| 
                    reserve_id_t sub_group_reserve_read_pipe
                ( | pipe gentype pipe, | 
| uint num_packets ) | 
            Reserve num_packets entries for reading from
            pipe. Returns a valid non-zero 
            reservation ID if the reservation is successful and 0 otherwise.
        
            The reserved pipe entries are referred to by indices 
            that go from 0 ... num_packets – 1. 
        
This built-in functions must be encountered by all work-items in a sub-group executing the kernel with the same argument values; otherwise the behavior is undefined. We use the generic type name gentype to indicate the built-in OpenCL C scalar or vector integer or floating-point data types or any user defined type built from these scalar and vector data types can be used as the type for the arguments to the pipe functions listed in table 6.29.
The half scalar and vector types can only be used if the cl_khr_fp16 extension is supported. The double scalar and vector types can only be used if double precision is supported.
Reservations made by a sub-group are ordered in the pipe as they are ordered in the program. Reservations made by different sub-groups that belong to the same work-group can be ordered using sub-group synchronization. The order of sub-group based reservations that belong to different work-groups is implementation defined.
 Copyright © 2007-2013 The Khronos Group Inc. 
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Copyright © 2007-2013 The Khronos Group Inc. 
Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and/or associated documentation files (the
"Materials"), to deal in the Materials without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Materials, and to
permit persons to whom the Materials are furnished to do so, subject to
the condition that this copyright notice and permission notice shall be included
in all copies or substantial portions of the Materials.