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;;; adler32.lisp -- computing adler32 checksums (rfc1950)
(in-package :chipz)
(defstruct (adler32
(:copier copy-adler32))
(s1 1 :type fixnum)
(s2 0 :type fixnum))
(defun update-adler32 (state vector start end)
(declare (type simple-octet-vector vector))
(declare (type index start end))
;; many thanks to Xach for his code from Salza.
(let ((length (- end start))
(i 0)
(k 0)
(s1 (adler32-s1 state))
(s2 (adler32-s2 state)))
(declare (type index i k length)
(type fixnum s1 s2))
(unless (zerop length)
(setf k (min 16 length))
(decf length k)
(setf s1 (+ (aref vector (+ start i)) s1))
(setf s2 (+ s1 s2))
(decf k)
(incf i)
(unless (zerop k)
(go sum))
(setf s1 (mod s1 adler32-modulo))
(setf s2 (mod s2 adler32-modulo))
(unless (zerop length)
(go loop))
(setf (adler32-s1 state) s1
(adler32-s2 state) s2)
(return-from update-adler32 state)))))
(defun produce-adler32 (state)
(logior (ash (adler32-s2 state) 16)
(adler32-s1 state)))