[Qemu-devel] Re: [PATCH 01/10] Introduce qmisc module

[Anthony Liguori <anthony@codemonkey.ws>]

Paolo Bonzini wrote:
> On 10/16/2009 11:37 PM, Anthony Liguori wrote:
>>
>> I already am :-)  Stay tuned, I should have a patch later this 
>> afternoon.
>
> Was it a race?  (Seriously, sorry I didn't notice a couple of hours ago).
>
> This one is ~5% slower than the "Evil" one, but half the size.  Tested 
> against the comments.json file from the "Evil" parser and with 
> valgrind too.  Does all the funky Unicode stuff too.
>
> Paolo
> /*
>  * An event-based, asynchronous JSON parser.
>  *
>  * Copyright (C) 2009 Red Hat Inc.
>  *
>  * Authors:
>  *  Paolo Bonzini <pbonzini@redhat.com>
>  *
>  * Permission is hereby granted, free of charge, to any person obtaining a copy
>  * of this software and associated documentation files (the "Software"), to deal
>  * in the Software without restriction, including without limitation the rights
>  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
>  * copies of the Software, and to permit persons to whom the Software is
>  * furnished to do so, subject to the following conditions:
>  * 
>  * The above copyright notice and this permission notice shall be included in
>  * all copies or substantial portions of the Software.
>  *
>  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
>  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
>  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
>  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
>  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
>  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
>  * SOFTWARE.
>  */
>
>
> #include "json.h"
> #include <string.h>
> #include <stdlib.h>
>
> /* Common character classes.  */
>
> #define CASE_XDIGIT \
>         case 'a': case 'b': case 'c': case 'd': case 'e': case 'f': \
>         case 'A': case 'B': case 'C': case 'D': case 'E': case 'F'
>
> #define CASE_DIGIT \
>         case '0': case '1': case '2': case '3': case '4': \
>         case '5': case '6': case '7': case '8': case '9'
>
> /* Helper function to go from \uXXXX-encoded UTF-16 to UTF-8.  */
>
> static bool hex_to_utf8 (char *buf, char **dest, char *src)
> {
>     int i, n;
>     uint8_t *p;
>
>     for (i = n = 0; i < 4; i++) {
>         n <<= 4;
>         switch (src[i])
>         {
>         CASE_DIGIT: n |= src[i] - '0'; break;
>         CASE_XDIGIT: n |= (src[i] & ~32) - 'A' + 10; break;
>         default: return false;
>         }
>     }
>
>     p = (uint8_t *)*dest;
>     if (n < 128) {
>         *p++ = n;
>     } else if (n < 2048) {
>         *p++ = 0xC0 | (n >> 6);
>         *p++ = 0x80 | (n & 63);
>     } else if (n < 0xDC00 || n > 0xDFFF) {
>         *p++ = 0xE0 | (n >> 12);
>         *p++ = 0x80 | ((n >> 6) & 63);
>         *p++ = 0x80 | (n & 63);
>     } else {
>         /* Merge with preceding high surrogate.  */
>         if (p - (uint8_t *)buf < 3
>             || p[-3] != 0xED
>             || p[-2] < 0xA0 || p[-2] > 0xAF) /* 0xD800..0xDBFF */
>             return false;
>
>         n += 0x10000 - 0xDC00;
>         n |= ((p[-2] & 15) << 16) | ((p[-1] & 63) << 10);
>
>         /* Overwrite high surrogate.  */
>         p[-3] = 0xF0 | (n >> 18);
>         p[-2] = 0x80 | ((n >> 12) & 63);
>         p[-1] = 0x80 | ((n >> 6) & 63);
>         *p++ = 0x80 | (n & 63);
>     }
>     *dest = (char *)p;
>     return true;
> }
>
> struct json_parser {
>     struct    json_parser_config c;
>     size_t    n, alloc;
>     char      *buf;
>     size_t    sp;
>     uint32_t  state, stack[128];
>     char      start_buffer[4];
> };
>   

Having an explicit stack is unnecessary I think.  You can use a very 
simple scheme to detect the end of messages by simply counting {}, [], 
and being aware of the lexical rules.

Regards,

Anthony Liguori