expp (Vertex Shader)

Provides partial precision exponential 2^x.

Syntax

where

• dst is the destination register.
• src is a source register. Source register requires explicit use of replicate swizzle, that is, exactly one of the .x, .y, .z, .w swizzle components (or the .r, .g, .b, .a equivalents) must be specified.

Remarks

The following code fragment shows the operations performed.

float w = src.w;
float v = (float)floor(src.w);
dest.x = (float)pow(2, v);
dest.y = w - v;

// Reduced precision exponent
float tmp = (float)pow(2, w);
DWORD tmpd = *(DWORD*)&tmp & 0xffffff00;
dest.z = *(float*)&tmpd;
dest.w = 1;

This instruction provides exponential base 2 partial precision. It allows for a more accurate determination of dest.x*function(dest.y), where function is a user approximation to 2*dest.y over the limited range where dest.y is between 0.0 and 1.0.

This instruction provides 10-bit precision.

Instruction Information