std_logic_arithThis is the library that defines some types and basic arithmetic operations for representing integers in standard ways. This is a Synopsys extention. The source code is in std_logic_arith.vhd and is freely redistributable.
unsigned type
  signed type
  +, -, *
  <, <=, >, >=, =, /=
  shl, shr
  conv_integer function
  conv_unsigned function
  conv_signed function
  conv_std_logic_vector function