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Cray Standard C/C++ Reference Manual

The formats of these directives are as follows:

#pragma _CRI shortloop

#pragma _CRI shortloop128

The following examples illustrate the use of the shortloop and shortloop128

directives:

#pragma _CRI shortloop

for (i = 0; i < n; i++) { /* 1< = n < = 64 */

a[i] = b[i] + c[i];

}

#pragma _CRI shortloop128

for (i = 0; i < n; i++) { /* 1 < = n < = 128 */

a[i] = b[i] + c[i];

}

3.8 Tasking Directives

The Cray Standard C/C++ compilers support parallel processing using

multiple processors on UNICOS systems. Parallel processing is a technique

that breaks a computational task into a set of subtasks and then performs each

subtask simultaneously. This allows many jobs to run faster by spreading a

computational task across multiple processors. The increase in speed of execution

depends on the degree of parallelism that is inherent in the program. See

Optimizing Application Code on UNICOS Systems, for more information.

Tasking can be performed automatically by the compiler (Autotasking) or it can

be directed by the user (user-directed tasking). The methods that can be used to

accomplish tasking are defined as follows:

• Autotasking is performed automatically by the compiler based on its analysis

of the code.

Autotasking automates loop-level tasking by detecting parallelism in a

program and exploiting the parallelism without user intervention. You can

add directives to your code that identify loops you know can be tasked and

depend upon Autotasking to analyze other loops.

Generally, Autotasking works best on programs in which most of the work is

in nested loops that do not contain function calls.

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Vax C90-EL SERIES Service Manual Page 82