Introduction to the High-Level Shading Language - Introduction to 3D Game Programming with DirectX 9.0 - page 285

will be shared across multiple effects. Only global variables can be
prefixed with the shared keyword.
volatile —If a variable is prefixed with the volatile keyword,
it hints to the effects framework (see Chapter 19) that the variable
will be modified often. Only global variables can be prefixed with
the volatile keyword.

const —The const keyword in HLSL has the same meaning it
has in C++. That is, if a variable is prefixed with the const key-
word, then that variable is constant and cannot be changed.
const float pi = 3.14f;

16.4 Keywords, Statements, and Casting

16.4.1 Keywords
For reference, here is a list of the keywords that HLSL defines:

asm bool compile const decl do

double else extern false float for

half if in inline inout int

matrix out pass pixelshader return sampler

shared static string struct technique texture

true typedef uniform vector vertexshader void

volatile while

This next set displays identifiers that are reserved and unused but may
become keywords in the future:

auto break case catch char class

const_cast continue default delete dynamic_cast enum

explicit friend goto long mutable namespace

new operator private protected public register

reinterpret_cast short signed sizeof static_cast switch

template this throw try typename union

unsigned using virtual

16.4.2 Basic Program Flow
HLSL supports many familiar C++ statements for selection, repeti-
tion, and general program flow. The syntax of these statements is
exactly like C++.