gcc_710_mwe.c

// To see correct behavior, run the output of:
//   gcc -o gcc_710_mwe -O1             -Wall -Werror -march=pentium4 -m32 -fno-gnu89-inline -fno-builtin -std=c99 -fPIC gcc_710_mwe.c
// To see broken behavior, run the output of:
//   gcc -o gcc_710_mwe -O1 -fpeephole2 -Wall -Werror -march=pentium4 -m32 -fno-gnu89-inline -fno-builtin -std=c99 -fPIC gcc_710_mwe.c

typedef union {
  double value;
  struct {
    int lsw;
    int msw;
  } parts;
} ieee_double_shape_type;
double a, b = -3.25565818622400915405e-01, c = -4.00555345006794114027e-02,
          d = -2.40339491173441421878e00, e = -6.88283971605453293030e-01, p, q,
          r, t, u, v, w;
int f, g, h, i, j, l, x;
unsigned k, m;
ieee_double_shape_type n, o;
double fn1(double p1) {
  n.value = p1;
  f = n.parts.msw;
  l = n.parts.lsw;
  i = n.parts.msw >> 20;
  i -= 1023;
  f = (f & 1048575) | 1048576;
  i >>= 1;
  f += f + (2147483648 >> 31);
  l += l;
  k = 2097152;
  while (k) {
    j = g + k;
    if (j <= f) {
      g = j + k;
      f -= j;
      h += k;
    }
    f += f + ((l & 2147483648) >> 31);
    l += l;
    k >>= 1;
  }
  k = 2147483648;
  while (k) {
    j = g;
    if (j < f) {
      g++;
      f -= j;
      m += k;
    }
    f += f;
    k >>= 1;
  }
  f = (h >> 1) + 1071644672;
  l = m >> 1;
  f += i << 20;
  o.parts.msw = f;
  o.parts.lsw = l;
  return o.value;
}
double fn2(double p1) {
  double s;
  if (x)
    return a * t;
  p = (1.00000000000000000000e00 - p1) * 0.5;
  s = fn1(p);
  ieee_double_shape_type z;
  z.value = s;
  z.parts.lsw = 0;
  w = z.value;
  v = (p - z.value * z.value) / (s + z.value);
  q = p * (1.66666666666666657415e-01 +
           p * (b +
                p * (2.01212532134862925881e-01 +
                     p * (c +
                          p * (7.91534994289814532176e-04 +
                               p * 3.47933107596021167570e-05)))));
  r = 1.00000000000000000000e00 +
      p * (d +
           p * (2.02094576023350569471e00 +
                p * (e + p * 7.70381505559019352791e-02)));
  t = q / r;
  u = t * s + v;
  return 2.0 * (z.value + u);
}
void printf();
int main() {
  double y = fn2(0.8);
  printf("%.16f\n", y);
}