6502-OS/util/parity.h65

.ifndef INCLUDE_PARITY
INCLUDE_PARITY = 1

;;********************************************************************************
;; @file
;; @brief Macros for calculating parity
;; @ingroup libs
;;********************************************************************************

.import count_set_bits

;;********************************************************************************
;; @macro Calculate even parity
;; @modifies A, X, Y
;; @returns A: 0 - even number of set bits, 1 - uneven number of set bits
;; @returns Y: The number of set bits in the byte
;;********************************************************************************
.macro CalculateEvenParity
    jsr count_set_bits
    tya
    and #1
.endmacro


;;********************************************************************************
;; @macro Calculate odd parity
;; @details
;;  Count the number of set bits in Y.
;;  
;; @modifies A, X, Y
;; @returns A: 1 - even number of set bits, 0 - uneven number of set bits
;; @returns Y: The number of set bits in the byte
;;********************************************************************************
.macro CalculateOddParity
    jsr count_set_bits
    tya
    and #1
    eor #1
.endmacro

.endif  ; guard