322 lines
11 KiB
ReStructuredText
322 lines
11 KiB
ReStructuredText
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Write You a Forth, 0x06
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-----------------------
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:date: 2018-02-28 22:55
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:tags: wyaf, forth
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Lots of updates last night; SLOC-wise, I added a bunch of new definitions:
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+ ``DEPTH``, ``.`` and ``.S`` to inspect the stack
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+ ``/MOD``, ``*/``, and ``*/MOD``, which required adding some idea of a long
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type
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+ ``0<``, ``0=``, ``0>``, ``<``, ``=``, and ``>`` for conditionals
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+ ``DUP`` and ``?DUP``
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+ the logical operators ``AND``, ``OR``, and ``NEGATE``
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+ ``ABS``
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+ ``BYE`` moved from an interpreter hack to a defined word
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+ ``D+`` and ``D-`` started me off on the concept of double numbers
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+ ``DROP``, ``OVER``, and ``ROLL`` are more stack manipulation functions
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It's starting to feel a lot like a Forth...
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Speaking of SLOC, for shits and grins I decided to see how the code base has
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grown:
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+-----------+---------------+--------+----------------------+---------------+
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| revision | lines of code | growth | focus | exec size (b) |
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+-----------+---------------+--------+----------------------+---------------+
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| 0x02 | 133 | n/a | starting point | 38368 |
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+-----------+---------------+--------+----------------------+---------------+
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| 0x03 | 245 | 1.8x | parsing | 40920 |
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+-----------+---------------+--------+----------------------+---------------+
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| 0x04 | 369 | 1.5x | stack / numerics | 48736 |
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+-----------+---------------+--------+----------------------+---------------+
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| 0x05 | 677 | 1.8x | initial dictionary | 62896 |
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+-----------+---------------+--------+----------------------+---------------+
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| 0x06 | 1436 | 2.1x | expanding vocabulary | 85256 |
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+-----------+---------------+--------+----------------------+---------------+
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Note that the executable is compiled with ``-O0 -g`` on the
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``x86_64-linux-gnu`` target.
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It makes sense that expanding the vocabulary is going to be a huge code
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expansion. I did do more than that; so, I'm not really going to show most of
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the work I did for the new words (a lot of it is repetative and mechanical).
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System updates
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^^^^^^^^^^^^^^
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Before I started expanding the dictionary, though, I made some changes to
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the ``System``::
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$ git diff HEAD^ system.h
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diff --git a/system.h b/system.h
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index 00f4a34..91aa1fa 100644
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--- a/system.h
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+++ b/system.h
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@@ -5,11 +5,24 @@
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#include "io.h"
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#include "stack.h"
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+typedef enum _SYS_STATUS : uint8_t {
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+ STATUS_OK = 0,
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+ STATUS_STACK_OVERFLOW = 1,
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+ STATUS_STACK_UNDERFLOW = 2,
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+ STATUS_EXECUTION_FAILURE = 3,
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+ STATUS_UNKNOWN_WORD = 4
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+} SYS_STATUS;
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+
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+class Word;
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+
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typedef struct _System {
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Stack<KF_INT> dstack;
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IO *interface;
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- struct Word *dict;
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+ Word *dict;
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+ SYS_STATUS status;
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} System;
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+void system_clear_error(System *sys);
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+void system_write_status(System *sys);
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#endif // __KF_CORE_H__
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\ No newline at end of file
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I've started adding a notion of system state, which I've deliberately kept
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separate from the parser state. The new functions aren't particularly
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interesting; they just write a string to the ``interface`` field so you
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get things like::
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$ ./kforth
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kforth interpreter
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? swap
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stack underflow (error code 2).
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? what-word?
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unknown word (error code 4).
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? 2
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ok.
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Note that this is separate from the parser errors::
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$ ./kforth
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kforth interpreter
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? AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
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ok.
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parse error: token too long
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? unknown word (error code 4).
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?
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Though this test does show that the interpreter could be made more robust.
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I/O updates
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^^^^^^^^^^^
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The next thing I did was move the ``write_dstack`` function into ``io.cc``;
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this is needed to implement ``.S``. While I was at it, I decided to make
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``write_num`` finally work well and correctly, and I think I've got the final
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version done::
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void
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write_num(IO *interface, KF_INT n)
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{
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char buf[nbuflen];
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uint8_t i = nbuflen - 1;
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memset(buf, 0, nbuflen);
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if (n < 0) {
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interface->wrch('-');
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}
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I'm still not proud of this hack, but it seems to be the best way to deal with
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this right now::
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else if (n == 0) {
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interface->wrch('0');
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return;
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}
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while (n != 0) {
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char x = n % 10;
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This was the magic that finally got it right: negating the digits as they're
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going into the buffer. No more trying to invert the whole number, just each
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digit::
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x = x < 0 ? -x : x;
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x += '0';
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buf[i--] = x;
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n /= 10;
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}
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interface->wrbuf(buf+i, nbuflen - i);
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}
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My first pass at this wrote the string forwards, then reversed it. I didn't
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like that; while performance isn't my first concern, it just seemed like a
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fun challenge to get the reversed buffer written correctly.
