mulMod(_:modulus:)

Returns (self * other) % modulus.

iOS 18.0+
macCatalyst 18.0+
macOS 15.0+
tvOS 18.0+
visionOS 2.0+
watchOS 11.0+

func mulMod(_ other: UInt256, modulus: UInt256) -> UInt256

Parameters

other: The value to multiply.
modulus: The modulus (must be non-zero).

Return Value

(self * other) mod modulus.

Discussion

Computes the full 512-bit intermediate via multipliedFullWidth(by:) and reduces with a single dividingFullWidth call. Assumes both operands are already reduced modulo modulus (self < modulus and other < modulus) so the intermediate does not overflow the 512-bit (high, low) tuple when modulus is near 2^256.

Precondition

modulus != 0, self < modulus, other < modulus.