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get_rnd_text() for rumors and other stuff

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Solve the uneven distribution situation that has been present for
picking random rumors for a long time and for random engravings,
epitaphs, and hallucinatory monster names since 3.6.0.  This relies
on the previous partial solution where short lines have been padded
to a longer length.  When that length is N and random seek lands in
a long line of length L, retry if the position is in the first L-N
characters.  Put differently, it if takes more than N characters to
reach the next newline, reject that random seek and try again.  This
effectively makes long lines behave as if they had the same length
of N as the short lines have been padded to and when all lines are
the same length, all entries have the same chance to be chosen.
This commit is contained in:
PatR
2021-11-27 12:23:01 -08:00
parent 629c2c4094
commit 03476a7c78
7 changed files with 50 additions and 32 deletions
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2
doc/fixes37.0
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@@ -701,6 +701,8 @@ selection of random engravings, epitaphs, and hallucinatory monster names had
ones which follow shorter than average lines are least likely; use
same workaround as for rumors: pad the shortest lines; result isn't
uniforn distribution but is better (tradeoff vs size; see makedefs)
make selection of random rumors, engravings, epitaphs, and hallucinatory monst
names have uniform distribution by handling long lines specially
Fixes to 3.7.0-x Problems that Were Exposed Via git Repository

2
include/extern.h
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@@ -2263,7 +2263,7 @@ extern const char *Goodbye(void);
/* ### rumors.c ### */
extern char *getrumor(int, char *, boolean);
extern char *get_rnd_text(const char *, char *, int(*)(int));
extern char *get_rnd_text(const char *, char *, int(*)(int), unsigned);
extern void outrumor(int, int);
extern void outoracle(boolean, boolean);
extern void save_oracles(NHFILE *);

11
include/global.h
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@@ -9,7 +9,8 @@
#include <stdio.h>
/*
* Files expected to exist in the playground directory.
* Files expected to exist in the playground directory (possibly inside
* a dlb container file).
*/
#define RECORD "record" /* file containing list of topscorers */
@@ -32,6 +33,14 @@
#define TRIBUTEFILE "tribute" /* 3.6 tribute to Terry Pratchett */
#define LEV_EXT ".lua" /* extension for special level files */
/* padding amounts for files that have lines chosen by fseek to random spot,
advancing to the next line, and using that line; makedefs forces shorter
lines to be padded to these lengths; value of 0 will inhibit any padding,
avoiding an increase in files' sizes, but resulting in biased selection;
used by makedefs while building and by core's callers of get_rnd_text() */
#define MD_PAD_RUMORS 60u /* for RUMORFILE, EPITAPHFILE, and ENGRAVEFILE */
#define MD_PAD_BOGONS 20u /* for BOGUSMONFILE */
/* Assorted definitions that may depend on selections in config.h. */
/*

2
src/do_name.c
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@@ -2204,7 +2204,7 @@ bogusmon(char *buf, char *code)
if (code)
*code = '\0';
/* might fail (return empty buf[]) if the file isn't available */
get_rnd_text(BOGUSMONFILE, buf, rn2_on_display_rng);
get_rnd_text(BOGUSMONFILE, buf, rn2_on_display_rng, MD_PAD_BOGONS);
if (!*mnam) {
Strcpy(buf, "bogon");
} else if (index(bogon_codes, *mnam)) { /* strip prefix if present */

4
src/engrave.c
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@@ -18,7 +18,7 @@ random_engraving(char *outbuf)
/* a random engraving may come from the "rumors" file,
or from the "engrave" file (formerly in an array here) */
if (!rn2(4) || !(rumor = getrumor(0, outbuf, TRUE)) || !*rumor)
(void) get_rnd_text(ENGRAVEFILE, outbuf, rn2);
(void) get_rnd_text(ENGRAVEFILE, outbuf, rn2, MD_PAD_RUMORS);
wipeout_text(outbuf, (int) (strlen(outbuf) / 4), 0);
return outbuf;
@@ -1446,7 +1446,7 @@ make_grave(int x, int y, const char *str)
/* Engrave the headstone */
del_engr_at(x, y);
if (!str)
str = get_rnd_text(EPITAPHFILE, buf, rn2);
str = get_rnd_text(EPITAPHFILE, buf, rn2, MD_PAD_RUMORS);
make_engr_at(x, y, str, 0L, HEADSTONE);
return;
}

