Refactor int Encoders
Instead of Shifting bits and masking in order to extract a subset of the bits Lisp provides the function LBD, which allows us to extract a number of bits from an integer. This approach is more direct, communicates the intent better and allows the compiler to do less work.
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1 changed files with 16 additions and 31 deletions
47
osc.lisp
47
osc.lisp
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@ -352,20 +352,6 @@ with the current time use (encode-timetag :time)."
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(ldb (byte 16 0) (decode-int32 s)))
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#-(or sbcl cmucl openmcl allegro) (error "cant decode floats using this implementation"))
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(defun encode-int32 (i)
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"convert an integer into a sequence of 4 bytes in network byte order."
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(declare (type integer i))
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(let ((buf (make-sequence
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'(vector (unsigned-byte 8)) 4)))
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(macrolet ((set-byte (n)
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`(setf (elt buf ,n)
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(logand #xff (ash i ,(* 8 (- n 3)))))))
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(set-byte 0)
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(set-byte 1)
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(set-byte 2)
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(set-byte 3))
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buf))
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(defun decode-int32 (s)
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"4 byte -> 32 bit int -> two's compliment (in network byte order)"
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(let ((i (+ (ash (elt s 0) 24)
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@ -384,24 +370,23 @@ with the current time use (encode-timetag :time)."
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(elt s 3))))
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i))
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(defmacro defint-encoder (num-of-octets &optional docstring)
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(let ((enc-name (intern (format nil "~:@(encode-int~)~D" (* 8 num-of-octets))))
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(buf (gensym))
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(int (gensym)))
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`(defun ,enc-name (,int)
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,@(when docstring
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(list docstring))
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(let ((,buf (make-array ,num-of-octets :element-type '(unsigned-byte 8))))
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,@(loop
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for n below num-of-octets
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collect `(setf (aref ,buf ,n)
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(ldb (byte 8 (* 8 (- (1- ,num-of-octets) ,n)))
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,int)))
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,buf))))
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(defun encode-int64 (i)
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"convert an integer into a sequence of 8 bytes in network byte order."
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(declare (type integer i))
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(let ((buf (make-sequence
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'(vector (unsigned-byte 8)) 8)))
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(macrolet ((set-byte (n)
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`(setf (elt buf ,n)
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(logand #xff (ash i ,(* 8 (- n 7)))))))
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(set-byte 0)
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(set-byte 1)
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(set-byte 2)
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(set-byte 3)
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(set-byte 4)
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(set-byte 5)
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(set-byte 6)
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(set-byte 7))
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buf))
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(defint-encoder 4 "Convert an integer into a sequence of 4 bytes in network byte order.")
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(defint-encoder 8 "Convert an integer into a sequence of 8 bytes in network byte order.")
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(defun decode-uint64 (s)
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"8 byte -> 64 bit unsigned int"
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