PPT 슬라이드
To accomplish arithmetic operations on arrays --in effect treating them as binary or numerical representations, requires functions (sub-programs) supplied by the IEEE or the tool vendor.
The package std_logic_unsigned is an IEEE standard library and will provide maximum code portability.
Such functions will normally be included in so-called “arithmetic packages”. The package may require compilation into the work library. FPGA Express has pre-compiled these packages into its own internal library.
package std_logic_unsigned is function “+” (A,B: bit_vector) return bit_vector ; function “+” (A: bit_vector, B: integer ) return bit_vector ; function “-” (A,B: bit_vector) return bit_vector ; . . . .
library IEEE ; use IEEE.std_logic_1164.all ; use IEEE.std_logic_unsigned.all ;
The operator “+” is overloaded in that it refers to a different function call, based on the left and right operand, and the return parameter in the function declaration.