@x
@!interrupt:integer; {should \TeX\ pause for instructions?}
@!OK_to_interrupt:boolean; {should interrupts be observed?}

@ @<Set init...@>=
interrupt:=0; OK_to_interrupt:=true;
@y
@!interrupt:integer; {should \TeX\ pause for instructions?}
@!OK_to_interrupt:boolean; {should interrupts be observed?}
@!two_to_the: array[0..30] of integer; {$|two_to_the|[k]=2^k$}

@ @<Set init...@>=
interrupt:=0; OK_to_interrupt:=true;
two_to_the[0]:=1;
for i:=1 to 30 do two_to_the[i]:=two_to_the[i-1]+two_to_the[i-1];
@z

@x
@ When \TeX\ ``packages'' a list into a box, it needs to calculate the
proportionality ratio by which the glue inside the box should stretch
or shrink. This calculation does not affect \TeX's decision making,
so the precise details of rounding, etc., in the glue calculation are not
of critical importance for the consistency of results on different computers.

We shall use the type |glue_ratio| for such proportionality ratios.
A glue ratio should take the same amount of memory as an
|integer| (usually 32 bits) if it is to blend smoothly with \TeX's
other data structures. Thus |glue_ratio| should be equivalent to
|short_real| in some implementations of \PASCAL. Alternatively,
it is possible to deal with glue ratios using nothing but fixed-point
arithmetic; see {\sl TUGboat \bf3},1 (March 1982), 10--27. (But the
routines cited there must be modified to allow negative glue ratios.)
@^system dependencies@>

@d set_glue_ratio_zero(#) == #:=0.0 {store the representation of zero ratio}
@d set_glue_ratio_one(#) == #:=1.0 {store the representation of unit ratio}
@d float(#) == # {convert from |glue_ratio| to type |real|}
@d unfloat(#) == # {convert from |real| to type |glue_ratio|}
@d float_constant(#) == #.0 {convert |integer| constant to |real|}
@y
@ When \TeX\ ``packages'' a list into a box, it needs to calculate the
proportionality ratio by which the glue inside the box should stretch
or shrink. This calculation does not affect \TeX's decision making,
so the precise details of rounding, etc., in the glue calculation are not
of critical importance for the consistency of results on different computers.

We shall use the type |glue_ratio| for such proportionality ratios.
A glue ratio should take the same amount of memory as an
|integer| (usually 32 bits) if it is to blend smoothly with \TeX's
other data structures. Thus |glue_ratio| should be equivalent to
|short_real| in some implementations of \PASCAL. Alternatively,
it is possible to deal with glue ratios using nothing but fixed-point
arithmetic; see {\sl TUGboat \bf3},1 (March 1982), 10--27. (But the
routines cited there must be modified to allow negative glue ratios.)

This is what we do here. Our implementation stores |a+16| in the
low five bits, |b| in the next five bits and |c+@'100000| in the
next 17 bits of the integer |glue_ratio|. The procedures
|pack_glue_ratio| and |unpack_glue_ratio| are used to convert
to and from this format. A more efficient implementation would
inline these prodedures and use shifting.

@d glue_ratio_zero == 33554480 {|pack_glue_ratio(16,1,0)=33554480|}
@d glue_ratio_one == 33556528 {|pack_glue_ratio(16,1,2)=33556528|}
@d set_glue_ratio_zero(#) == #:=glue_ratio_zero
@d set_glue_ratio_one(#) == #:=glue_ratio_one
@z

@x
@!glue_ratio=real; {one-word representation of a glue expansion factor}
@y
@!glue_ratio=real; {one-word representation of a glue expansion factor}
@!glue_ratio=integer; {one-word representation of a glue expansion factor}

@ Before we can state the glue-multiplication function |glue_mult|, we need
routines for packing and unpacking |glue_ratio|s.

