Re: Doubt about formula transcription

On Jun 27, 9:01 pm, "robin" <robi...@xxxxxxxxxxx> wrote:
"glen herrmannsfeldt" <g...@xxxxxxxxxxxxxxxx> wrote in message

news:9NidnaRYwaLYNGbanZ2dnUVZ_o3inZ2d@xxxxxxxxxxxxxx

Constant folding yes, but commutativity and associativity
are different. (Especially on Cray machines where
A*B wasn't always equal to B*A, as stories go.)

And why would they be different?

The Cray-1 series did not compute all of the trailing bits of
a floating-point product. On the first Cray-1's, the bits
chosen were not symmetric and so the multiplication was not
commutative. On the Cray-1s and later machines, the bits chosen
were commutative. The advantages of not computing some of the
product bits were that the machine was cheaper to build (though
hardly cheap) and the multiplication instruction was faster.

Bob Corbett
.