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Fix #283: Add VOP for integer-length for an (unsigned-byte 32) arg

Raymond Toy requested to merge issue-283-unsigned-integer-length-vop into master

There's a VOP for integer-length for (signed-byte 32) arg, but not one for (unsigned-byte 32). We can use the BSR instruction to handle this case.

Not sure exactly how to test this, but I did it manually by compiling

(defun zot-u (n)
  (declare (type (unsigned-byte 32) n)
           (optimize (speed 3)))
  (integer-length n))

The disassembly is, in part

CL-USER> (disassemble 'zot-u)
604ad710:       .entry zot-u(n)                        ; (function
...
      70: L5:   cmp       edx, #x0                     ; No-arg-parsing entry point
                                                       ; [:non-local-entry]
      73:       je        L6
      75:       bsr       edx, edx
      78:       inc       edx
      79:       shl       edx, #x2

Without this VOP, the disassembly would be

     228: L3:   mov       eax, dword ptr [#x609c31d4]  ; #<FDEFINITION object for integer-length>
                                                       ; No-arg-parsing entry point
                                                       ; [:non-local-entry]
     22e:       mov       ecx, #x4
     233:       push      dword ptr [ebp-#x8]

;;; [9] (INTEGER-LENGTH N)

     236:       jmp       dword ptr [eax+#x5]          ; [:call-site]

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