imul32 function

  1. @Since.new("3.15")
int imul32(
  1. int a,
  2. int b
)

Returns the 32-bit signed wrapping product of a and b.

Truncates a and b to 32-bit integers, multiplies them modulo 2^32, and returns the low 32 bits of the product as a signed integer in the range -2^31 to 2^31 - 1 ((a * b).toSigned(32) in 64-bit integer arithmetic).

Because signed and unsigned 32-bit wrapping multiplication produce the same low 32 bits, use imul32(a, b).toUnsigned(32) when an unsigned 32-bit result in 0 to 2^32 - 1 is needed.

Differences between JavaScript and 64-bit runtimes

On JavaScript runtimes, a * b is evaluated using 64-bit floating-point arithmetic (double). When the exact product of two 32-bit integers exceeds 2^53, (a * b).toSigned(32) and (a * b) & 0xFFFFFFFF lose the low-order bits due to rounding in the floating-point multiply before truncation to 32 bits. This function computes the exact low 32 bits without rounding, using Math.imul(a, b) when running on a JavaScript runtime.

Implementation

@Since("3.15")
external int imul32(int a, int b);