#!/usr/bin/env bash

# SCRIPT TO COMPUTE OR PLOT US FEDERAL TAX RATES, TAX YEARS 1987 - 2012
# Last update:  Dec 31, 2011
#
# Usage:  (run with no arguments for an explanation)
#
# NO WARRANTY ON THIS DATA.  USE AT YOUR OWN RISK.
#
# I suggest you use this for estimates only, such as with a spreadsheet, and
# refer to IRS tables for actual values.  (If you ever detect a discrepancy,
# however, please let me know.)  The formulas used for 1988 and later years are
# explained below.
#
# WARNING:  Doesn't know that 1991-2012 long term capital gains, or later
# qualified dividends, are taxed at a reduced rate (depending on your tax
# bracket).  This can result in an overestimate of tax due.
#
# WARNING:  Doesn't plot correctly if asked (via $maxti, see below) to plot
# rates for 1988-1990 above C3 (see below) for any tax status, but it gives
# warnings if this applies.  Above C3 the curves branch into families depending
# on number of exemptions.  This doesn't apply to very many people.
#
# See below for explanations of the algorithms.
#
# Below $100000 taxable income ($50000 before 1993 (?)), you have to use the
# tax tables, which are quantized into $50 steps (or $25 steps below $3000,
# ignores smaller steps in $0-25 range).  The tax computation understands this
# (I hope), but the plot doesn't show this detail.


# AMOUNT OF WITHHOLDING REQUIRED (as of 9606):
#
# You must make quarterly estimated tax payments if:
#
#	tax - (withholding + credits) >= $500
# AND	(withholding + credits) < MIN (prev_year_tax, 0.9 * curr_year_tax)


# EXPLANATION OF RATES FOR 1988 - 1990:
#
# Variables:
#
#	T   taxable income (total income less all adjustments and deductions)
#	E   number of exemptions
#	t   tax due
#
# Tax formula:
#
#	t = 0.15 * T				(a) 15%, lowest bracket.
#	  + 0.13 * (max (0, T - C1))		(b) 28%, next bracket.
#	  + 0.05 * (  max (0, T - C2)		(c) 33%, Rate Adjustment brkt.
#		    - max (0, T - C3)		(d) 28%-of-total bracket.
#		    + min ((E * K),		(e) Phaseout of Personal
#			   max (0, T - C3)))	(f)   Exemptions adjustment.
#
# C1, C2, C3, and K values vary for each year.  They are listed in the tables
# below.
#
# When (T >= C3), part (d) comes in to cancel part (c) except for 5% of (C3 -
# C2), so the rate reverts to 28%.  But now it applies all of T, not just the
# amount above C1.  In other words, the amount saved in the 15% lowest bracket
# is added back in:
#
#		0.13 * C1 = 0.05 * (C3 - C2)
#
# Working through the math for (T >= C3), parts (a) through (d) collapse:
#
#		t = 0.15 * T
#		  + 0.13 * (T - C1)
#		  + 0.05 * (T - C2 - T + C3)
#
#		  = 0.28 * T
#		  - 0.13 * C1
#		  + 0.05 * (C3 - C2)
#
#		  = 0.28 * T
#
# There's one exception.  Status ms (married, single) is structured so 5% of
# (C3 - C2) is twice 13% of C1.  Apparently there is a discontinuity.  People
# just below C3 pay almost $2000 more tax than those just above it, because the
# latter pay a flat 28% (unless the Phaseout of Personal Exemption applies).
# There's a note in the 1989 worksheet that might counteract this; I'm not
# sure.
#
# The Phaseout of Personal Exemptions may delay the reversion to 28% (of all of
# T) until higher income levels, depending on your exemptions.  Part (f) tries
# to add back the extra 5%, but can only do so if less than part (e).  This
# creates a family of curves above C3 for each filing status.