@p @!debug procedure check_range(l,h:integer; s:str_number; var v:integer);
begin
 if v<l then begin
   v:=l;
   print_err(s); print(" too small");
 end else if v>h then begin
   v:=h;
   print_err(s); print(" too large");
 end;
end;
gubed

function pack_glue_ratio(a,b,c:integer):glue_ratio;
begin
 c:=c+@'100000;
 @!debug
 check_range(1,31,"pack_glue_ratio: a",a);
 check_range(0,30,"pack_glue_ratio: b",b);
 check_range(0,@'200000,"pack_glue_ratio: c",c);
 gubed
 pack_glue_ratio:=a+@'40*b+@'2000*c;
end;

procedure unpack_glue_ratio(g:glue_ratio; var a,b,c:integer);
begin
 c:=(g mod @'1000000000) div @'2000;
 b:=(g mod @'2000) div @'40;
 a:=g mod @'40;
 @!debug
 check_range(1,31,"unpack_glue_ratio: a",a);
 check_range(0,30,"unpack_glue_ratio: b",b);
 check_range(0,@'200000,"unpack_glue_ratio: c",c);
 gubed
 c:=c-@'100000;
end;

function glue_mult(@!x:scaled;@!g:glue_ratio):integer;
var a,b,c:integer;
begin
unpack_glue_ratio(g,a,b,c);
if a>16 then x:=x div two_to_the[a-16] {right shift by |a| places}
else x:=x*two_to_the[16-a]; {left shift by |-a| places}
glue_mult:=(x*c) div two_to_the[b]; {right shift by |b| places}
 end; {note that |b| may be as large as 30}

@*Glue setting.
The |glue_fix| function computes |a|, |b|, and |c| by the method
explained in {\sl TUGboat \bf3},1 (March 1982), 10--27. This
implementation differs from the one given there in that it treats negative
values of |s| properly. To do so, we allow |c| to range from -@'100000 to
@'100000 and store it shifted by @'100000.

|glue_fix| returns a |glue_ratio| approximation of |t/s|.

@p function glue_fix(@!s,@!t,@!y:scaled):glue_ratio;
var @!a,@!b,@!c:integer; {components of the desired ratio}
@!k,@!h:integer; {$30-\lfloor\lg s\rfloor$, $30-\lfloor\lg t\rfloor$}
@!s0:integer; {original (unnormalized) value of |s|}
@!q,@!r,@!s1:integer; {quotient, remainder, divisor}
@!w:integer; {$2^l$, where $l=16-k$}
@!negative:boolean;
begin
negative:=false;
if s<0 then begin
  negative:=true;
  s:=-s;
end;
if y=0 then begin
  print("glue_fix: y=0. Why?"); 
  glue_fix:=pack_glue_ratio(a+16,b,c);
end else begin
@<Normalize |s|, |t|, and |y|, computing |a|, |k|, and |h|@>;
if t<s then b:=15-a-k+h@+else b:=14-a-k+h;
if (b<0) or (b>30) then
  begin if b<0 then
    begin
      print_err("Excessive glue");
@.Excessive glue@>
      help2("I can't work with sizes bigger than about 19 feet.")@/
           ("Proceed, with fingers crossed.");@/
      error;
  end;
  b:=0; c:=0; {make |f(x)| identically zero}
  end
else begin if k>=16 then {easy case, $s_0<2^{15}$}
    c:=(t div two_to_the[h-a-b]+s0-1) div s0 {here |1<=h-a-b<=k-14<=16|}
  else @<Compute |c| by long division@>;
  end;
if negative then c:=-c;
glue_fix:=pack_glue_ratio(a+16,b,c);
end;
end;

@ @<Normalize |s|, |t|, and |y|, computing |a|, |k|, and |h|@>=
begin a:=15; k:=0; h:=0; s0:=s;
while y<@'10000000000 do {|y| is known to be positive}
  begin decr(a); y:=y+y;
  end;
while s<@'10000000000 do {|s| is known to be positive}
  begin incr(k); s:=s+s;
  end;
while t<@'10000000000 do {|t| is known to be positive}
  begin incr(h); t:=t+t;
  end;
end {now $2^{30}\le t=2^ht_0<2^{31}$ and $2^{30}\le s=2^ks_0<2^{31}$,
  hence $d=k-h$ if $t/s<1$}

