Solving cubic equations 2

Write a program that finds every real root of the cubic equation $Ax^3 + Bx^2 + Cx + D = 0$.

Every equation in the input has at least one integer root.

The absolute value of $A$, $B$, $C$, and $D$ is at most $2 \times 10^6$, and $A$ is not zero. Every real root has absolute value at most $10^6$. $A$, $B$, $C$, and $D$ can carry up to 11 digits after the decimal point. Within one equation, two different roots differ by more than $10^{-9}$.

The first line contains the number of test cases $N$ ($0 < N < 100$). Each of the next $N$ lines contains the coefficients $A$, $B$, $C$, and $D$ of one equation, separated by spaces.

For each equation, print all of its real roots in ascending order on one line. Separate two roots with a single space and round each root to four digits after the decimal point. Print a multiple root only once. If a root rounds to zero, print 0.0000 and not -0.0000.