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+# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
+
+include	<ctype.h>
+include	<printf.h>
+
+.help
+.nf _________________________________________________________________________
+Process a format descriptor, setting the variables "decpl", "fill_char",
+"format_char", and "width" in the fmtio common.  Called from PARG_
+to determine the format specification for printing a variable.
+
+Format: "%[w[.d]]C[n]", where W is the field width, D the number of decimal
+places or precision, C the format type character, and N the radix numeral,
+for format type FMT_RADIX only.  A negative field width signifies left
+justification.  A leading zero in the W field sets the fill character to the
+numeral zero (when right justifying).  Default values will be supplied if
+any of the fields are omitted.  The minimum format is "%C".
+
+If any of the fields (wdCn) have the value GET_FIELD (= "*") the value of
+the field will be taken from the next PARG_ call, rather than from the
+format string.  This makes it easy to vary the format specification at run
+time.  For example, "%10.*g" would print a number in G-floating format,
+with a constant field width of 10, and with the number of digits of precision
+being given by a PARGI call at execution time (followed by a PARG_ call to
+pass the value to be printed).
+.endhelp ____________________________________________________________________
+
+# The following macro marks the position in the FPRFMT procedure (saves the
+# code for the needed field), and returns the not done status to PARG_.
+# A subsequent call to a PARG_ (with the value of the field we are waiting for
+# as argument) causes FPRFMT to be reentered at the point where we left off.
+
+define	(waitfor,	if (ival_already_used) { fmt_state = $1; return (NOT_DONE_YET) } ; $1 ival_already_used = true)
+
+#define	(waitfor,	if (ival_already_used) {
+#			    fmt_state = $1
+#			    return (NOT_DONE_YET)
+#			}
+#			$1 ival_already_used = true)
+
+# FPRFMT -- Process a %W.Dn format specification.  ALL_DONE is returned when
+# the format specification has been fully processed, else NOT_DONE_YET is
+# returned, indicating that an additional PARG call is required to complete
+# the format (which therefore contained one or more "*" specifiers).
+
+int procedure fprfmt (ival)
+
+int	ival					# argument value (from parg_)
+bool	ival_already_used			# wait for next parg
+int	ctoi(), stridx()
+char	ch, chrlwr()
+include "fmt.com"
+
+begin
+	# This routine functions as a coroutine.  If one of the fields in
+	# the format spec is to be given in a pargi call, an early return
+	# is taken.  The routine is later reentered with the value of the
+	# needed field, and execution continues at the point it left off.
+	# (Sorry, I could not think of a simpler way to do it...)
+
+	switch (fmt_state) {				# return from "waitfor"
+	case FMT_START:					# initial state
+	    ival_already_used = false
+	case GET_WIDTH_1:				# "%*.dC"
+	    goto GET_WIDTH_1
+	case GET_WIDTH_2:				# "%-0*.dC"
+	    goto GET_WIDTH_2
+	case GET_DECPL:					# "%w.*C"
+	    goto GET_DECPL
+	case GET_FMTCHAR:				# "%w.d*"
+	    goto GET_FMTCHAR
+	case GET_RADIX:					# "%w.dr*"
+	    goto GET_RADIX
+	case GET_OPERAND:				# used ival for format
+	    goto GET_OPERAND
+	}
+	
+	# It is not an error if there is no format string.
+	if (format[ip] == EOS || format[ip] != START_OF_FORMAT) {
+	    width = USE_DEFAULT
+	    decpl = USE_DEFAULT
+	    format_char = USE_DEFAULT
+	    fill_char = ' '
+	    left_justify = NO
+	    fmt_state = FMT_START
+	    return (ALL_DONE)
+	} else
+	    ip = ip + 1					# eat the "%"
+	    
+	if (format[ip] == GET_FIELD) {			# "%*.dC"
+	    ip = ip + 1
+	    waitfor (GET_WIDTH_1)			# go get field width...
+	    if (ival < 0)				# ...and come back here
+		left_justify = YES
+	    else
+		left_justify = NO
+
+	    fill_char = ' '
+	    width = abs (ival)
+
+	} else {					# "%-0*.dC"
+	    if (format[ip] == '-') {			# left or right justify
+		left_justify = YES
+		ip = ip + 1
+	    } else
+		left_justify = NO
+
+	    fill_char = ' '				# zero or blank fill
+	    if (format[ip] == '0') {
+		if (IS_DIGIT (format[ip+1]) || format[ip+1] == GET_FIELD) {
+		    fill_char = '0'
+		    ip = ip + 1
+		} else
+		    fill_char = ' '
+	    }
+
+	    if (format[ip] == GET_FIELD) {
+		ip = ip + 1
+		waitfor (GET_WIDTH_2)			# go get field width...
+		if (ival < 0)				# ... and come back here
+		    left_justify = YES
+		else
+		    left_justify = NO
+		width = abs (ival)
+
+	    } else if (ctoi (format, ip, width) <= 0)	# "%N.dC"
+		width = USE_DEFAULT
+	}
+
+	if (width == 0)					# make as big as needed
+	    width = USE_DEFAULT
+
+	if (format[ip] == '.') {			# get decpl field
+	    ip = ip + 1
+	    if (format[ip] == GET_FIELD) {		# "%w.*C"
+		ip = ip + 1
+		waitfor (GET_DECPL)
+		decpl = ival
+	    } else if (ctoi (format, ip, decpl) <= 0)	# "%w.NC"
+		decpl = USE_DEFAULT
+	} else
+	    decpl = USE_DEFAULT
+
+	if (format[ip] == GET_FIELD) {			# "%w.d*"
+	    ip = ip + 1
+	    waitfor (GET_FMTCHAR)
+	    format_char = ival
+	} else {
+	    format_char = format[ip]			# "%w.dC"
+	    ip = ip + 1
+	}
+
+	ch = format_char
+	if (stridx (ch, "bcdefghHmMorstuwxz") <= 0) {
+	    call putline (STDERR, "Warning: Unknown format type char\n")
+	    call fmt_err ("", format, ip-1)
+	    format_char = USE_DEFAULT
+
+	} else if (format_char == FMT_RADIX) {		# get radix
+	    ch = chrlwr (format[ip])
+	    ip = ip + 1
+	    if (ch == GET_FIELD) {			# "%w.dr*"
+		waitfor (GET_RADIX)
+		radix = ival
+	    } else if (IS_DIGIT (ch)) {
+		radix = TO_INTEG (ch)
+	    } else if (IS_LOWER (ch)) {
+		radix = ch - 'a' + 10
+	    } else {
+		radix = DECIMAL
+		ip = ip - 1
+	    }
+
+	} else if (format_char == FMT_WHITESPACE || format_char == FMT_TOCOLUMN)
+	    ival_already_used = false			# no operand
+
+	waitfor (GET_OPERAND)				# used ival for format,
+	fmt_state = FMT_START				# need to get another
+	return (ALL_DONE)
+end