Module Name: src
Committed By: dholland
Date: Sun Aug 11 00:48:37 UTC 2013
Modified Files:
src/usr.bin/tr: tr.c
Log Message:
Add comments explaining how this works.
To generate a diff of this commit:
cvs rdiff -u -r1.17 -r1.18 src/usr.bin/tr/tr.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/usr.bin/tr/tr.c
diff -u src/usr.bin/tr/tr.c:1.17 src/usr.bin/tr/tr.c:1.18
--- src/usr.bin/tr/tr.c:1.17 Sun Aug 11 00:39:22 2013
+++ src/usr.bin/tr/tr.c Sun Aug 11 00:48:37 2013
@@ -1,4 +1,4 @@
-/* $NetBSD: tr.c,v 1.17 2013/08/11 00:39:22 dholland Exp $ */
+/* $NetBSD: tr.c,v 1.18 2013/08/11 00:48:37 dholland Exp $ */
/*
* Copyright (c) 1988, 1993
@@ -39,7 +39,7 @@ __COPYRIGHT("@(#) Copyright (c) 1988, 19
#if 0
static char sccsid[] = "@(#)tr.c 8.2 (Berkeley) 5/4/95";
#endif
-__RCSID("$NetBSD: tr.c,v 1.17 2013/08/11 00:39:22 dholland Exp $");
+__RCSID("$NetBSD: tr.c,v 1.18 2013/08/11 00:48:37 dholland Exp $");
#endif /* not lint */
#include <sys/types.h>
@@ -156,24 +156,48 @@ main(int argc, char **argv)
if (!isstring2)
usage();
+ /*
+ * The first and second strings need to be matched up. This
+ * means that if we are doing -c, we need to scan the first
+ * string in advance, complement it, and match *that* against
+ * the second string; otherwise we need to scan them together.
+ */
+
if (cflag) {
+ /*
+ * Scan string 1 and complement it. After this,
+ * string1[] contains 0 for chars to leave alone and 1
+ * for chars to translate.
+ */
setup(string1, argv[0], 1, cflag);
s1 = NULL; /* for safety */
+ /* we will use ch to iterate over string1, so start it */
ch = -1;
} else {
+ /* Create the scanner for string 1. */
s1 = str_create(1, argv[0]);
for (ch = 0; ch < NCHARS; ch++) {
string1[ch] = ch;
}
}
+ /* Create the scanner for string 2. */
s2 = str_create(2, argv[1]);
+ /* Read the first char of string 2 first to make sure there is one. */
if (!next(s2, &ch2))
errx(1, "empty string2");
- /* If string2 runs out of characters, use the last one specified. */
+ /*
+ * Loop over the chars from string 1. After this loop string1[]
+ * is a mapping from input to output chars.
+ */
while (1) {
if (cflag) {
+ /*
+ * Try each character in order. For characters we
+ * skip over because we aren't translating them,
+ * set the translation to the identity.
+ */
ch++;
while (ch < NCHARS && string1[ch] == 0) {
if (string1[ch] == 0) {
@@ -186,18 +210,32 @@ main(int argc, char **argv)
}
}
else {
+ /* Get the next character from string 1. */
if (!next(s1, &ch)) {
break;
}
}
+ /* Set the translation to the character from string 2. */
string1[ch] = ch2;
+
+ /* Note the characters to squeeze in string2[]. */
if (sflag) {
string2[ch2] = 1;
}
+
+ /*
+ * Get the next character from string 2. If it runs
+ * out, this will keep returning the last character
+ * over and over again.
+ */
(void)next(s2, &ch2);
}
+ /*
+ * Now do it.
+ */
+
if (sflag)
for (lastch = OOBCH; (ch = getchar()) != EOF;) {
ch = string1[ch];
@@ -210,6 +248,7 @@ main(int argc, char **argv)
while ((ch = getchar()) != EOF)
(void)putchar(string1[ch]);
+ /* Clean up and exit. */
if (s1 != NULL) {
str_destroy(s1);
}
