speed of double-precision divide

[Tim Prince]

Steve White wrote:
>  I was under the misconception that each of these SSE operatons
> was meant to be accomplished in a single clock cycle (although I knew there
> are various other issues.)
> 

Current CPU architectures permit an SSE scalar or parallel multiply and 
add instruction to be issued on each clock cycle.  Completion takes at 
least 4 cycles for add, significantly more for multiply.
The instruction timing tables quote throughput (how many cycles between 
issue) and latency (number of cycles to complete an individual operation).
An even more common misconception than yours is that the extra time 
taken to complete multiply, compared with the time of add, would 
disappear with fused multiply-add instructions.
SSE divide, as has been explained, is not pipelined.   The best way to 
speed up a loop with divide is with vectorization, barring situations 
such as the one you brought up where divide may not actually be a 
necessary part of the algorithm.