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Refactor uint Decoders

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Instead bit-shifting to 'place' the bits where we want them to be and
adding Lisp provides the DPB function that allows us to deposit bits
where we want them in an integer.
This commit is contained in:
Javier Olaechea 2019-03-24 16:43:20 -05:00
parent d130e45f58
commit 9facf444f4
1 changed files with 15 additions and 18 deletions
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33
osc.lisp
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@ -291,25 +291,22 @@
(ldb (byte 16 0) (decode-int32 s)))
#-(or sbcl cmucl openmcl allegro) (error "cant decode floats using this implementation"))
(defun decode-uint32 (s)
"4 byte -> 32 bit unsigned int"
(let ((i (+ (ash (elt s 0) 24)
(ash (elt s 1) 16)
(ash (elt s 2) 8)
(elt s 3))))
i))
(defmacro defint-decoder (num-of-octets &optional docstring)
(let ((decoder-name (intern (format nil "~:@(decode-uint~)~D" (* 8 num-of-octets))))
(seq (gensym))
(int (gensym)))
`(defun ,decoder-name (,seq)
,@(when docstring
(list docstring))
(let* ((,int 0)
,@(loop
for n below num-of-octets
collect `(,int (dpb (aref ,seq ,n) (byte 8 (* 8 (- (1- ,num-of-octets) ,n)))
,int))))
int))))
(defun decode-uint64 (s)
"8 byte -> 64 bit unsigned int"
(let ((i (+ (ash (elt s 0) 56)
(ash (elt s 1) 48)
(ash (elt s 2) 40)
(ash (elt s 3) 32)
(ash (elt s 4) 24)
(ash (elt s 5) 16)
(ash (elt s 6) 8)
(elt s 7))))
i))
(defint-decoder 4 "4 byte -> 32 bit unsigned int")
(defint-decoder 8 "8 byte -> 64 bit unsigned int")
(defmacro defint-encoder (num-of-octets &optional docstring)
(let ((enc-name (intern (format nil "~:@(encode-int~)~D" (* 8 num-of-octets))))