@ @<Compute |c| by long division@>=
begin w:=two_to_the[16-k];
s1:=s0 div w;
q:=t div s1;
r:=((t mod s1)*w)-((s0 mod w)*q);
if r>0 then
  begin incr(q); r:=r-s0;
  end
else while r<=-s0 do
  begin decr(q); r:=r+s0;
  end;
if a+b+k-h=15 then c:=(q+1) div 2 @+else c:=(q+3) div 4;
end
@z

@x
@p @!debug procedure print_word(@!w:memory_word);
  {prints |w| in all ways}
begin print_int(w.int); print_char(" ");@/
print_scaled(w.sc); print_char(" ");@/
print_scaled(round(unity*float(w.gr))); print_ln;@/
@^real multiplication@>
print_int(w.hh.lh); print_char("="); print_int(w.hh.b0); print_char(":");
print_int(w.hh.b1); print_char(";"); print_int(w.hh.rh); print_char(" ");@/
print_int(w.qqqq.b0); print_char(":"); print_int(w.qqqq.b1); print_char(":");
print_int(w.qqqq.b2); print_char(":"); print_int(w.qqqq.b3);
end;
gubed
@y
@p procedure print_gr(@!g:glue_ratio); {prints a glue multiplier}
var @!j:-29..31; {the amount to shift |c|}
 a,b,c:integer;
begin
unpack_glue_ratio(g,a,b,c);
j:=32-a-b;
while j>15 do
  begin print("2x"); decr(j); {indicate multiples of 2 for BIG cases}
  end;
if j<0 then print_scaled(c div two_to_the[-j]) {shift right}
else print_scaled(c*two_to_the[j]); {shift left}
end;

@!debug procedure print_word(@!w:memory_word);
  {prints |w| in all ways}
begin print_int(w.int); print_char(" ");@/
print_scaled(w.sc); print_char(" ");@/
print_gr(w.gr); print_ln;@/
print_int(w.hh.lh); print_char("="); print_int(w.hh.b0); print_char(":");
print_int(w.hh.b1); print_char(";"); print_int(w.hh.rh); print_char(" ");@/
print_int(w.qqqq.b0); print_char(":"); print_int(w.qqqq.b1); print_char(":");
print_int(w.qqqq.b2); print_char(":"); print_int(w.qqqq.b3);
end;
gubed
@z

@x
@p procedure show_node_list(@!p:integer); {prints a node list symbolically}
label exit;
var n:integer; {the number of items already printed at this level}
@!g:real; {a glue ratio, as a floating point number}
@y
@p procedure show_node_list(@!p:integer); {prints a node list symbolically}
label exit;
var n:integer; {the number of items already printed at this level}
@!g:glue_ratio; {a glue ratio, as a floating point number}
a,b,c,j:integer;
@z

@x
@ The code will have to change in this place if |glue_ratio| is
a structured type instead of an ordinary |real|. Note that this routine
should avoid arithmetic errors even if the |glue_set| field holds an
arbitrary random value. The following code assumes that a properly
formed nonzero |real| number has absolute value $2^{20}$ or more when
it is regarded as an integer; this precaution was adequate to prevent
floating point underflow on the author's computer.
@^system dependencies@>
@^dirty \PASCAL@>

@<Display the value of |glue_set(p)|@>=
g:=float(glue_set(p));
if (g<>float_constant(0))and(glue_sign(p)<>normal) then
  begin print(", glue set ");
  if glue_sign(p)=shrinking then print("- ");
  if abs(mem[p+glue_offset].int)<@'4000000 then print("?.?")
  else if abs(g)>float_constant(20000) then
    begin if g>float_constant(0) then print_char(">")
    else print("< -");
    print_glue(20000*unity,glue_order(p),0);
    end
  else print_glue(round(unity*g),glue_order(p),0);
@^real multiplication@>
  end
@y
@ The code has been changed here, since |glue_ratio| is no longer |real|.
Note that this routine should avoid arithmetic errors even if the |glue_set|
field holds an arbitrary random value.

