By: Paul A. Clayton (paaronclayton.delete@this.gmail.com), February 25, 2013 8:57 am
Room: Moderated Discussions
Wilco (Wilco.Dijkstra.delete@this.ntlworld.com) on February 25, 2013 5:54 am wrote:
[snip]
> So that proves that for compiled code having 1 condition bit is just as powerful as having 4 (or 100...).
On the other hand, does having three more bits make that much difference? The utility of the extra bits does not need to be especially great if the extra complexity and resource use is especially small. (Sign test is trivial, carry and overflow determination are not that complex; and communication and storage of four bits is not that much more complex than that of one bit--much of the overhead is in control not the size of the value.)
Non-compiled code might also have some influence on ISA design. (It is also possible that in the lifetime of the ISA language/compiler/programmer support for uses of multiple bits might increase--not likely, it seems, for general purpose code as there seems to be a trend toward more abstraction/less specificity, but some side use might be considered important by the ISA designers.)
The SIMD use for "all, none, most/many, one" might make 4-bit conditions more useful.
[snip]
> So that proves that for compiled code having 1 condition bit is just as powerful as having 4 (or 100...).
On the other hand, does having three more bits make that much difference? The utility of the extra bits does not need to be especially great if the extra complexity and resource use is especially small. (Sign test is trivial, carry and overflow determination are not that complex; and communication and storage of four bits is not that much more complex than that of one bit--much of the overhead is in control not the size of the value.)
Non-compiled code might also have some influence on ISA design. (It is also possible that in the lifetime of the ISA language/compiler/programmer support for uses of multiple bits might increase--not likely, it seems, for general purpose code as there seems to be a trend toward more abstraction/less specificity, but some side use might be considered important by the ISA designers.)
The SIMD use for "all, none, most/many, one" might make 4-bit conditions more useful.
