Format/typo check + update bugs.md for 1992/vern

The bugs.md has both a feature and a bug or maybe mis-feature that might
be good to fix. I gave a tip in the bugs.md that might help with parsing
the code a bit.

The README.md file has been typo and format checked/fixed.

This should complete 1992.
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Cody Boone Ferguson committed 2023-11-09 08:18:09 -08:00
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@@ -5,6 +5,19 @@ make all
```
### Bugs and (Mis)features:
The current status of this entry is:
```
STATUS: known bug - please help us fix
STATUS: INABIAF - please **DO NOT** fix
```
For more detailed information see [1992 vern in bugs.md](/bugs.md#1992-vern).
## To use:
```sh
@@ -46,15 +59,15 @@ a slightly modified version with shorter lines has been provided.
## Author's remarks:
This program plays chess. You play the white pieces and the program
the black pieces. Moves are entered as a two-digit number specifying
the coordinates of the piece to be moved followed by another two-digit
number specifying the coordinates of where to move it. Rows and
columns are numbered starting with (0,0) for the upper-left-hand corner
(black's queen's rook) and going to (7,7) for the lower-right-hand
corner (white's king's rook). For example, the PK4 opening for white
is indicated as "64 44". Moves are read using `scanf()` so care should
be taken to not enter the wrong number of fields.
This program plays chess. You play the white pieces and the program the black
pieces. Moves are entered as a two-digit number specifying the coordinates of
the piece to be moved followed by another two-digit number specifying the
coordinates of where to move it. Rows and columns are numbered starting with
`(0,0)` for the upper-left-hand corner (black's queen's rook) and going to
`(7,7)` for the lower-right-hand corner (white's king's rook). For example, the
`PK4` opening for white is indicated as `"64 44" (without the quotes)`. Moves
are read using `scanf()` so care should be taken to not enter the wrong number
of fields.
If the move you enter is illegal then you are just prompted again to
move. If the move is legal then the new position is displayed and the
@@ -62,14 +75,14 @@ program starts computing its response. For every 64 board positions it
examines a "." is printed. Once it has chosen its move it simply
displays the board updated to reflect the move.
Your move is prompted for using a string like "1351 9 2 >". The first
Your move is prompted for using a string like `"1351 9 2 >"`. The first
number is how many board positions the program examined when computing
its previous response. The second number is its anticipated value for
the move it just made (with larger numbers meaning an ultimately better
board position for it), and the third number is the evaluation it
assigns to the your current position (larger numbers meaning better
positions for you). A ">" indicates that you are not in check; for
check it is changed to "!".
positions for you). A `>` indicates that you are not in check; for
check it is changed to `!`.
There are a few limitations on play:
@@ -89,17 +102,16 @@ recognized per se, but when selecting its move the program assigns a
stalemate position a value of 0 so it will try for a stalemate if its
other options are worse.
The program takes one optional argument indicating the ply (lookahead)
it should use. The default is 2, which is enough to keep it from
making flaming blunders. The higher the ply, the better the play, and
the longer you have to wait. For example, at a ply of 2, a response to
the PK4 opening takes about 1.8 CPU seconds on a SPARC ELC when
compiled -O with Sun cc. A ply of 3 takes 13 CPU seconds (and results
in a different response to PK4) and a ply of 4 takes a little under 4
CPU minutes (and for PK4 comes up with the same response as a ply of
3). A ply of 3 is in general good enough to avoid not only flaming
blunders but also immediately stupid moves altogether. A ply of 4
will find all mate-in-two's.
The program takes one optional argument indicating the ply (lookahead) it should
use. The default is 2, which is enough to keep it from making flaming blunders.
The higher the ply, the better the play, and the longer you have to wait. For
example, at a ply of 2, a response to the `PK4` opening takes about 1.8 CPU
seconds on a SPARC ELC when compiled `-O` with Sun `cc`. A ply of 3 takes 13
CPU seconds (and results in a different response to `PK4`) and a ply of 4 takes
a little under 4 CPU minutes (and for `PK4` comes up with the same response as a
ply of 3). A ply of 3 is in general good enough to avoid not only flaming
blunders but also immediately stupid moves altogether. A ply of 4 will find all
mate-in-two's.
### Obfuscation
@@ -111,7 +123,15 @@ As can be seen from the build file, certain combinations of these
characters followed by a particular whitespace character are expanded
at build time into much-needed text. Without this hack the program
wouldn't pass the character limit. A nice side effect is that the
initial source is gloriously difficult to peruse.
initial source is gloriously difficult to peruse. In particular, the Makefile
does:
```sh
sed <vern.c 's/{ /(/g;s/} /)/g;s/; /#define /' | \
sed 's/} /=/g;s/{ /i/g' >vern.tmp.c
```
and compiles `vern.tmp.c`.
Second, the rather ho-hum step has been taking of naming each variable
with a one or two letter identifier to render it meaningless (and save
@@ -126,23 +146,23 @@ called they return 1 if the current move is illegal for that piece and
indicating the type of the piece (though the type can also be determined
by comparing the function pointer with the function itself).
Fourth, there are no independent routines for generating potential
moves. Instead, the program generates its moves by brute force: for
every piece it controls on the board, it attempts to move it to every
square on the board. Those moves that are legal it then explores to
see their effects (using alpha-beta search). This tactic somewhat
obfuscates the algorithm used by the program.
Fourth, there are no independent routines for generating potential moves.
Instead, the program generates its moves by brute force: for every piece it
controls on the board, it attempts to move it to every square on the board.
Those moves that are legal it then explores to see their effects (using
[alpha-beta search](https://en.wikipedia.org/wiki/Alpha-beta_pruning)). This
tactic somewhat obfuscates the algorithm used by the program.
Finally, there are three key constants that occur throughout the program: 64,
8, and 3 (lg 8). Rather than making these available at compile-time, which
provides a hint as to what the program is up to, they are computed
Finally, there are three key constants that occur throughout the program: `64`,
`8`, and `3` (`lg 8`). Rather than making these available at compile-time,
which provides a hint as to what the program is up to, they are computed
probabilistically at run-time. An instance of the ["Inspection
Paradox"](https://en.wikipedia.org/wiki/Renewal_theory#Inspection_paradox) is
used which happens to produce a value that on average is close to .64. 10000
instances of this value are computed, added up, and then divided by 100.
Sometimes the value produced will be 63 or 65 instead of 64 (but I've never
observed any other values), so the result is then rounded to the nearest
multiple of 4, and then the other constants are derived from it.
used which happens to produce a value that on average is close to `.64`.
`10000` instances of this value are computed, added up, and then divided by
`100`. Sometimes the value produced will be `63` or `65` instead of `64` (but
I've never observed any other values), so the result is then rounded to the
nearest multiple of `4`, and then the other constants are derived from it.
## Copyright and CC BY-SA 4.0 License: