Avoid unnecessary string traversals in u8_isutf() and substr().

For u8_isutf() the conditionals already ensure that a NUL byte won't
match.  For substr() we can use the byte offset of 'm' to avoid
re-scanning the initial part of the string.  From Jonas Bechtel.

diff --git a/usr.bin/awk/run.c b/usr.bin/awk/run.c
index 23bf3a9..778477d 100644 (file)
--- a/usr.bin/awk/run.c
+++ b/usr.bin/awk/run.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: run.c,v 1.87 2024/06/03 00:55:05 millert Exp $        */
+/*     $OpenBSD: run.c,v 1.88 2024/06/04 14:40:46 millert Exp $        */
 /****************************************************************
 Copyright (C) Lucent Technologies 1997
 All Rights Reserved
@@ -602,20 +602,18 @@ Cell *intest(Node **a, int n)     /* a[0] is index (list), a[1] is symtab */
 /* return length 1..4 if yes, 0 if no */
 static int u8_isutf(const char *s)
 {
-       int n, ret;
+       int ret;
        unsigned char c;
 
        c = s[0];
-       if (c < 128 || awk_mb_cur_max == 1)
-               return 1; /* what if it's 0? */
-
-       n = strlen(s);
-       if (n >= 2 && ((c>>5) & 0x7) == 0x6 && (s[1] & 0xC0) == 0x80) {
+       if (c < 128 || awk_mb_cur_max == 1) {
+               ret = 1; /* what if it's 0? */
+       } else if (((c>>5) & 0x7) == 0x6 && (s[1] & 0xC0) == 0x80) {
                ret = 2; /* 110xxxxx 10xxxxxx */
-       } else if (n >= 3 && ((c>>4) & 0xF) == 0xE && (s[1] & 0xC0) == 0x80
+       } else if (((c>>4) & 0xF) == 0xE && (s[1] & 0xC0) == 0x80
                         && (s[2] & 0xC0) == 0x80) {
                ret = 3; /* 1110xxxx 10xxxxxx 10xxxxxx */
-       } else if (n >= 4 && ((c>>3) & 0x1F) == 0x1E && (s[1] & 0xC0) == 0x80
+       } else if (((c>>3) & 0x1F) == 0x1E && (s[1] & 0xC0) == 0x80
                         && (s[2] & 0xC0) == 0x80 && (s[3] & 0xC0) == 0x80) {
                ret = 4; /* 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx */
        } else {
@@ -1018,7 +1016,7 @@ Cell *substr(Node **a, int nnn)           /* substr(a[0], a[1], a[2]) */
        DPRINTF("substr: m=%d, n=%d, s=%s\n", m, n, s);
        y = gettemp();
        mb = u8_char2byte(s, m-1); /* byte offset of start char in s */
-       nb = u8_char2byte(s, m-1+n);  /* byte offset of end+1 char in s */
+       nb = mb + u8_char2byte(&s[mb], n);  /* byte offset of end+1 char in s */
 
        temp = s[nb];   /* with thanks to John Linderman */
        s[nb] = '\0';