# EXPLANATION OF RATES FOR 1991 - 2012:
#
# They apparently lowered the top tax rate and got rid of the Phaseout of
# Personal Exemptions.  So the formula is similar to but simpler than that
# above, more like the 1987 formula, but with even fewer brackets (until the
# 1993 tax act retroactively added more brackets, sigh).
#
# Variables:
#
#	T   taxable income (total income less all adjustments and deductions)
#	t   tax due
#
# Tax formula:
#
#	t = 0.15  * T				(a) 15%, lowest bracket.
#	  + 0.13  * (max (0, T - C1))		(b) 28%, next bracket.
#	  + 0.03  * (max (0, T - C2))		(c) 31%, top bracket.
# 1993 and later:
#	  + 0.05  * (max (0, T - C3))		(d) 36%, next bracket.
#	  + 0.036 * (max (0, T - C4))		(e) 39.6%, top bracket.
#
# 2001 and later, brackets change and a new 10% bracket is added starting in
# 2002.  For 2001 the same effect is provided by a rebate and using the old 15%
# base rate; nope, the tax rate schedules in the 2001 workbook are actually as
# shown below, probably because the rebate was all-year but the new tax rates
# were half-year?
#
#	2001	2002
#	.	10%
#	15%	15%
#	27.5%	27%
#	30.5%	30%
#	35.5%	35%
#	39.1%	38.6%
#
# 030604:  Tax law just passed apparently puts 2006 rates in place for 2004.


# INITIALIZE:

	spool=''
	device=''		# use defaults in program (or $PLOTDEV).
	driver=''

# alternate options:
#	spool=''
#	device='-d/dev/tty'
#	driver='-rhp2623'

#	spool='-sa'
#	device="-d$PWD/temp"
#	driver='-rhpgl'

	maxti='50000'		# default right sides (max X values) of plots.

	plotdir='/var/tmp/taxplotdata'		# holds files to plot.


# CHECK INVOCATION:

	if [[ ($# != 1) && ($# != 2) && ($# != 3) && ($# != 4) ]]  # wrong args.
	then
	    # This is an interpreted here-doc:

	    cat >&2 <<-!
usage:  $0 year [year2 | status taxable-income [exemptions]]

Year must be 87..99 or 00..12.
Status must be s, mj, ms, or hh.
Taxable-income is the net dollar figure after all adjustments, exemptions,
and deductions.

Given only a year (or two), does a rates plot to device $device using
driver "$driver".  (The device and driver are hardwired into the script
or set with \$PLOTDEV.)

With additional arguments, computes and prints the tax (in dollars) for the
given year, status, and taxable-income.  For example:

    $0 91 mj 45319

Exemptions (default: 0) are ignored except for high incomes for 1988-1990.
		!

	    exit 1
	fi


# CHECK ARGUMENTS:

	case "x$1" in

	x87 | x88 | x89 | \
	x90 | x91 | x92 | x93 | x94 | x95 | x96 | x97 | x98 | x99 | \
	x00 | x01 | x02 | x03 | x04 | x05 | x06 | x07 | x08 | x09 | \
	x10 | x11 | x12 )  ;;

	* )  echo "$0:  year must be 87..99 or 00..12" >&2
	     exit 1 ;;
	esac

	if [[ (${1#0} -ge 87) && (${1#0} -lt 93) ]]	# old range.
	then table='50000'
	else table='100000'
	fi

	if [[ $# -ge 3 ]]		# need to check status, etc.
	then
	    case "x$2" in
	    xs | xmj | xms | xhh )  ;;
	    *)	echo "$0:  status must be s, mj, ms, or hh" >&2
		exit 1 ;;
	    esac

# Modify taxable income ($3) to center of bracket in which it falls:
# Also set exemptions to 0 if not specified.

	    set -- "$1" "$2" `awk < /dev/null 'END {
		if	('"$3"' <     5)  print  0;
		else if	('"$3"' <    15)  print 10;
		else if	('"$3"' <    25)  print 20;
		else if	('"$3"' <  3000)  print (int ('"$3"' / 25) * 25) + 12.5;
		else if	('"$3"' < '$table') print (int ('"$3"' / 50) * 50) + 25;
		else			  print '"$3"';
	    }'` "${4:-0}"
	fi

# CONSTANTS FOR 1987 (based on 1040 tax rate schedules):

	case $1 in

	87 )
	    # Constants are tops of 11%, 15%, 28%, and 35% brackets.
	    # Above that is 38.5%.
	    #
	    #	status	C1	C2	C3	C4

	    cat <<-'!'
		s	1800	16800	27000	54000
		mj	3000	28000	45000	90000
		ms	1500	14000	22500	45000
		hh	2500	23000	38000	80000
		!
	    ;;

# CONSTANTS FOR 1988 (based on 1988 1040ES):

	88 )
	    # Constants are tops of 15%, 28%, and 33% brackets.
	    # Above that it gets complicated.  See explanation above.
	    #
	    #	status	C1	C2	C3	K

	    cat <<-'!'
		s	17850	43150	 89560	10920
		mj	29750	71900	149250	10920
		ms	14875	35950	113300	10920
		hh	23900	61650	123790	10920
		!
	    ;;