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While I was in the I/O subsystem, I also decided to update the ``IO`` base
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class to include a ``newline`` method; I had a few instances of
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``interface->wrch('\n')`` sprinkled throughout, but that won't necessarily be
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correct elsewhere.
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Miscellaneous updates
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^^^^^^^^^^^^^^^^^^^^^^
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I add a new definition to the ``defs.h`` files: a ``KF_LONG`` type to prepare
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for the double numbers mentioned in the next section, and switched to static
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compilation.
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New words!
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^^^^^^^^^^
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Finally, I started adding the new words in. I'm still trying to figure out a
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good way to handle the address types (I think I'll just introduce a ``KF_ADDR``
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type) so I've punted on those for now.
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.. _pforth: http://www.softsynth.com/pforth/
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.. _gforth: https://www.gnu.org/software/gforth/
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One of the interesting challenges is dealing with the double numbers. These are
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on the stack as a pair of smaller numbers, e.g. if the double number type is 64
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bits and the standard number type is 32 bits, then you might see something like
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this (via pforth_)::
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0 1 0 1 D+
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ok
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Stack<10> 0 2
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So, how to deal with this? There's a ``D.`` word, which I don't have
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implemented yet, that will let me see what pforth_ and gforth_ do::
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$ pforth -q
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Begin AUTO.INIT ------
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0 1 D. 1 0 D.
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4294967296 1
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^C
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$ gforth
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Gforth 0.7.2, Copyright (C) 1995-2008 Free Software Foundation, Inc.
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Gforth comes with ABSOLUTELY NO WARRANTY; for details type `license'
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Type `bye' to exit
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0 1 D. 1 0 D. 18446744073709551616 1 ok
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So, it looks like the first number on the stack is the low part, and the second
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is the high part. This is, once again, pretty straightforward: I'll need to
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shift the first number by the appropriate number of bits and then add the
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second number to it.
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constexpr size_t dshift = (sizeof(KF_INT) * 8) - 1;
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static bool
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pop_long(System *sys, KF_LONG *d)
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{
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KF_INT a = 0;
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KF_INT b = 0;
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if (!sys->dstack.pop(&a)) {
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sys->status = STATUS_STACK_UNDERFLOW;
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return false;
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}
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if (!sys->dstack.pop(&b)) {
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sys->status = STATUS_STACK_UNDERFLOW;
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return false;
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}
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*d = static_cast<KF_LONG>(a) << dshift;
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*d += static_cast<KF_LONG>(b);
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sys->status = STATUS_OK;
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return true;
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}
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This function also shows off the new status work and how that turns out. I've
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kept the exec interface as a boolean to indicate success or failure.
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To push the results back onto the stack, I needed to first write a masking
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function to make sure to clear out any lingering bits::
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static inline KF_INT
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mask(size_t bits)
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{
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KF_INT m = 0;
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for (size_t i = 0; i < bits; i++) {
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m += 1 << i;
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}
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return m;
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}
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I should probably check `Hacker's Delight <http://hackersdelight.org/>`_ to see
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if there's any tricks for this.
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With the mask available, getting a long into a pair of ints requires shifting
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and clearing for the high part and clearing for the low part::
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static bool
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push_long(System *sys, KF_LONG d)
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{
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KF_INT a = static_cast<KF_INT>((d >> dshift) & mask(dshift));
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KF_INT b = static_cast<KF_INT>(d & mask(dshift));
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if (!sys->dstack.push(b)) {
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sys->status = STATUS_STACK_OVERFLOW;
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return false;
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}
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if (!sys->dstack.push(a)) {
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sys->status = STATUS_STACK_OVERFLOW;
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return false;
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}
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sys->status = STATUS_OK;
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return true;
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}
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One of the words that interacts with doubles is ``D+``::
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static bool
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dplus(System *sys)
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{
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KF_LONG da, db;
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if (!pop_long(sys, &da)) {
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// Status is already set.
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return false;
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}
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if (!pop_long(sys, &db)) {
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// Status is already set.
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return false;
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}
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da += db;
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if (!push_long(sys, da)) {
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// Status is already set.
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return false;
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}
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// Status is already set.
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return true;
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}
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The only other thing I really did was to add a ``remove`` method to the Stack
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class to support ``ROLL``.
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Huge diff, but not as much to say about it --- next up, I think I'm going to
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introduce the ``KF_ADDR`` type and start working on some of the address
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interaction stuff. I'll also add more of the double number words, too. The
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words I still have to implement from the `FORTH-83 standard`_ nuclear layer
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are:
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+ ``!``, ``+!``, ``@``, ``C!``, ``C@``, ``CMOVE``, ``CMOVE>``, ``COUNT``,
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``FILL``: memory manipulation words
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+ ``DNEGATE``, ``MAX``, ``MIN``, ``MOD``, ``XOR``: more arithmetic words
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+ ``EXECUTE``, ``EXIT``, ``I``, ``J``, ``PICK``: various words
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+ ``>R``, ``R>``, ``R@``: return stack words
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+ ``U<``, ``UM*``, ``UM/MOD``: unsigned math words
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.. _FORTH-83 standard: http://forth.sourceforge.net/standard/fst83/fst83-12.htm
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As before, the snapshot for this update is tagged `part-0x06
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<https://github.com/kisom/kforth/tree/part-0x06>`_.
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