The half data type must be IEEE 754-2008 compliant. half numbers have 1 sign bit, 5 exponent bits, and 10 mantissa bits. The interpretation of the sign, exponent and mantissa is analogous to IEEE 754 floating-point numbers. The exponent bias is 15. The half data type must represent finite and normal numbers, denormalized numbers, infinities and NaN. Denormalized numbers for the half data type which may be generated when converting a float to a half using vstore_half and converting a half to a float using vload_half cannot be flushed to zero. Conversions from float to half correctly round the mantissa to 11 bits of precision. Conversions from half to float are lossless; all half numbers are exactly representable as float values.

The half data type can only be used to declare a pointer to a buffer that contains half values. A few valid examples are given below:

bar (__global half *p)

__kernel void
foo (__global half *pg, __local half *pl)
    __global half *ptr;
    int offset;

    ptr = pg + offset;

Below are some examples that are not valid usage of the half type:

half a;
half b[100];
half *p;
a = *p; //  not allowed. must use *vload_half* function

Loads from a pointer to a half and stores to a pointer to a half can be performed using the vector data load and store functions vload_half, vload_halfn, vloada_halfn and vstore_half, vstore_halfn, and vstorea_halfn. The load functions read scalar or vector half values from memory and convert them to a scalar or vector float value. The store functions take a scalar or vector float value as input, convert it to a half scalar or vector value (with appropriate rounding mode) and write the half scalar or vector value to memory.

See Also

Document Notes

For more information, see the OpenCL C Specification

This page is extracted from the OpenCL C Specification. Fixes and changes should be made to the Specification, not directly.

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