34
src/rumors.c
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@@ -395,7 +395,11 @@ RESTORE_WARNING_FORMAT_NONLITERAL
/* Gets a random line of text from file 'fname', and returns it.
rng is the random number generator to use, and should act like rn2 does. */
char *
get_rnd_text(const char* fname, char* buf, int (*rng)(int))
get_rnd_text(
const char *fname,
char *buf,
int (*rng)(int),
unsigned padlength)
{
dlb *fh;
@@ -404,6 +408,7 @@ get_rnd_text(const char* fname, char* buf, int (*rng)(int))
if (fh) {
/* TODO: cache sizetxt, starttxt, endtxt. maybe cache file contents? */
long sizetxt = 0L, starttxt = 0L, endtxt = 0L, tidbit = 0L;
int trylimit;
char *endp, line[BUFSZ], xbuf[BUFSZ];
/* skip "don't edit" comment */
@@ -419,14 +424,29 @@ get_rnd_text(const char* fname, char* buf, int (*rng)(int))
that save and restore might fix the problem wouldn't be useful */
if (sizetxt < 1L)
return buf;
tidbit = (*rng)(sizetxt);
/* 'rumors' is about 3/4 of the way to the limit on a 16-bit config */
nhassert(sizetxt <= INT_MAX); /* essential for rn2(sizetxt) */
/* position randomly which will probably be in the middle of a line;
read the rest of that line, then use the next one; if there's no
next one (ie, end of file), go back to beginning and use first */
(void) dlb_fseek(fh, starttxt + tidbit, SEEK_SET);
(void) dlb_fgets(line, sizeof line, fh);
/*
* Position randomly which will probably be in the middle of a line.
* Read the rest of that line, then use the next one. If there's no
* next line (ie, end of file), go back to beginning and use first.
*
* When short lines have been padded to length N, only accept long
* lines if we land within last N+1 characters (+1 is for newline
* which hasn't been stripped away yet), effectively shortening
* them to normal length. That yields even selection distribution.
*/
for (trylimit = 5; trylimit > 0; --trylimit) {
tidbit = (long) (*rng)((int) sizetxt);
(void) dlb_fseek(fh, starttxt + tidbit, SEEK_SET);
(void) dlb_fgets(line, sizeof line, fh);
if (!padlength || (unsigned) strlen(line) <= padlength + 1)
break;
}
/* use next line */
if (!dlb_fgets(line, sizeof line, fh)) {
/* assume failure is due to end-of-file; go back to start */
(void) dlb_fseek(fh, starttxt, SEEK_SET);
(void) dlb_fgets(line, sizeof line, fh);
}

27
util/makedefs.c
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@@ -104,21 +104,6 @@ static const char SCCS_Id[] UNUSED = "@(#)makedefs.c\t3.7\t2020/01/18";
#endif /* else !MAC */
#endif /* else !AMIGA */
/*
* For files where entries are selected by seeking to a random position,
* skipping to newline, and then using the next line, lines that follow
* long ones are more likely to be selected than average and lines that
* follow short ones are less likely to be selected than average.
* We make selection be more evenly distributed by padding the shortest
* lines, at the cost of making the data files bigger. The larger these
* values are, the more uniform the selection will become but the more
* space will be needed for data used for something which is relatively
* inconsequential to actual game play. A value of 0 would suppress the
* padding because every line is already at least that long.
*/
#define PAD_RUMORS_TO 60u /* also used for epitaphs and engravings */
#define PAD_BOGONS_TO 20u /* hallucinatory monsters */
static const char
*Dont_Edit_Code =
"/* This source file is generated by 'makedefs'. Do not edit. */\n",
@@ -329,16 +314,16 @@ do_makedefs(char *options)
do_rnd_access_file(EPITAPHFILE,
/* default epitaph: parody of the default engraving */
"No matter where I went, here I am.",
PAD_RUMORS_TO);
MD_PAD_RUMORS); /* '_RUMORS' is correct here */
do_rnd_access_file(ENGRAVEFILE,
/* default engraving: popularized by "The Adventures of
Buckaroo Bonzai Across the 8th Dimenstion" but predates
that 1984 movie; some attribute it to Confucius */
"No matter where you go, there you are.",
PAD_RUMORS_TO);
MD_PAD_RUMORS); /* '_RUMORS' used here too */
do_rnd_access_file(BOGUSMONFILE,
/* default bogusmon: iconic monster that isn't in nethack */
"grue", PAD_BOGONS_TO);
"grue", MD_PAD_BOGONS);
break;
case 'h':
case 'H':
@@ -896,6 +881,8 @@ padline(char *line, unsigned padlength)
* follow short-line rumors are least likely to be chosen.
* We ameliorate the latter by padding the shortest lines,
* increasing the chance of the random seek landing in them.
* The core's get_rnd_text() handles long lines in a way
* that results in even selection distribution.
*
* Random epitaphs, engravings, and hallucinatory monster
* names are in the same boat.
@@ -1059,13 +1046,13 @@ do_rumors(void)
false_rumor_offset = read_rumors_file(".tru", &true_rumor_count,
&true_rumor_size, true_rumor_offset,
PAD_RUMORS_TO);
MD_PAD_RUMORS);
if (!false_rumor_offset)
goto rumors_failure;
eof_offset = read_rumors_file(".fal", &false_rumor_count,
&false_rumor_size, false_rumor_offset,
PAD_RUMORS_TO);
MD_PAD_RUMORS);
if (!eof_offset)
goto rumors_failure;