CRC routines.

Computes CRC-16 (CCITT).

Description

This function updates the current CRC-16 with the value of the A register.  The current implementation is based on Greg Cook CRC-16.

For more informations

• https://en.wikipedia.org/wiki/Computation_of_cyclic_redundancy_checks
• http://www.6502.org/source/integers/crc-more.html

Assembly call

; reset CRC-16 value
stwz   <_crc

; _si contains the address of the input buffer
; X contains its size
cly
loop:
    phy
    phx

    lda    [_si], Y
    jsr    crc16

    plx
    ply
    iny
    dex
    bne    loop
; at the end of the loop _crc contains the 16 bit CRC of the input buffer

Parameters

Return

Resets CRC-32 value.

Return

Computes CRC-32.

Description

This function updates the current CRC-32 with the value of the A register.  The following implementation is based on Kevin Horton CRC32 checksum code.

For more informations

• https://en.wikipedia.org/wiki/Computation_of_cyclic_redundancy_checks
• https://wiki.nesdev.com/w/index.php/Calculate_CRC32

Assembly call

; reset CRC-32 value
jsr    crc32_begin

; _si contains the address of the input buffer
; X contains its size
cly
loop:
    phy
    phx

    lda    [_si], Y
    jsr    crc32

    plx
    ply
    iny
    dex
    bne    loop

; finalize CRC-32 computation
jsr    crc32_end

Parameters

Return

Finalizes CRC-32 value.

Return