# CONSTANTS FOR 1989 (based on 1989 1040 workbook, page 41):

	89 )
	    # Constants are tops of 15%, 28%, and 33% brackets.
	    # Above that it gets complicated.  See explanation above.
	    #
	    #	status	C1	C2	C3	K

	    cat <<-'!'
		s	18550	44900	 93130	11200
		mj	30950	74850	155320	11200
		ms	15475	37425	117895	11200
		hh	24850	64200	128810	11200
		!
	    ;;

# CONSTANTS FOR 1990 (based on 1990 1040ES):

	90 )
	    # Constants are tops of 15%, 28%, and 33% brackets.
	    # Above that it gets complicated.  See explanation above.
	    #
	    #	status	C1	C2	C3	K

	    cat <<-'!'
		s	19450	47050	 97620	11480
		mj	32450	78400	162770	11480
		ms	16225	39200	123570	11480
		hh	26050	67200	134930	11480
		!
	    ;;

# CONSTANTS FOR 1991 (based on 1991 1040ES):

	91 )
	    # Constants are tops of 15% and 28% brackets.  Above that is 31%.
	    #
	    #	status	C1	C2

	    cat <<-'!'
		s	20350	49300
		mj	34000	82150
		ms	17000	41075
		hh	27300	70450
		!
	    ;;

# CONSTANTS FOR 1992 (based on 1992 1040ES) (each exemption = $2300):

	92 )
	    # Constants are tops of 15% and 28% brackets.  Above that is 31%.
	    #
	    #	status	C1	C2

	    cat <<-'!'
		s	21450	51900
		mj	35800	86500
		ms	17900	43250
		hh	28750	74150
		!
	    ;;

# CONSTANTS FOR 1993 (based on 1993 1040) (each exemption = $2350):

	93 )
	    # Constants are tops of 15%, 28%, 31%, and 36% brackets.  Above
	    # that is 39.6%.
	    #
	    #	status	C1	C2	C3	C4

	    cat <<-'!'
		s	22100	53500	115000	250000
		mj	36900	89150	140000	250000
		ms	18450	44575	 70000	125000
		hh	29600	76400	127500	250000
		!
	    ;;

# CONSTANTS FOR 1994 (based on 1994 1040 Pub 919) (each exemption = $2450):

	94 )
	    # Constants are tops of 15%, 28%, 31%, and 36% brackets.  Above
	    # that is 39.6%.  Note, C3 and C4 are unchanged from 1993.
	    #
	    #	status	C1	C2	C3	C4

	    cat <<-'!'
		s	22750	55100	115000	250000
		mj	38000	91850	140000	250000
		ms	19000	45925	 70000	125000
		hh	30500	78700	127500	250000
		!
	    ;;

# CONSTANTS FOR 1995 (based on 1995 1040ES) (each exemption = $2500):

	95 )
	    # Constants are tops of 15%, 28%, 31%, and 36% brackets.  Above
	    # that is 39.6%.
	    #
	    #	status	C1	C2	C3	C4

	    cat <<-'!'
		s	23350	56550	117950	256500
		mj	39000	94250	143600	256500
		ms	19500	47125	 71800	128250
		hh	31250	80750	130800	256500
		!
	    ;;

# CONSTANTS FOR 1996 (based on 1996 1040ES) (each exemption = $2550):

	96 )
	    # Constants are tops of 15%, 28%, 31%, and 36% brackets.  Above
	    # that is 39.6%.
	    #
	    #	status	C1	C2	C3	C4

	    cat <<-'!'
		s	24000	58150	121300	263750
		mj	40100	96900	147700	263750
		ms	20050	48450	 73850	131875
		hh	32150	83050	134500	263750
		!
	    ;;

# CONSTANTS FOR 1997 (based on 1997 1040ES) (each exemption = $2650):

	97 )
	    # Constants are tops of 15%, 28%, 31%, and 36% brackets.  Above
	    # that is 39.6%.
	    #
	    #	status	C1	C2	C3	C4

	    cat <<-'!'
		s	24650	59750	124650	271050
		mj	41200	99600	151750	271050
		ms	20600	49800	 75875	135525
		hh	33050	85350	138200	271050
		!
	    ;;

