opencl

read_imagef，

float4 read_imagef (　image2d_t image,
      　　　　　　　　sampler_t sampler,
      　　　　　　　　int2 coord)
Description:
Use the coordinate (x, y) to do an element lookup in the 1D or 2D image object specified by image.

opencl has 4 data type categories:

1 scalar, 2 vector, 3 abstract, 4 reserved, and other data type

among vector data types, intn means a vector of n 32-bit signed two's complement integer values.

mad
Approximates a * b + c. 

gentype mad (     gentype a,
      gentype b,
      gentype c)

Description
mad approximates a * b + c. Whether or how the product of a * b is rounded and how supernormal or subnormal intermediate products are handled is not defined. mad is intended to be used where speed is preferred over accuracy.