fnematch: fix a bug that could result in extra chars being pushed back.

From Arnold Robbins.  https://github.com/onetrueawk/awk/pull/213

diff --git a/usr.bin/awk/b.c b/usr.bin/awk/b.c
index ab0228b..543fbf7 100644 (file)
--- a/usr.bin/awk/b.c
+++ b/usr.bin/awk/b.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: b.c,v 1.46 2023/11/15 18:48:13 millert Exp $  */
+/*     $OpenBSD: b.c,v 1.47 2023/11/15 18:56:53 millert Exp $  */
 /****************************************************************
 Copyright (C) Lucent Technologies 1997
 All Rights Reserved
@@ -905,13 +905,10 @@ bool fnematch(fa *pfa, FILE *f, char **pbuf, int *pbufsize, int quantum)
                 * (except for EOF's nullbyte, if present) and null
                 * terminate the buffer.
                 */
-               do {
-                       int ii;
-                       for (ii = r.len; ii > 0; ii--)
-                               if (buf[--k] && ungetc(buf[k], f) == EOF)
-                                       FATAL("unable to ungetc '%c'", buf[k]);
-               } while (k > i + patlen);
-               buf[k] = '\0';
+               for (; r.len > 0; r.len--)
+                       if (buf[--k] && ungetc(buf[k], f) == EOF)
+                               FATAL("unable to ungetc '%c'", buf[k]);
+               buf[k-patlen] = '\0';
                return true;
        }
        else