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f262fce616
Add another difficult needle to strstr that clearly shows the quadratic complexity of bruteforce algorithms. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
454 lines
14 KiB
C
454 lines
14 KiB
C
/* Measure strstr functions.
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Copyright (C) 2013-2024 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#define MIN_PAGE_SIZE 131072
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#define TEST_MAIN
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#define TEST_NAME "strstr"
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#include "bench-string.h"
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#include "json-lib.h"
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static const char input[] =
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"This manual is written with the assumption that you are at least "
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"somewhat familiar with the C programming language and basic programming "
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"concepts. Specifically, familiarity with ISO standard C (*note ISO "
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"C::), rather than “traditional” pre-ISO C dialects, is assumed.\n"
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" The GNU C Library includes several “header files”, each of which "
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"provides definitions and declarations for a group of related facilities; "
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"this information is used by the C compiler when processing your program. "
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"For example, the header file ‘stdio.h’ declares facilities for "
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"performing input and output, and the header file ‘string.h’ declares "
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"string processing utilities. The organization of this manual generally "
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"follows the same division as the header files.\n"
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" If you are reading this manual for the first time, you should read "
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"all of the introductory material and skim the remaining chapters. There "
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"are a _lot_ of functions in the GNU C Library and it’s not realistic to "
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"expect that you will be able to remember exactly _how_ to use each and "
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"every one of them. It’s more important to become generally familiar "
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"with the kinds of facilities that the library provides, so that when you "
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"are writing your programs you can recognize _when_ to make use of "
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"library functions, and _where_ in this manual you can find more specific "
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"information about them.\n";
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/* Simple yet efficient strstr - for needles < 32 bytes it is 2-4 times
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faster than the optimized twoway_strstr. */
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static char *
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basic_strstr (const char *s1, const char *s2)
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{
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size_t i;
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int c = s2[0];
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if (c == 0)
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return (char*)s1;
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for ( ; s1[0] != '\0'; s1++)
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{
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if (s1[0] != c)
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continue;
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for (i = 1; s2[i] != 0; i++)
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if (s1[i] != s2[i])
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break;
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if (s2[i] == '\0')
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return (char*)s1;
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}
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return NULL;
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}
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#define RETURN_TYPE char *
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#define AVAILABLE(h, h_l, j, n_l) \
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(((j) + (n_l) <= (h_l)) \
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|| ((h_l) += __strnlen ((void*)((h) + (h_l)), (n_l) + 512), \
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(j) + (n_l) <= (h_l)))
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#define CHECK_EOL (1)
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#define RET0_IF_0(a) if (!a) goto ret0
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#define FASTSEARCH(S,C,N) (void*) strchr ((void*)(S), (C))
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#define LONG_NEEDLE_THRESHOLD 32U
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#define __strnlen strnlen
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#include "string/str-two-way.h"
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/* Optimized Two-way implementation from GLIBC 2.29. */
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static char *
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twoway_strstr (const char *haystack, const char *needle)
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{
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size_t needle_len; /* Length of NEEDLE. */
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size_t haystack_len; /* Known minimum length of HAYSTACK. */
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/* Handle empty NEEDLE special case. */
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if (needle[0] == '\0')
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return (char *) haystack;
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/* Skip until we find the first matching char from NEEDLE. */
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haystack = strchr (haystack, needle[0]);
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if (haystack == NULL || needle[1] == '\0')
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return (char *) haystack;
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/* Ensure HAYSTACK length is at least as long as NEEDLE length.