# CONSTANTS FOR 1998 (based on 1998 1040ES) (each exemption = $2700):

	98 )
	    # Constants are tops of 15%, 28%, 31%, and 36% brackets.  Above
	    # that is 39.6%.
	    #
	    #	status	C1	C2	C3	C4

	    cat <<-'!'
		s	25350	61400	128100	278450
		mj	42350  102350	155950	278450
		ms	21175	51150	 77975	139225
		hh	33950	87700	142000	278450
		!
	    ;;

# CONSTANTS FOR 1999 (based on 1999 1040ES) (each exemption = $2750):

	99 )
	    # Constants are tops of 15%, 28%, 31%, and 36% brackets.  Above
	    # that is 39.6%.
	    #
	    #	status	C1	C2	C3	C4

	    cat <<-'!'
		s	25750	62450	130250	283150
		mj	43050  104050	158550	283150
		ms	21525	52025	 79275	141575
		hh	34550	89150	144400	283150
		!
	    ;;

# CONSTANTS FOR 2000 (based on 2000 1040ES) (each exemption = $2800):

	00 )
	    # Constants are tops of 15%, 28%, 31%, and 36% brackets.  Above
	    # that is 39.6%.
	    #
	    #	status	C1	C2	C3	C4

	    cat <<-'!'
		s	26250	63550	132600	288350
		ms	21925	52975	 80725	144175
		mj	43850  105950	161450	288350
		hh	35150	90800	147050	288350
		!
	    ;;

# CONSTANTS FOR 2001 (based on 2001 1040ES) (each exemption = $2900):

	01 )
	    # Constants are tops of 15%, 27.5%, 30.5%, and 35.5% brackets.
	    # Above that is 39.1%.
	    #
	    #	status	C1	C2	C3	C4

	    cat <<-'!'
		s	27050	65550	136750	297350
		mj	45200  109250	166500	297350
		ms	22600	54625	 83250	148675
		hh	36250	93650	151650	297350
		!
	    ;;

# CONSTANTS FOR 2002 (based on 2002 1040ES) (each exemption = $3000):

	02 )
	    # Constants are tops of 10%, 15%, 27%, 30%, and 35% brackets.
	    # Above that is 38.6%.
	    #
	    #	status	C1	C2	C3	C4	C5

	    cat <<-'!'
		s	 6000	27950	67700	141250	307050
		mj	12000	46700  112850	171950	307050
		ms	 6000	23350	56425	 85975	153625
		hh	10000	37450	96700	156600	307050
		!
	    ;;

# CONSTANTS FOR 2003 (based on 2003 1040ES) (each exemption = $3050):
#
# "Long-term capital gains rates.  Effective for sales of assets on or after
# May 6, 2003, the new law reduced the maximum rate on long-term capital gains
# (those on assets owned for more than a year).  Through 2009, taxpayers in the
# higher income-tax brackets will pay a capital gains rate of 15% (down from
# 20% previously), while those in the 10% and 15% brackets will pay a rate of
# 5% through 2007 and 0% in 2008...  Qualified dividend income.  As of January
# 1, 2003, tax rates on "qualified dividend income" (QDI).generally dividends
# generated from stock or stock mutual funds.have been reduced to the same
# rates as those for long-term capital gains..."
#
# Also note marriage penalty abatement, now C2 for MJ is 2x for S.

	03 )
	    # Constants are tops of 10%, 15%, 25%, 28%, and 33% brackets.
	    # Above that is 35%.
	    #
	    #	status	C1	C2	C3	C4	C5

	    cat <<-'!'
		s	 7000	28400	68800	143500	311950
		mj	14000	56800  114650	174700	311950
		ms	 7000	28400	57325	 87350	155975
		hh	10000	38050	98250	159100	311950
		!
	    ;;

# CONSTANTS FOR 2004 (based on 2004 1040ES) (each exemption = $3100):

	04 )
	    # Constants are tops of 10%, 15%, 25%, 28%, and 33% brackets.
	    # Above that is 35% (same as revised in TY 2003).
	    #
	    #	status	C1	C2	C3	C4	C5

	    cat <<-'!'
		s	 7150	29050	70350	146750	319100
		mj	14300	58100  117250	178650	319100
		ms	 7150	29050	58625	 89325	159550
		hh	10200	38900  100500	162700	319100
		!
	    ;;

