Int Mul Overflow

:::info[Note] This is a point-in-time snapshot of the API documentation from January 2026. Going forward, we will not be maintaining a public copy of these references, and recommend users to refer to the built-in signature helpers available in the Hack LSP instead for complete and up-to-date information. :::

Returns the overflow part of multiplying two ints, as if they were unsigned

namespace HH;

function int_mul_overflow(
  int $a,
  int $b,
): int;

In other words, this returns the upper 64 bits of the full product of (unsigned)$a and (unsigned)$b. (The lower 64 bits is just $a * $b regardless of signed/unsigned).

Parameters

• int $a
• int $b

Returns

• int