@c 
@c This file contains changes to the K Technical Manual since 7/12/88
@c editors-note-7-12.botex contains changes to the manual previous to 7/12/88
@c
@chapter Editor's Note
@sp 2
This draft of the @b[K Technical Manual] contains the
following revisions (in cases where there are discrepancies in
chapter/section numbers between drafts, those of the current draft are
used).

@sp 2
@group
@center @b[9.1 Organization]
@sp 1
@i[Entire section has been revised and reworded.]
@end group
@sp 1
@b[9.1 Organization]
@sp 1
The visible features of the call hardware include the @i[call stack],
and the @i[free frame heap].

The call stack is used to save and restore processor state during
function call operations. Each entry on the call stack represents, at
least conceptually, the Lisp Machine idea of a stack frame.  When a
function is called, an entry is pushed to save the state of the caller;
when a function returns, an entry is popped to re-establish the state of
the caller.

The free frame heap maintains a hardware list of unused register frames.
The heap hardware is also responsible for causing a ``yellow alert''
trap (by asserting TRAP_STACK_OVF) whenever the call hardware allocates
more than a pre-established number of frames.  This trap is used to
trigger the copying of the call stack to memory; the copied frames are
then available for immediate use.

The hardware does not cause a trap when a call stack 
@i[underflow] is about to occur.  Software
must set up the Return PC at the base
of the call hardware stack with the address of a special routine, which 
must:

@itemize @bullet
@item
read in the top section of the call stack from memory;
@item 
branch to the Return PC of the routine whose frame was found at the base 
of the hardware stack.
@end itemize

@sp 2
@group
@center @b[19.3.2 Bignums]
@sp 1
@i[Byte specifier diagram for bignums has been modified to indicate that only the low-order 18 
bits are relevant for the Number of Data Words pointer.]
@end group
@sp 1
@b[19.3.2 Bignums]

@tex
Bignums may use up to $2^{18}$ words of storage for a number.
The range of bignums is $-2^{2^{23}}$ to $2^{2^{23}} - 1$.  However, a
bignum may not have a value in the fixnum range ($-2^{23}$ to $2^{23} - 1$).
If the result of a bignum operation lies in that range, it must be converted
to a fixnum.
@end tex

@group
@tex
\startbyf
\bif{32}    {1}
\byf{31}{26}{000100}
\byf{25}{ 0}{Pointer (P)}
\endbyf
\line{\hfil\byfnumbers}
\line{\hfil\byfbox}
\vskip 0.2in

\startbyf
\byf{31}{26}{100000}
\byf{25}{19}{Unknown}
\byf{18}{ 0}{Number of data words (N)}
\endbyf
\line{\hfil\byfnumbers}
\line{\hfil$P\rightarrow$\byfbox}

\startbyf
\byf{31}{ 0}{Least Significant Word}
\endbyf
\line{\hfil$P+1\rightarrow$\byfbox}

\startbyf
\byf{31}{ 0}{Middle Words $\ldots$}
\endbyf
\line{\hfil$\ldots$\byfbox}

\startbyf
\byf{31}{ 0}{Most Significant Word}
\endbyf
\line{\hfil$P+N\rightarrow$\byfbox}
@end tex
@end group


@sp 2
@group
@center @b[19.7.4.2 Fill Pointer]
@sp 1
@i[Clarification to text:]
@end group
@sp 1
@b[19.7.4.2 Fill Pointer]

The fill pointer is a fixnum that indicates the number of
words currently used in an array. If present, it is the first 
leader word.



@sp 2
@group
@center @b[19.7.4.4 Leaders]
@sp 1
@i[Clarification to text:]
@end group
@sp 1
@b[19.7.4.4 Leaders ]

If the has leader bit is set then the array has an array leader. The
offset from the main header to the "Number Of Leader Words" word is in the
leader-offset field.



@sp 2
@group
@center @b[19.8 Compiled Functions]
@sp 1
@i[Change to byte specifier abbreviation of word pointed at by instruction P+6,
to "CP":]
@end group
@sp 1
@group
.

.

.

@tex
\startbyf
\byf{31}{26}{Data Type}
\byf{25}{ 0}{Compiled Function Code Pointer (CP)}
\endbyf
\line{\hfil$P+6\rightarrow$\byfbox}
@end tex
.

.

.

@end group
@sp 8
@group
Future drafts of the @b[K Technical Manual] will incorporate further revisions to this document.
@sp 2
@flushright
@b[---David Saslav]
@end flushright
@end group