'\" t .\" Title: Reinterpreting Types Using as_type() and as_typen() .\" Author: The Khronos Group .\" Generator: DocBook XSL Stylesheets vsnapshot .\" Date: 01/14/2021 .\" Manual: OpenCL Manual .\" Source: The Khronos Group .\" Language: English .\" .TH "REINTERPRETING TYPES" "3clc" "01/14/2021" "The Khronos Group" "OpenCL Manual" .\" ----------------------------------------------------------------- .\" * Define some portability stuff .\" ----------------------------------------------------------------- .\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .\" http://bugs.debian.org/507673 .\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html .\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .ie \n(.g .ds Aq \(aq .el .ds Aq ' .\" ----------------------------------------------------------------- .\" * set default formatting .\" ----------------------------------------------------------------- .\" disable hyphenation .nh .\" disable justification (adjust text to left margin only) .ad l .\" ----------------------------------------------------------------- .\" * MAIN CONTENT STARTS HERE * .\" ----------------------------------------------------------------- .SH "NAME" Reinterpreting_Types_Using_as_type()_and_as_typen() .SS "" .TS tab(:); l l. T{ as_type() T} T{ as_type\fIn\fR() T} .TE .sp 1 .SH "DESCRIPTION" .PP All data types described in \fBscalarDataTypes\fR(3clc) and \fBvectorDataTypes\fR(3clc) (except \fBbool\fR, \fBhalf\fR (unless the \fBcl_khr_fp16\fR(3clc) extension is supported), and \fBvoid\fR) may be also reinterpreted as another data type of the same size using the \fBas_type()\fR operator for scalar data types and the \fBas_type\fR\fB\fIn\fR\fR\fB()\fR 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\&. .PP 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\&. .PP 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 \fBas_type()\fR or \fBas_type\fR\fB\fIn\fR\fR\fB()\fR operators to reinterpret data to a type of a different number of bytes\&. .SH "NOTES" .PP While the union is intended to reflect the organization of data in memory, the \fBas_type()\fR and \fBas_type\fR\fB\fIn\fR\fR\fB()\fR constructs are intended to reflect the organization of data in register\&. The \fBas_type()\fR and \fBas_type\fR\fB\fIn\fR\fR\fB()\fR 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\&. .PP 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\&.) .PP 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 \fBas_type\fR\fB\fIn\fR\fR\fB()\fR 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\&. .PP If data stored in different address spaces do not have the same endianness, then the "dominant endianness" of the device should prevail\&. .SS "Example" .TS tab(:); l. T{ 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); T} .TE .sp 1 .SH "SPECIFICATION" .PP \m[blue]\fBOpenCL Specification\fR\m[]\&\s-2\u[1]\d\s+2 .SH "SEE ALSO" .PP \fBscalarDataTypes\fR(3clc), \fBvectorDataTypes\fR(3clc) .SH "AUTHORS" .PP \fBThe Khronos Group\fR .SH "COPYRIGHT" .br Copyright \(co 2007-2011 The Khronos Group Inc. .br 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. .sp .SH "NOTES" .IP " 1." 4 OpenCL Specification .RS 4 \%page 212, section 6.2.4.2 - Reinterpreting Types Using as_typen() .RE