@<Display the value of |glue_set(p)|@>=
if (glue_ratio_zero<>glue_set(p))and(glue_sign(p)<>normal) then begin
  print(", glue set ");
  if glue_sign(p)=shrinking then print("- ");
  if abs(mem[p+glue_offset].int)<@'4000000 then print("?.?")
  else if abs(g)>float_constant(20000) then
  begin end;
  print_gr(glue_set(p));
  case glue_order(p) of
  normal: do_nothing;
  fil: print("fil");
  fill: print("fill");
  filll: print("filll");
  othercases print("foul")
  endcases
end;
@z

@x
@!glue_temp:real; {glue value before rounding}
@y
@!glue_temp:scaled; {glue value before rounding}
@z

@x
@ @d vet_glue(#)== glue_temp:=#;
  if glue_temp>float_constant(1000000000) then
           glue_temp:=float_constant(1000000000)
  else if glue_temp<-float_constant(1000000000) then
           glue_temp:=-float_constant(1000000000)
@y
@ @d vet_glue(#)== glue_temp:=#;
  if glue_temp>1000000000 then glue_temp:=1000000000
  else if glue_temp<-1000000000 then glue_temp:=-1000000000
@z

@x
@<Move right or output leaders@>=
begin g:=glue_ptr(p); rule_wd:=width(g);
if g_sign<>normal then
  begin if g_sign=stretching then
    begin if stretch_order(g)=g_order then
      begin vet_glue(float(glue_set(this_box))*stretch(g));
@^real multiplication@>
      rule_wd:=rule_wd+round(glue_temp);
      end;
    end
  else if shrink_order(g)=g_order then
    begin vet_glue(float(glue_set(this_box))*shrink(g));
      rule_wd:=rule_wd-round(glue_temp);
    end;
  end;
@y
@<Move right or output leaders@>=
begin g:=glue_ptr(p); rule_wd:=width(g);
if g_sign<>normal then
  begin if g_sign=stretching then
    begin if stretch_order(g)=g_order then
      begin
        vet_glue(glue_mult(stretch(g),glue_set(this_box)));
        rule_wd:=rule_wd+glue_temp;
      end;
    end
  else if shrink_order(g)=g_order then
    begin
      vet_glue(glue_mult(shrink(g),glue_set(this_box)));
      rule_wd:=rule_wd-glue_temp;
    end;
  end;
@z

@x
@!glue_temp:real; {glue value before rounding}
@y
@!glue_temp:scaled; {glue value before rounding}
@z

@x
@ @<Move down or output leaders@>=
begin g:=glue_ptr(p); rule_ht:=width(g);
if g_sign<>normal then
  begin if g_sign=stretching then
    begin if stretch_order(g)=g_order then
      begin vet_glue(float(glue_set(this_box))*stretch(g));
@^real multiplication@>
      rule_ht:=rule_ht+round(glue_temp);
      end;
    end
  else if shrink_order(g)=g_order then
    begin vet_glue(float(glue_set(this_box))*shrink(g));
    rule_ht:=rule_ht-round(glue_temp);
    end;
  end;
@y
@ @<Move down or output leaders@>=
begin g:=glue_ptr(p); rule_ht:=width(g);
if g_sign<>normal then
  begin if g_sign=stretching then
    begin if stretch_order(g)=g_order then
      begin
        vet_glue(glue_mult(stretch(g),glue_set(this_box)));
        rule_ht:=rule_ht+glue_temp;
      end;
    end
  else if shrink_order(g)=g_order then
    begin
      vet_glue(glue_mult(shrink(g),glue_set(this_box)));
      rule_ht:=rule_ht-glue_temp;
    end;
  end;
@z

@x
@!total_stretch, @!total_shrink: array[glue_ord] of scaled;
  {glue found by |hpack| or |vpack|}
@y
@!total_stretch, @!total_shrink, @!max_stretch, @!max_shrink:
  array[glue_ord] of scaled; {glue found by |hpack| or |vpack|}
@z