# CONSTANTS FOR 2005 (based on 2005 1040ES) (each exemption = $3200):

	05 )
	    # Constants are tops of 10%, 15%, 25%, 28%, and 33% brackets.
	    # Above that is 35% (same as revised in TY 2003).
	    #
	    #	status	C1	C2	C3	C4	C5

	    cat <<-'!'
		s	 7300	29700	71950	150150	326450
		mj	14600	59400  119950	182800	326450
		ms	 7300	29700	59975	 91400	163225
		hh	10450	39800  102800	166450	326450
		!
	    ;;

# CONSTANTS FOR 2006 (based on 2006 1040ES) (each exemption = $3300):

	06 )
	    # Constants are tops of 10%, 15%, 25%, 28%, and 33% brackets.
	    # Above that is 35% (same as revised in TY 2003).
	    #
	    #	status	C1	C2	C3	C4	C5

	    cat <<-'!'
		s	 7550	30650	74200	154800	336550
		mj	15100	61300  123700	188450	336550
		ms	 7550	30650	61850	 94225	168275
		hh	10750	41050  106000	171650	336550
		!
	    ;;

# CONSTANTS FOR 2007 (based on 2007 1040ES) (each exemption = $3400):

	07 )
	    # Constants are tops of 10%, 15%, 25%, 28%, and 33% brackets.
	    # Above that is 35% (same as revised in TY 2003).
	    #
	    #	status	C1	C2	C3	C4	C5

	    cat <<-'!'
		s	 7825	31850	77100	160850	349700
		mj	15650	63700  128500	195850	349700
		ms	 7825	31850	64250	 97925	174850
		hh	11200	42650  110100	178350	349700
		!
	    ;;

# CONSTANTS FOR 2008 (based on 2008 1040ES) (each exemption = $3500):

	08 )
	    # Constants are tops of 10%, 15%, 25%, 28%, and 33% brackets.
	    # Above that is 35% (same as revised in TY 2003).
	    #
	    #	status	C1	C2	C3	C4	C5

	    cat <<-'!'
		s	 8025	32550	78850	164550	357700
		mj	16050	65100  131450	200300	357700
		ms	 8025	32550	65725	100150	178850
		hh	11450	43650  112650	182400	357700
		!
	    ;;

# CONSTANTS FOR 2009 (based on 2009 1040ES) (each exemption = $3650):

	09 )
	    # Constants are tops of 10%, 15%, 25%, 28%, and 33% brackets.
	    # Above that is 35% (same as revised in TY 2003).
	    #
	    #	status	C1	C2	C3	C4	C5

	    cat <<-'!'
		s	 8350	33950	82250	171550	372950
		mj	16700	67900  137050	208950	372950
		ms	 8350	33950	68525	104425	196475
		hh	11950	45500  117450	190200	372950
		!
	    ;;

# CONSTANTS FOR 2010 (based on 2010 1040ES) (each exemption = $3650, unchanged):

	10 )
	    # Constants are tops of 10%, 15%, 25%, 28%, and 33% brackets.
	    # Above that is 35% (same as revised in TY 2003).
	    #
	    #	status	C1	C2	C3	C4	C5

	    cat <<-'!'
		s	 8375	34000	82400	171850	373650
		mj	16750	68000  137300	209250	373650
		ms	 8375	34000	68650	104625	186825
		hh	11950	45550  117650	190550	373650
		!
	    ;;

# CONSTANTS FOR 2011 (based on 2011 1040ES) (each exemption = $3700):

	11 )
	    # Constants are tops of 10%, 15%, 25%, 28%, and 33% brackets.
	    # Above that is 35% (same as revised in TY 2003).
	    #
	    #	status	C1	C2	C3	C4	C5

	    cat <<-'!'
                s        8500   34500   83600   174400  379150
                mj      17000   69000  139350   212300  379150
                ms       8500   34500   69675   106150  189575
                hh      12150   46250  119400   193350  379150
		!
            ;;

# CONSTANTS FOR 2012 (based on 2012 1040ES) (each exemption = $3800):

	12 )
	    # Constants are tops of 10%, 15%, 25%, 28%, and 33% brackets.
	    # Above that is 35% (same as revised in TY 2003).
	    #
	    #	status	C1	C2	C3	C4	C5

	    cat <<-'!'
                s        8700   35350   85650   178650  388350
                mj      17400   70700  142700   217450  388350
                ms       8700   35350   71350   108725  194175
                hh      12400   47350  122300   198050  388350
		!
            ;;

	esac |				# note piping of output.


