upgraded-array-element-type/class-of for arrays

[mevenson]

Alan notes in <​https://github.com/armedbear/abcl/issues/84>

No code of mine depends on this, but I was reading an article and it prompted me to check types of arrays and how upgraded-array-element-type works.

Bottom line is that it isn't consistent.

CL-USER> (make-array 1 :element-type '(unsigned-byte 16))
#(0)
CL-USER> (jobject-class *)
#<java class org.armedbear.lisp.BasicVector_UnsignedByte16 {6F28B4E2}>
CL-USER> (class-of (make-array 1 :element-type '(unsigned-byte 16)))
#<built-in-class vector {352D86C9}>
CL-USER> (upgraded-array-element-type '(unsigned-byte 16))
(unsigned-byte 16)
CL-USER> (make-array 1 :element-type '(unsigned-byte 17))
#(0)
CL-USER> (jobject-class *)
#<java class org.armedbear.lisp.BasicVector_UnsignedByte32 {1C49E33C}>
CL-USER> (upgraded-array-element-type '(unsigned-byte 17))
t
CL-USER> (class-of (make-array 1 :element-type '(unsigned-byte 17)))
#<built-in-class vector {352D86C9}>

Summary:

    Implementation of arrays of unsigned byte 16 vs 17 are different
    class-of reports the same type
    upgraded-array-element-type of (unsigned-byte 17) reports t, but it is in fact (unsigned-byte 32)
    trying to set array element of (unsigned-byte 17) to int larger than 2^17 works, but not setting to a symbol, as type t would imply