NAME

       Reinterpreting_Types_Using_as_type()_and_as_typen()

       as_type()
       as_typen()

DESCRIPTION

       All data types described in scalarDataTypes(3clc) and vectorDataTypes(3clc) (except bool,
       half (unless the cl_khr_fp16(3clc) extension is supported), and void) may be also
       reinterpreted as another data type of the same size using the as_type() operator for
       scalar data types and the as_typen() operator for vector data types. When the operand and
       result type contain the same number of elements, the bits in the operand shall be returned
       directly without modification as the new type. The usual type promotion for function
       arguments shall not be performed.

       For example, as_float(0x3f800000) returns 1.0f, which is the value that the bit pattern
       0x3f800000 has if viewed as an IEEE-754 single precision value.

       When the operand and result type contain a different number of elements, the result shall
       be implementation-defined except if the operand is a 4-component vector and the result is
       a 3-component vector. In this case, the bits in the operand shall be returned directly
       without modification as the new type. That is, a conforming implementation shall
       explicitly define a behavior, but two conforming implementations need not have the same
       behavior when the number of elements in the result and operand types does not match. The
       implementation may define the result to contain all, some or none of the original bits in
       whatever order it chooses. It is an error to use the as_type() or as_typen() operators to
       reinterpret data to a type of a different number of bytes.

NOTES

       While the union is intended to reflect the organization of data in memory, the as_type()
       and as_typen() constructs are intended to reflect the organization of data in register.
       The as_type() and as_typen() constructs are intended to compile to no instructions on
       devices that use a shared register file designed to operate on both the operand and result
       types.

       Note that while differences in memory organization are expected to largely be limited to
       those arising from endianness, the register based representation may also differ due to
       size of the element in register. (For example, an architecture may load a char into a
       32-bit register, or a char vector into a SIMD vector register with fixed 32-bit element
       size.)

       If the element count does not match, then the implementation should pick a data
       representation that most closely matches what would happen if an appropriate result type
       operator was applied to a register containing data of the source type. If the number of
       elements matches, then the as_typen() should faithfully reproduce the behavior expected
       from a similar data type reinterpretation using memory/unions. So, for example if an
       implementation stores all single precision data as double in register, it should implement
       as_int( float ) by first downconverting the double to single precision and then (if
       necessary) moving the single precision bits to a register suitable for operating on
       integer data.

       If data stored in different address spaces do not have the same endianness, then the
       "dominant endianness" of the device should prevail.

   Example
       float f = 1.0f; uint u = as_uint(f);  // Legal.
       Contains:  0x3f800000

       float4 f = (float4)(1.0f, 2.0f, 3.0f, 4.0f); //
       Legal. Contains: (int4) // (0x3f800000,
       0x40000000, 0x40400000, 0x40800000) int4 i =
       as_int4(f);

       float4 f, g; int4 is_less = f < g;

       // Legal. f[i] = f[i] < g[i] ? f[i] : 0.0f f =
       as_float4(as_int4(f) & is_less);

       int i; // Legal. Result is
       implementation-defined.  short2 j =
       as_short2(i);

       int4 i; // Legal. Result is
       implementation-defined.  short8 j =
       as_short8(i);

       float4 f; //Error. result and operand have
       different size double4 g = as_double4(f);   //
       Only if double is supported.

       float4 f; // Legal. g.xyz will have same values
       as f.xyz. g.w is undefined float3 g =
       as_float3(f);

SPECIFICATION

       OpenCL Specification[1]

SEE ALSO

       scalarDataTypes(3clc), vectorDataTypes(3clc)

AUTHORS

       The Khronos Group

COPYRIGHT

       Copyright © 2007-2011 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.

NOTES

        1. OpenCL Specification
           page 212, section 6.2.4.2 - Reinterpreting Types Using as_typen()