io
using namespace fast_io;
long long t, a, b, p, q, len;
inline long long calc(long long a, long long b, long long c, long long n) {
  if (!a || !n) return (n + 1) * (b / c);
  if (n < 0) return 0;
  long long m = (a * n + b) / c;
  if (a >= c || b >= c)
    return calc(a % c, b % c, c, n) + (n * (n + 1) >> 1) * (a / c) +
           (n + 1) * (b / c);
  return n * m - calc(c, c - b - 1, a, m - 1);
}
inline long long exgcd(long long a, long long b, long long &x, long long &y) {
  if (!b) return x = 1, y = 0, a;
  long long d = exgcd(b, a % b, y, x);
  return y -= a / b * x, d;
}
int main() {
  t = read();
  while (t--) {
    a = read(), b = read(), p = read(), q = read();
    long long l = 0, r = q, m, s = p << 1, t = q << 1;
    while (l < r) {
      m = (l + r) >> 1;
      long long L = q - m, R = q + m + 1;
      calc(s, t - L, t, b) + calc(s, t - R, t, a - 1) -
                  calc(s, t - L, t, a - 1) - calc(s, t - R, t, b) >
              0
          ? r = m
          : l = m + 1;
    }
    long long x, y, d = exgcd(s, t, x, y), ans = 1e9;
    s /= d, t /= d;
    if ((q - l) % d == 0) {
      long long v = (q - l) / d * x;
      v += (a - v) / t * t;
      while (v >= a) v -= t;
      while (v < a) v += t;
      ans = min(ans, v);
    }
    if ((q + l) % d == 0) {
      long long v = (q + l) / d * x;
      v += (a - v) / t * t;
      while (v >= a) v -= t;
      while (v < a) v += t;
      ans = min(ans, v);
    }
    write(ans, '\n');
    ot();
  }
  return ot(), 0;
}