# FIGURE TAX:
#
# Uses constants piped to standard input, and script arguments, with taxable
# income already adjusted to center of bracket.
#
# Note:  I know, this could be a lot shorter (although more complex) if it was
# parameterized better...

	if [[ $# -ge 3 ]]
	then

# 1987:

	    if [[ $1 = 87 ]]
	    then
		awk '

		# Save appropriate constants for given status:

		($1 == "'$2'") { C1 = $2; C2 = $3; C3 = $4; C4 = $5 }

		END {
		    ti = '"$3"';

		    tax = 0.11 * ti;

		    if (ti > C1)	tax += 0.04  * (ti - C1);
		    if (ti > C2)	tax += 0.13  * (ti - C2);
		    if (ti > C3)	tax += 0.07  * (ti - C3);
		    if (ti > C4)	tax += 0.035 * (ti - C4);

		    # round to whole dollar; exact half dollar rounds up:

		    if (ti <= 100000) printf ("%.0f\n", tax + 0.0001);
		    else	      printf ("%.2f\n", tax);
		}'

# 1988 - 1990:

	    elif [[ ($1 = 88) || ($1 = 89) || ($1 = 90) ]]
	    then
		awk '

		# Save appropriate constants for given status:

		($1 == "'$2'") { C1 = $2; C2 = $3; C3 = $4; K = $5 }

		END {
		    ti = '"$3"';

		    if (ti <= C3)	# due to non-linearity.
		    {
			tax = 0.15 * ti;

			if (ti > C1)	tax += 0.13 * (ti - C1);
			if (ti > C2)	tax += 0.05 * (ti - C2);
		    }
		    else		# handle high-income case.
		    {
			tax = 0.28 * ti;

			if ((excess = ('"$4"' * K)) > (ti - C3))
			    excess = ti - C3;

			tax += 0.05 * excess;
		    }

		    # round to whole dollar; exact half dollar rounds up:

		    if (ti <= 100000) printf ("%.0f\n", tax + 0.0001);
		    else	      printf ("%.2f\n", tax);
		}'

# 1991 - 1992:

	    elif [[ ($1 = 91) || ($1 = 92) ]]
	    then
		awk '

		# Save appropriate constants for given status:

		($1 == "'$2'") { C1 = $2; C2 = $3 }

		END {
		    ti = '"$3"';

		    tax = 0.15 * ti;

		    if (ti > C1)	tax += 0.13 * (ti - C1);
		    if (ti > C2)	tax += 0.03 * (ti - C2);

		    # round to whole dollar; exact half dollar rounds up:

		    if (ti <= 100000) printf ("%.0f\n", tax + 0.0001);
		    else	      printf ("%.2f\n", tax);
		}'

# 1993 - 2000:

	    elif [[ (${1#0} -ge 93) || (${1#0} = 00) ]]
	    then
		awk '

		# Save appropriate constants for given status:

		($1 == "'$2'") { C1 = $2; C2 = $3; C3 = $4; C4 = $5 }

		END {
		    ti = '"$3"';

		    tax = 0.15 * ti;

		    if (ti > C1)	tax += 0.13  * (ti - C1);
		    if (ti > C2)	tax += 0.03  * (ti - C2);
		    if (ti > C3)	tax += 0.05  * (ti - C3);
		    if (ti > C4)	tax += 0.036 * (ti - C4);

		    # round to whole dollar; exact half dollar rounds up:

		    if (ti <= 100000) printf ("%.0f\n", tax + 0.0001);
		    else	      printf ("%.2f\n", tax);
		}'

# 2001:

	    elif [[ $1 = 01 ]]
	    then
		awk '

		# Save appropriate constants for given status:

		($1 == "'$2'") { C1 = $2; C2 = $3; C3 = $4; C4 = $5 }

		END {
		    ti = '"$3"';

		    tax = 0.15 * ti;

		    if (ti > C1)	tax += 0.125 * (ti - C1);
		    if (ti > C2)	tax += 0.03  * (ti - C2);
		    if (ti > C3)	tax += 0.05  * (ti - C3);
		    if (ti > C4)	tax += 0.036 * (ti - C4);

		    # round to whole dollar; exact half dollar rounds up:

		    if (ti <= 100000) printf ("%.0f\n", tax + 0.0001);
		    else	      printf ("%.2f\n", tax);
		}'

# 2002:

	    elif [[ $1 = 02 ]]
	    then
		awk '

