Calling MB_CUR_MAX is much more expensive than incrementing a pointer

and than testing and printing a byte, so do it once up front rather
than inside the inner loop.  This speeds up rev(1) by about a factor
of three for typical use cases.
Performance issue found by cheloha@, but my fix is a bit simpler
and more rigorous than Scott's original patch.

While here, also add the missing handling for write errors (making
them fatal, whereas read errors remain non-fatal and proceed to the
next input file) and also avoid testing each byte twice, making the
code more straightforward and more readable.

In part using ideas from millert@ and martijn@.
OK martijn@.

diff --git a/usr.bin/rev/rev.c b/usr.bin/rev/rev.c
index 10b5148..d0d258f 100644 (file)
--- a/usr.bin/rev/rev.c
+++ b/usr.bin/rev/rev.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: rev.c,v 1.13 2016/04/10 17:06:52 martijn Exp $        */
+/*     $OpenBSD: rev.c,v 1.14 2022/01/13 05:10:46 schwarze Exp $       */
 /*     $NetBSD: rev.c,v 1.5 1995/09/28 08:49:40 tls Exp $      */
 
 /*-
@@ -46,13 +46,14 @@ void usage(void);
 int
 main(int argc, char *argv[])
 {
-       char *filename, *p = NULL, *t, *u;
+       char *filename, *p = NULL, *t, *te, *u;
        FILE *fp;
        ssize_t len;
        size_t ps = 0;
-       int ch, rval;
+       int ch, multibyte, rval;
 
        setlocale(LC_CTYPE, "");
+       multibyte = MB_CUR_MAX > 1;
 
        if (pledge("stdio rpath", NULL) == -1)
                err(1, "pledge");
@@ -83,14 +84,16 @@ main(int argc, char *argv[])
                        if (p[len - 1] == '\n')
                                --len;
                        for (t = p + len - 1; t >= p; --t) {
-                               if (isu8cont(*t))
-                                       continue;
-                               u = t;
-                               do {
-                                       putchar(*u);
-                               } while (isu8cont(*(++u)));
+                               te = t;
+                               if (multibyte)
+                                       while (t > p && isu8cont(*t))
+                                               --t;
+                               for (u = t; u <= te; ++u)
+                                       if (putchar(*u) == EOF)
+                                               err(1, "stdout");
                        }
-                       putchar('\n');
+                       if (putchar('\n') == EOF)
+                               err(1, "stdout");
                }
                if (ferror(fp)) {
                        warn("%s", filename);
@@ -104,7 +107,7 @@ main(int argc, char *argv[])
 int
 isu8cont(unsigned char c)
 {
-       return MB_CUR_MAX > 1 && (c & (0x80 | 0x40)) == 0x80;
+       return (c & (0x80 | 0x40)) == 0x80;
 }
 
 void