cvhi4(input_buffer.i1a.r, start_index.i2.r, num_chars.i2.r, value.i4.r,

	This routine will convert the number of hexadecimal characters
	specified by "num_chars" from the user's byte buffer, "input_buffer",
	to an value in "value".  The conversion starts at the character
	position specified by "start_index" (first character is position 1).
	If a null character is encountered, the conversion will be terminated.
	If a valid conversion has been performed, the value of "error" is
	returned as zero.  Otherwise, the position of the first 'bad'
	character is returned in "error" as a negative value.