I don't use gnu awk, and the awk I use doesn't have strtonum() as a built-in; but I don't see how this is going to work. Since j starts with a default value of 0, the 2nd time through the loop for the 1st input line is going to reset the end of the loop value initially presented as input $2 value. And, since j isn't reset between lines, subsequent output lines will copy the start and end points as the first two output fields in the output , followed by a number of empty fields that varies depending on how many fields have been output on the previous lines, followed by the desired output. If you want to do this using awk instead of ksh, it would seem that the following might work better:

Code:

awk -F: '
{	h=("0x"$2)+0
	j=0
	for (i = ("0x"$1) + 0; i <= h; i++)
		$(++j) = sprintf("%X", i)
}
1' OFS=, infile

Note that I used %X instead of %x in the sprintf() format string because the submitter seems to want uppercase hex digits instead of lowercase.
As always, if you want to try this on a Solaris/SunOS system, change awk to /usr/xpg4/bin/awk or nawk.