@x
@ @<Clear dimensions to zero@>=
d:=0; x:=0;
total_stretch[normal]:=0; total_shrink[normal]:=0;
total_stretch[fil]:=0; total_shrink[fil]:=0;
total_stretch[fill]:=0; total_shrink[fill]:=0;
total_stretch[filll]:=0; total_shrink[filll]:=0
@y
@ @<Clear dimensions to zero@>=
d:=0; x:=0;
total_stretch[normal]:=0; total_shrink[normal]:=0;
total_stretch[fil]:=0; total_shrink[fil]:=0;
total_stretch[fill]:=0; total_shrink[fill]:=0;
total_stretch[filll]:=0; total_shrink[filll]:=0;
max_stretch[normal]:=0; max_shrink[normal]:=0;
max_stretch[fil]:=0; max_shrink[fil]:=0;
max_stretch[fill]:=0; max_shrink[fill]:=0;
max_stretch[filll]:=0; max_shrink[filll]:=0
@z

@x
@ @<Incorporate glue into the horizontal totals@>=
begin g:=glue_ptr(p); x:=x+width(g);@/
o:=stretch_order(g); total_stretch[o]:=total_stretch[o]+stretch(g);
o:=shrink_order(g); total_shrink[o]:=total_shrink[o]+shrink(g);
@y
@ @<Incorporate glue into the horizontal totals@>=
begin g:=glue_ptr(p); x:=x+width(g);@/
o:=stretch_order(g); total_stretch[o]:=total_stretch[o]+stretch(g);
if abs(stretch(g))>max_stretch[o] then max_stretch[o]:=abs(stretch(g));
o:=shrink_order(g); total_shrink[o]:=total_shrink[o]+shrink(g);
if abs(shrink(g))>max_shrink[o] then max_shrink[o]:=abs(shrink(g));
@z

@x
@ @<Determine horizontal glue stretch setting...@>=
begin @<Determine the stretch order@>;
glue_order(r):=o; glue_sign(r):=stretching;
if total_stretch[o]<>0 then glue_set(r):=unfloat(x/total_stretch[o])
@^real division@>
else  begin glue_sign(r):=normal;
  set_glue_ratio_zero(glue_set(r)); {there's nothing to stretch}
  end;
@y
@ @<Determine horizontal glue stretch setting...@>=
begin @<Determine the stretch order@>;
glue_order(r):=o; glue_sign(r):=stretching;
if total_stretch[o]<>0 then
  glue_set(r):=glue_fix(total_stretch[o],x,max_stretch[o])
else  begin glue_sign(r):=normal;
  glue_set(r):=glue_ratio_zero; {there's nothing to stretch}
  end;
@z

@x
@ @<Determine horizontal glue shrink setting...@>=
begin @<Determine the shrink order@>;
glue_order(r):=o; glue_sign(r):=shrinking;
if total_shrink[o]<>0 then glue_set(r):=unfloat((-x)/total_shrink[o])
@^real division@>
@y
@ @<Determine horizontal glue shrink setting...@>=
begin @<Determine the shrink order@>;
glue_order(r):=o; glue_sign(r):=shrinking;
if total_shrink[o]<>0 then
  glue_set(r):=glue_fix(total_shrink[o],-x,max_shrink[o])
@z

@x
@ @<Incorporate glue into the vertical totals@>=
begin x:=x+d; d:=0;@/
g:=glue_ptr(p); x:=x+width(g);@/
o:=stretch_order(g); total_stretch[o]:=total_stretch[o]+stretch(g);
o:=shrink_order(g); total_shrink[o]:=total_shrink[o]+shrink(g);
@y
@ @<Incorporate glue into the vertical totals@>=
begin x:=x+d; d:=0;@/
g:=glue_ptr(p); x:=x+width(g);@/
o:=stretch_order(g); total_stretch[o]:=total_stretch[o]+stretch(g);
if abs(stretch(g))>max_stretch[o] then max_stretch[o]:=abs(stretch(g));
o:=shrink_order(g); total_shrink[o]:=total_shrink[o]+shrink(g);
if abs(shrink(g))>max_shrink[o] then max_shrink[o]:=abs(shrink(g));
@z

