Itanium® Architecture for Programmers: Understanding 64-Bit Processors and EPIC Principles

5.4. DOTLOOP: Using a Counted Loop

In the previous chapter, we presented the DOTPROD program that computed the dot product of two 3-component vectors without using a loop. A similar program, but with greater generality, would compute the dot product of two N-component vectors. Such a program, with the dimensionality N as a symbolic parameter at the top of the listing, is presented in Figure 5-1.

This more general program uses additional registers: r17 for the dimensionality and loop control, r14 as an address pointer for vector V , r15 as an address pointer for vector W , and r16 as an address pointer for the product P. While there is a little more overhead between first and top to get everything set up, the heart of the algorithm is simplified ...