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bin/50959: /bin/sh does not support 0Xxxx literal constants in $(( )) evaluation

>Number:         50959
>Category:       bin
>Synopsis:       /bin/sh does not support 0Xxxx literal constants in $(( )) evaluation
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    bin-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Mar 12 18:15:00 +0000 2016
>Originator:     Robert Elz
>Release:        NetBSD 7.99.26 (anything to date of this PR)
System: NetBSD 7.99.26 NetBSD 7.99.26 (VBOX64-1.1-20160128) #43: Thu Jan 28 16:09:08 ICT 2016 amd64
Architecture: x86_64
Machine: amd64
	$(( )) expressions are required to allow decimal, hex, and
	octal constants (as operands of the expression - the result
	is always decimal.)

	NetBSD's /bin/sh does all of that, provided that the hex constant
	form uses a lower case 'x' in the leading 0x, rather than upper
	case 'X'.

	Further, if the hex constant is assigned to a variable, and the
	variable name is used in an expression, then hex constants work
	regardless of whether it is 0x or 0X.   Not very consistent.

		/bin/sh -c 'echo $(( 0x1 )); echo $(( 0X1 ))' 2>&1
		sh: arith: syntax error: " 0X1 "

		/bin/sh -c 'V=0x1; W=0X1; echo $(( V )) $(( W ))'
		1 1

		/bin/sh -c 'V=0x1; W=0X1; echo $(( $V )) $(( $W ))'
		sh: arith: syntax error: " 0X1 "

	Note that in the second, V and W have string values, they are
	only converted to integers when used inside $(()).  The third
	example illustrates that (there's no output in that case as
	the whole echo command fails when the syntax error is detected,
	but the $V expression would be just fine).   This case is just
	the same thing as the first of course.

	Trivial to fix...   already done in my copy, this is another of the
	/bin/sh placeholder PRs just to reference when the fix is committed.

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