Difference between revisions of "Char"
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An 8 bit ASCII character | An 8 bit ASCII character | ||
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+ | === Default typing === | ||
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+ | {{ElementDefaultTypes}} | ||
== Example == | == Example == |
Revision as of 16:26, 12 January 2013
Contents
Syntax
Char
Semantics
An 8 bit ASCII character
Default typing
In the absence of further type information, the following types are added to the chain:
Example
var i:Char; var r:='a';
In this example variable i is explicitly declared to be of type Char. Variable r is declared and found, via type inference, to also be type Char.
Communication
When a variable is assigned to another, depending on where each variable is allocated to, there may be communication required to achieve this assignment. Table \ref{tab:eltypecomm} details the communication rules in the assignment \emph{assignmed variable := assigning variable}. If the communication is issued from MPMD programming style then this will be one sided. The default communication listed here is guaranteed to be safe, which may result in a small performance hit.
Assigned Variable | Assigning Variable | Semantics |
---|---|---|
multiple[] | multiple[] | local assignment |
single[on[i]] | multiple[] | individual processes write values to process i |
multiple[] | single[on[i]] | individual processes read values from process i |
single[on[i]] | single[on[i]] | local assignment where i==i |
single[on[i]] | single[on[j]] | communication from j to i where i!=j |
Communication Example
var a:Int; var b:Int :: allocated[single[on[2]]]; var p; par p from 0 to 3 { if (p==2) b:=p; a:=b; sync; };
This code will result in each process reading the value of b from process 2 and then writing this into a. As already noted, in absence of allocation information the default of allocating to all processes is used. In this example the variable a can be assumed to additionally have the type allocated[multiple]. Note that communication groups are the same as multiple in this context and share the same semantics. All variables marked multiple are private to their containing process.