@x
@ @<Determine vertical glue stretch setting...@>=
begin @<Determine the stretch order@>;
glue_order(r):=o; glue_sign(r):=stretching;
if total_stretch[o]<>0 then glue_set(r):=unfloat(x/total_stretch[o])
@^real division@>
@y
@ @<Determine vertical glue stretch setting...@>=
begin @<Determine the stretch order@>;
glue_order(r):=o; glue_sign(r):=stretching;
if total_stretch[o]<>0 then
  glue_set(r):=glue_fix(total_stretch[o],x,max_stretch[o])
@z

@x
@ @<Determine vertical glue shrink setting...@>=
begin @<Determine the shrink order@>;
glue_order(r):=o; glue_sign(r):=shrinking;
if total_shrink[o]<>0 then glue_set(r):=unfloat((-x)/total_shrink[o])
@^real division@>
@y
@ @<Determine vertical glue shrink setting...@>=
begin @<Determine the shrink order@>;
glue_order(r):=o; glue_sign(r):=shrinking;
if total_shrink[o]<>0 then
  glue_set(r):=glue_fix(total_shrink[o],-x,max_shrink[o])
@z

@x
@ @<Append tabskip glue and an empty box to list |u|...@>=
s:=link(s); v:=glue_ptr(s); link(u):=new_glue(v); u:=link(u);
subtype(u):=tab_skip_code+1; t:=t+width(v);
if glue_sign(p)=stretching then
  begin if stretch_order(v)=glue_order(p) then
    t:=t+round(float(glue_set(p))*stretch(v));
@^real multiplication@>
  end
else if glue_sign(p)=shrinking then
  begin if shrink_order(v)=glue_order(p) then
    t:=t-round(float(glue_set(p))*shrink(v));
  end;
@y
@ @<Append tabskip glue and an empty box to list |u|...@>=
s:=link(s); v:=glue_ptr(s); link(u):=new_glue(v); u:=link(u);
subtype(u):=tab_skip_code+1; t:=t+width(v);
if glue_sign(p)=stretching then
  begin if stretch_order(v)=glue_order(p) then
    t:=t+glue_mult(stretch(v),glue_set(p));
  end
else if glue_sign(p)=shrinking then
  begin if shrink_order(v)=glue_order(p) then
    t:=t-glue_mult(shrink(v),glue_set(p));
  end;
@z

@x
@ @<Make the unset node |r| into an |hlist_node| of width |w|...@>=
begin height(r):=height(q); depth(r):=depth(q);
if t=width(r) then
  begin glue_sign(r):=normal; glue_order(r):=normal;
  set_glue_ratio_zero(glue_set(r));
  end
else if t>width(r) then
  begin glue_sign(r):=stretching;
  if glue_stretch(r)=0 then set_glue_ratio_zero(glue_set(r))
  else glue_set(r):=unfloat((t-width(r))/glue_stretch(r));
@^real division@>
  end
else  begin glue_order(r):=glue_sign(r); glue_sign(r):=shrinking;
  if glue_shrink(r)=0 then set_glue_ratio_zero(glue_set(r))
  else if (glue_order(r)=normal)and(width(r)-t>glue_shrink(r)) then
    set_glue_ratio_one(glue_set(r))
  else glue_set(r):=unfloat((width(r)-t)/glue_shrink(r));
  end;
width(r):=w; type(r):=hlist_node;
end
@y
@ @<Make the unset node |r| into an |hlist_node| of width |w|...@>=
begin height(r):=height(q); depth(r):=depth(q);
if t=width(r) then
  begin glue_sign(r):=normal; glue_order(r):=normal;
  glue_set(r):=glue_ratio_zero;
  end
else if t>width(r) then
  begin glue_sign(r):=stretching;
  if glue_stretch(r)=0 then glue_set(r):=glue_ratio_zero
  else
   glue_set(r):=glue_fix(glue_stretch(r),t-width(r),abs(glue_stretch(r)/2));
  end
else  begin glue_order(r):=glue_sign(r); glue_sign(r):=shrinking;
  if glue_shrink(r)=0 then glue_set(r):=glue_ratio_zero
  else if (glue_order(r)=normal)and(width(r)-t>glue_shrink(r)) then
    glue_set(r):=glue_ratio_one
  else
   glue_set(r):=glue_fix(glue_shrink(r),width(r)-t,abs(glue_shrink(r)/2));
  end;
width(r):=w; type(r):=hlist_node;
end
@z

