Double

Syntax

Double

Semantics

A double precision 64 bit floating point number. This is the type given to constant floating point numbers that appear in program code.

Default typing

In the absence of further type information, the following types are added to the chain:

• allocated
• multiple
• stack
• onesided

Example

function void main() {
   var i:Double;
};

In this example variable i is explicitly declared to be of type Double.

Since: Version 0.41b

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.