Optimize string_quote() for speed

* util.c (string_quote): Speed up check for terminating NUL.
Replace strintf() with open-coded binary to hex/oct conversions -
we potentially do them for every single byte, need to be fast.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>

diff --git a/util.c b/util.c
index b2bf3e36bd451cdb4cf6fd725445e8d8f5f16463..7bf2698404f3e6d87bb16fa302c8fb3a9d635356 100644 (file)
--- a/util.c
+++ b/util.c
@@ -440,8 +440,15 @@ string_quote(const char *instr, char *outstr, int len, int size)
 {
        const unsigned char *ustr = (const unsigned char *) instr;
        char *s = outstr;
-       int usehex = 0, c, i;
+       int usehex, c, i, eol;
 
+       eol = 0x100; /* this can never match a char */
+       if (len < 0) {
+               size--;
+               eol = '\0';
+       }
+
+       usehex = 0;
        if (xflag > 1)
                usehex = 1;
        else if (xflag) {
@@ -450,13 +457,8 @@ string_quote(const char *instr, char *outstr, int len, int size)
                for (i = 0; i < size; ++i) {
                        c = ustr[i];
                        /* Check for NUL-terminated string. */
-                       if (len < 0) {
-                               if (c == '\0')
-                                       break;
-                               /* Quote at most size - 1 bytes. */
-                               if (i == size - 1)
-                                       continue;
-                       }
+                       if (c == eol)
+                               break;
                        if (!isprint(c) && !isspace(c)) {
                                usehex = 1;
                                break;
@@ -471,27 +473,19 @@ string_quote(const char *instr, char *outstr, int len, int size)
                for (i = 0; i < size; ++i) {
                        c = ustr[i];
                        /* Check for NUL-terminated string. */
-                       if (len < 0) {
-                               if (c == '\0')
-                                       break;
-                               /* Quote at most size - 1 bytes. */
-                               if (i == size - 1)
-                                       continue;
-                       }
-                       sprintf(s, "\\x%02x", c);
-                       s += 4;
+                       if (c == eol)
+                               goto asciz_ended;
+                       *s++ = '\\';
+                       *s++ = 'x';
+                       *s++ = "0123456789abcdef"[c >> 4];
+                       *s++ = "0123456789abcdef"[c & 0xf];
                }
        } else {
                for (i = 0; i < size; ++i) {
                        c = ustr[i];
                        /* Check for NUL-terminated string. */
-                       if (len < 0) {
-                               if (c == '\0')
-                                       break;
-                               /* Quote at most size - 1 bytes. */
-                               if (i == size - 1)
-                                       continue;
-                       }
+                       if (c == eol)
+                               goto asciz_ended;
                        switch (c) {
                                case '\"': case '\\':
                                        *s++ = '\\';
@@ -520,13 +514,25 @@ string_quote(const char *instr, char *outstr, int len, int size)
                                default:
                                        if (isprint(c))
                                                *s++ = c;
-                                       else if (i + 1 < size
-                                                && isdigit(ustr[i + 1])) {
-                                               sprintf(s, "\\%03o", c);
-                                               s += 4;
-                                       } else {
-                                               sprintf(s, "\\%o", c);
-                                               s += strlen(s);
+                                       else {
+                                               /* Print \octal */
+                                               *s++ = '\\';
+                                               if (i + 1 < size
+                                                   && ustr[i + 1] >= '0'
+                                                   && ustr[i + 1] <= '9'
+                                               ) {
+                                                       /* Print \ooo */
+                                                       *s++ = '0' + (c >> 6);
+                                                       *s++ = '0' + ((c >> 3) & 0x7);
+                                               } else {
+                                                       /* Print \[[o]o]o */
+                                                       if ((c >> 3) != 0) {
+                                                               if ((c >> 6) != 0)
+                                                                       *s++ = '0' + (c >> 6);
+                                                               *s++ = '0' + ((c >> 3) & 0x7);
+                                                       }
+                                               }
+                                               *s++ = '0' + (c & 0x7);
                                        }
                                        break;
                        }
@@ -536,8 +542,21 @@ string_quote(const char *instr, char *outstr, int len, int size)
        *s++ = '\"';
        *s = '\0';
 
-       /* Return nonzero if the string was unterminated.  */
-       return i == size;
+       /* Return zero if we printed entire ASCIZ string (didn't truncate it) */
+       if (len < 0 && ustr[i] == '\0') {
+               /* We didn't see NUL yet (otherwise we'd jump to 'asciz_ended')
+                * but next char is NUL.
+                */
+               return 0;
+       }
+
+       return 1;
+
+ asciz_ended:
+       *s++ = '\"';
+       *s = '\0';
+       /* Return zero: we printed entire ASCIZ string (didn't truncate it) */
+       return 0;
 }
 
 /*