Skip to content

fix(math): signed overflow in lcm() and SIGFPE when both inputs are zero #1596

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
newmathphys wants to merge 1 commit into
base: master
Choose a base branch
from
Open

fix(math): signed overflow in lcm() and SIGFPE when both inputs are zero #1596

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
14 changes: 13 additions & 1 deletion math/lcm.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,19 @@ int gcd(int a, int b)
}

// Function to return LCM of two numbers
int lcm(int a, int b) { return (a * b) / gcd(a, b); }
int lcm(int a, int b)
{
// gcd(a, b) == 0 only when both inputs are zero; the division below would
// raise SIGFPE. lcm(0, 0) is conventionally 0.
if (a == 0 || b == 0)
return 0;

// Divide BEFORE multiplying. gcd(a, b) divides a exactly, so the
// intermediate value never exceeds the true LCM: for a = b = 50000 the old
// order computed 50000 * 50000 = 2500000000 (signed overflow, UB in C11)
// even though the answer 50000 fits in int with room to spare.
return (a / gcd(a, b)) * b;
}

// Driver program
int main()
Expand Down
Loading