		# Save appropriate constants for given status:

		($1 == "'$2'") { C1 = $2; C2 = $3; C3 = $4; C4 = $5; C5 = $6 }

		END {
		    ti = '"$3"';

		    tax = 0.10 * ti;

		    if (ti > C1)	tax += 0.05  * (ti - C1);
		    if (ti > C2)	tax += 0.12  * (ti - C2);
		    if (ti > C3)	tax += 0.03  * (ti - C3);
		    if (ti > C4)	tax += 0.05  * (ti - C4);
		    if (ti > C5)	tax += 0.036 * (ti - C5);

		    # round to whole dollar; exact half dollar rounds up:

		    if (ti <= 100000) printf ("%.0f\n", tax + 0.0001);
		    else	      printf ("%.2f\n", tax);
		}'

# 2003 - 2011:

	    elif [[ ($1 = 03) \
		 || ($1 = 04) \
		 || ($1 = 05) \
		 || ($1 = 06) \
		 || ($1 = 07) \
		 || ($1 = 08) \
		 || ($1 = 09) \
		 || ($1 = 10) \
		 || ($1 = 11) \
		 || ($1 = 12) \
	    ]]
	    then
		awk '

		# Save appropriate constants for given status:

		($1 == "'$2'") { C1 = $2; C2 = $3; C3 = $4; C4 = $5; C5 = $6 }

		END {
		    ti = '"$3"';

		    tax = 0.10 * ti;

		    if (ti > C1)	tax += 0.05 * (ti - C1);
		    if (ti > C2)	tax += 0.10 * (ti - C2);
		    if (ti > C3)	tax += 0.03 * (ti - C3);
		    if (ti > C4)	tax += 0.05 * (ti - C4);
		    if (ti > C5)	tax += 0.02 * (ti - C5);

		    # round to whole dollar; exact half dollar rounds up:

		    if (ti <= 100000) printf ("%.0f\n", tax + 0.0001);
		    else	      printf ("%.2f\n", tax);
		}'


# TAIL END:
#
# This also makes it easier to add new sections above.

	    else
		echo >&1 "$0: Internal error, \$1 = \"$1\" unexpected."
		exit 1
	    fi


# PREPARE TO PLOT RATE CHART:
#
# Note that stdin is piped from cat's above.
#
# If two args, call the script recursively (before cd'ing) to get the data for
# the second year; then do the first year.

	else
	    [[ $# = 1 ]] || TAXRECURSE=1 $0 $2	# recurse for second year.

	    mkdir -p $plotdir			# ensure already made.
	    cd $plotdir

	    [[ ($1 -ge 91) || ($1 -lt 50) ]] && maxti='100000'	# wider plot.

# 1987:

	    if [[ $1 = 87 ]]
	    then
		awk '{
		    stat = $1 "'"$1"'";		# name of status.
		    $1   = 0;			# reuse $1 as base number.
		    tax  = 0;
		    split ("0 0.11 0.15 0.28 0.35 0.385", rate);

		    # Set upper bound in constants array:

		    for (step = 2; step <= 5; ++step)
			if ($step >= '$maxti')
			    break;

		    $step	= '$maxti';		# replace or append.
		    $(step + 1)	= '$maxti' + 1;

		    print ".", 0, 0  > stat;

		    for (step = 2; $step <= '$maxti'; ++step)
		    {
			tax += (rate [step]) * ($step - $(step - 1));
			print ".", $step, tax > stat;
		    }
		}'

# 1988 - 1990:

	    elif [[ ($1 = 88) || ($1 = 89) || ($1 = 90) ]]
	    then
		awk '{
		    stat = $1 "'"$1"'";		# name of status.
		    $1   = 0;			# reuse $1 as base number.
		    tax  = 0;
		    split ("0 0.15 0.28 0.33 0", rate);

		    # Set upper bound in constants array:

		    for (step = 2; step <= 4; ++step)
			if ($step >= '$maxti')
			    break;

		    if (step == 5)	# top constant is less than $maxti.
		    {
			print "'"$0"':  warning:  inaccurate plot for status", \
			    stat, "above $" $4;
		    }

		    $step	= '$maxti';		# replace or append.
		    $(step + 1)	= '$maxti' + 1;

		    print ".", 0, 0  > stat;

		    for (step = 2; $step <= '$maxti'; ++step)
		    {
			tax += (rate [step]) * ($step - $(step - 1));
			print ".", $step, tax > stat;
		    }
		}'

