The described embodiments include RunningMAC1P and RunningMAC2P instructions. In the described embodiments, a processor receives a first input vector, a second input vector, a third input vector, and a control vector. Upon executing a RunningMAC1P or a RunningMAC2P instruction, the processor sets a base value equal to a value from an element at a key element position in the first input vector. Next, the processor generates the result vector by, for each element of the result vector to the right of the key element position, setting the element in the result vector equal to a sum of the base value and a result of multiplying a value in each relevant element of the second input vector by a value in a corresponding element of the third input vector, from an element at the key element position to and including a predetermined element in the second input vector.