Stream User’s Guide
Download 0.95 Mb.
|
- Navigate this page:
- ==, !=, , = relations
6.5OperatorsExpressions within a kernel function can use many standard C operators. Some operators map to a single DPU intrinsic operation; the Intrinsic operations section below gives an overview of intrinsics, and the Stream Reference Manual gives a detailed description of each intrinsic. For example: vec int16x2 a, b, x; x = a + b; // equivalent to x = spi_vadd16i(a, b); This does just what the programmer expects: it performs two signed 16-bit additions in each lane (one in each halfword of each lane). Because of its SIMD architecture, the DPU performs computations in each lane simultaneously, and therefore the value of a vector expression differs in each lane. This operation requires only a single intrinsic. Some operators map to multiple intrinsics. For example, the DPU does not support 32-bit by 32-bit multiplication: vec int32x1 a, b, x; x = a * b; // requires multiple DPU operations This generates multiple operations to perform the required multiplication. Similarly, DPU intrinsics for relational operators return all 0 bits or all 1 bits rather than the C relational values of 0 or 1, so vec int16x2 a, b, x; x = (a != b); // requires multiple DPU operations generates multiple operations rather than simply calling intrinsic spi_vne16. See section DPU booleans above for additional information about relational operators and DPU boolean intrinsics. Kernel functions may not use all C operators. The Kernel intrinsic functions section of the Stream Reference Manual contains additional details about each operator, including argument type information. Supported operators in kernel expressions include:
In kernel expressions, the ‘&&’ and ‘||’ operators do not use the C evaluation “short circuit” rules; the second argument is always evaluated, regardless of the value of the first argument. Similarly, ternary operator ‘?:’ does not use the C evaluation “short circuit” rule; both the second and third arguments are always evaluated, regardless of the value of the first argument. If ‘?:’ arguments contain side effects (e.g., assignments), the result is undefined. Some C operators are not supported within kernel functions. These include:
Download 0.95 Mb. Share with your friends:
|