# 1991 - 1992:

	    elif [[ ($1 = 91) || ($1 = 92) ]]
	    then
		awk '{
		    stat = $1 "'"$1"'";		# name of status.
		    $1   = 0;			# reuse $1 as base number.
		    tax  = 0;
		    split ("0 0.15 0.28 0.31", rate);

		    # Set upper bound in constants array:

		    for (step = 2; step <= 3; ++step)
			if ($step >= '$maxti')
			    break;

		    $step	= '$maxti';		# replace or append.
		    $(step + 1)	= '$maxti' + 1;

		    print ".", 0, 0  > stat;

		    for (step = 2; $step <= '$maxti'; ++step)
		    {
			tax += (rate [step]) * ($step - $(step - 1));
			print ".", $step, tax > stat;
		    }
		}'

# 1993 - 2000:

	    elif [[ ($1 -ge 93) || ($1 = 00) ]]
	    then
		awk '{
		    stat = $1 "'"$1"'";		# name of status.
		    $1   = 0;			# reuse $1 as base number.
		    tax  = 0;
		    split ("0 0.15 0.28 0.31 0.36 0.396", rate);

		    # Set upper bound in constants array:

		    for (step = 2; step <= 5; ++step)
			if ($step >= '$maxti')
			    break;

		    $step	= '$maxti';		# replace or append.
		    $(step + 1)	= '$maxti' + 1;

		    print ".", 0, 0  > stat;

		    for (step = 2; $step <= '$maxti'; ++step)
		    {
			tax += (rate [step]) * ($step - $(step - 1));
			print ".", $step, tax > stat;
		    }
		}'

# 2001:

	    elif [[ $1 = 01 ]]
	    then
		awk '{
		    stat = $1 "'"$1"'";		# name of status.
		    $1   = 0;			# reuse $1 as base number.
		    tax  = 0;
		    # See file header comments:
		    split ("0 0.15 0.275 0.305 0.355 0.391", rate);

		    # Set upper bound in constants array:

		    for (step = 2; step <= 5; ++step)
			if ($step >= '$maxti')
			    break;

		    $step	= '$maxti';		# replace or append.
		    $(step + 1)	= '$maxti' + 1;

		    print ".", 0, 0  > stat;

		    for (step = 2; $step <= '$maxti'; ++step)
		    {
			tax += (rate [step]) * ($step - $(step - 1));
			print ".", $step, tax > stat;
		    }
		}'

# 2002:

	    else
		awk '{
		    stat = $1 "'"$1"'";		# name of status.
		    $1   = 0;			# reuse $1 as base number.
		    tax  = 0;
		    # See file header comments:
		    split ("0 0.10 0.15 0.27 0.30 0.35 0.386", rate);

		    # Set upper bound in constants array:

		    for (step = 2; step <= 6; ++step)
			if ($step >= '$maxti')
			    break;

		    $step	= '$maxti';		# replace or append.
		    $(step + 1)	= '$maxti' + 1;

		    print ".", 0, 0  > stat;

		    for (step = 2; $step <= '$maxti'; ++step)
		    {
			tax += (rate [step]) * ($step - $(step - 1));
			print ".", $step, tax > stat;
		    }
		}'
	    fi


# PLOT RATE CHART:
#
# Filenames, hence curves, are ordered highest to lowest so they
# look rational on a monochrome display:

	    if [[ -z "$TAXRECURSE" ]]		# else don't plot now.
	    then
		if [[ $# = 1 ]]			# single year only:
		    then
		    [[ $1 -lt 50 ]] && century='20' || century='19'

		    dataplot -Gx -t0 $spool $device $driver		\
			"US Federal Tax Rates, $century$1"		\
			'Based on filing status' 'Taxable Income' 'Tax'	\
			ms* s* hh* mj*

		else				# multiple years:
		    [[ $1 -lt 50 ]] && century1='20' || century1='19'
		    [[ $2 -lt 50 ]] && century2='20' || century2='19'

		    dataplot -Gx -t0,1,0,1,0,1,0,1 -c1,1,2,2,3,3,4,4	 \
			$spool $device $driver				 \
			"US Federal Tax Rates, $century1$1 + $century2$2"\
			'Based on filing status' 'Taxable Income' 'Tax'	 \
			ms* s* hh* mj*
		fi
	    fi

	    cd ..			# so $plotdir is removable.

	    # Unfortunately "trap" doesn't work:

	    [[ -n "$TAXRECURSE" ]] || rm -r $plotdir
	fi