@x
@ @<Make the unset node |r| into a |vlist_node| of height |w|...@>=
begin width(r):=width(q);
if t=height(r) then
  begin glue_sign(r):=normal; glue_order(r):=normal;
  set_glue_ratio_zero(glue_set(r));
  end
else if t>height(r) then
  begin glue_sign(r):=stretching;
  if glue_stretch(r)=0 then set_glue_ratio_zero(glue_set(r))
  else glue_set(r):=unfloat((t-height(r))/glue_stretch(r));
@^real division@>
  end
else  begin glue_order(r):=glue_sign(r); glue_sign(r):=shrinking;
  if glue_shrink(r)=0 then set_glue_ratio_zero(glue_set(r))
  else if (glue_order(r)=normal)and(height(r)-t>glue_shrink(r)) then
    set_glue_ratio_one(glue_set(r))
  else glue_set(r):=unfloat((height(r)-t)/glue_shrink(r));
  end;
height(r):=w; type(r):=vlist_node;
end
@y
@ @<Make the unset node |r| into a |vlist_node| of height |w|...@>=
begin width(r):=width(q);
if t=height(r) then
  begin glue_sign(r):=normal; glue_order(r):=normal;
  glue_set(r):=glue_ratio_zero;
  end
else if t>height(r) then
  begin glue_sign(r):=stretching;
  if glue_stretch(r)=0 then glue_set(r):=glue_ratio_zero
  else
   glue_set(r):=glue_fix(glue_stretch(r),t-height(r),abs(glue_stretch(r)/2));
  end
else  begin glue_order(r):=glue_sign(r); glue_sign(r):=shrinking;
  if glue_shrink(r)=0 then glue_set(r):=glue_ratio_zero
  else if (glue_order(r)=normal)and(height(r)-t>glue_shrink(r)) then
    glue_set(r):=glue_ratio_one
  else
   glue_set(r):=glue_fix(glue_shrink(r),height(r)-t,abs(glue_shrink(r)/2));
  end;
height(r):=w; type(r):=vlist_node;
end
@z

@x
procedure make_accent;
var s,@!t: real; {amount of slant}
@!p,@!q,@!r:pointer; {character, box, and kern nodes}
@!f:internal_font_number; {relevant font}
@!a,@!h,@!x,@!w,@!delta:scaled; {heights and widths, as explained above}
@!i:four_quarters; {character information}
begin scan_char_num; f:=cur_font; p:=new_character(f,cur_val);
if p<>null then
  begin x:=x_height(f); s:=slant(f)/float_constant(65536);
@^real division@>
@y
procedure make_accent;
var @!s,@!t:scaled; {amount of slant}
@!p,@!q,@!r:pointer; {character, box, and kern nodes}
@!f:internal_font_number; {relevant font}
@!a,@!h,@!x,@!w,@!delta:scaled; {heights and widths, as explained above}
@!i:four_quarters; {character information}
begin scan_char_num; f:=cur_font; p:=new_character(f,cur_val);
if p<>null then
  begin x:=x_height(f); s:=slant(f);
@z

@x
@<Append the accent with appropriate kerns...@>=
begin t:=slant(f)/float_constant(65536);
@^real division@>
i:=char_info(f)(character(q));
w:=char_width(f)(i); h:=char_height(f)(height_depth(i));
if h<>x then {the accent must be shifted up or down}
  begin p:=hpack(p,natural); shift_amount(p):=x-h;
  end;
delta:=round((w-a)/float_constant(2)+h*t-x*s);
@^real multiplication@>
@^real addition@>
@y
@<Append the accent with appropriate kerns...@>=
begin t:=slant(f);
i:=char_info(f)(character(q));
w:=char_width(f)(i); h:=char_height(f)(height_depth(i));
if h<>x then {the accent must be shifted up or down}
  begin p:=hpack(p,natural); shift_amount(p):=x-h;
  end;
delta:=x_over_n(w-a,2)+xn_over_d(h,t,unity)-xn_over_d(x,s,unity);
@z