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Since a match may occur early on in a huge HAYSTACK, use strnlen
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and read ahead a few cachelines for improved performance. */
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needle_len = strlen (needle);
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haystack_len = __strnlen (haystack, needle_len + 256);
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if (haystack_len < needle_len)
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return NULL;
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/* Check whether we have a match. This improves performance since we avoid
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the initialization overhead of the two-way algorithm. */
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if (memcmp (haystack, needle, needle_len) == 0)
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return (char *) haystack;
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/* Perform the search. Abstract memory is considered to be an array
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of 'unsigned char' values, not an array of 'char' values. See
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ISO C 99 section 6.2.6.1. */
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if (needle_len < LONG_NEEDLE_THRESHOLD)
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return two_way_short_needle ((const unsigned char *) haystack,
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haystack_len,
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(const unsigned char *) needle, needle_len);
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return two_way_long_needle ((const unsigned char *) haystack, haystack_len,
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(const unsigned char *) needle, needle_len);
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}
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typedef char *(*proto_t) (const char *, const char *);
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IMPL (strstr, 1)
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IMPL (twoway_strstr, 0)
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IMPL (basic_strstr, 0)
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static void
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do_one_test (json_ctx_t *json_ctx, impl_t *impl, const char *s1,
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const char *s2, char *exp_result)
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{
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size_t i, iters = INNER_LOOP_ITERS_SMALL / 8;
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timing_t start, stop, cur;
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char *res;
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TIMING_NOW (start);
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for (i = 0; i < iters; ++i)
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res = CALL (impl, s1, s2);
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TIMING_NOW (stop);
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TIMING_DIFF (cur, start, stop);
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json_element_double (json_ctx, (double) cur / (double) iters);
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if (res != exp_result)
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{
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error (0, 0, "Wrong result in function %s %s %s", impl->name,
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(res == NULL) ? "(null)" : res,
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(exp_result == NULL) ? "(null)" : exp_result);
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ret = 1;
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}
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}
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static void
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do_test (json_ctx_t *json_ctx, size_t align1, size_t align2, size_t len1,
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size_t len2, int fail)
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{
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char *s1 = (char *) (buf1 + align1);
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char *s2 = (char *) (buf2 + align2);
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size_t size = sizeof (input) - 1;
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size_t pos = (len1 + len2) % size;
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char *ss2 = s2;
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for (size_t l = len2; l > 0; l = l > size ? l - size : 0)
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{
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size_t t = l > size ? size : l;
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if (pos + t <= size)
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ss2 = mempcpy (ss2, input + pos, t);
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else
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{
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ss2 = mempcpy (ss2, input + pos, size - pos);
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ss2 = mempcpy (ss2, input, t - (size - pos));
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}
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}
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s2[len2] = '\0';
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char *ss1 = s1;
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for (size_t l = len1; l > 0; l = l > size ? l - size : 0)
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{
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size_t t = l > size ? size : l;
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memcpy (ss1, input, t);
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ss1 += t;
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}
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if (!fail)
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memcpy (s1 + len1 - len2, s2, len2);
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s1[len1] = '\0';
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/* Remove any accidental matches except for the last if !fail. */
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for (ss1 = basic_strstr (s1, s2); ss1; ss1 = basic_strstr (ss1 + 1, s2))
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if (fail || ss1 != s1 + len1 - len2)
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++ss1[len2 / 2];
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json_element_object_begin (json_ctx);
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json_attr_uint (json_ctx, "len_haystack", len1);
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json_attr_uint (json_ctx, "len_needle", len2);
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json_attr_uint (json_ctx, "align_haystack", align1);
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json_attr_uint (json_ctx, "align_needle", align2);
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json_attr_uint (json_ctx, "fail", fail);
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json_array_begin (json_ctx, "timings");
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FOR_EACH_IMPL (impl, 0)
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do_one_test (json_ctx, impl, s1, s2, fail ? NULL : s1 + len1 - len2);
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json_array_end (json_ctx);
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json_element_object_end (json_ctx);
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}
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/* Test needles which exhibit worst-case performance. This shows that
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basic_strstr is quadratic and thus unsuitable for large needles.
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On the other hand Two-way and skip table implementations are linear with
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increasing needle sizes. The slowest cases of the two implementations are
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within a factor of 2 on several different microarchitectures. */
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static void
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test_hard_needle (json_ctx_t *json_ctx, size_t ne_len, size_t hs_len)
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{
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char *ne = (char *) buf1;
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char *hs = (char *) buf2;
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/* Hard needle for strstr algorithm using skip table. This results in many
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memcmp calls comparing most of the needle. */
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{
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memset (ne, 'a', ne_len);
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ne[ne_len] = '\0';
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ne[ne_len - 14] = 'b';
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memset (hs, 'a', hs_len);
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for (size_t i = ne_len; i <= hs_len; i += ne_len)
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{
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hs[i - 5] = 'b';
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hs[i - 62] = 'b';
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}
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json_element_object_begin (json_ctx);
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json_attr_uint (json_ctx, "len_haystack", hs_len);
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json_attr_uint (json_ctx, "len_needle", ne_len);
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json_attr_uint (json_ctx, "align_haystack", 0);
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json_attr_uint (json_ctx, "align_needle", 0);
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json_attr_uint (json_ctx, "fail", 1);
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json_attr_string (json_ctx, "desc", "Difficult skiptable(0)");
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json_array_begin (json_ctx, "timings");
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FOR_EACH_IMPL (impl, 0)
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do_one_test (json_ctx, impl, hs, ne, NULL);
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json_array_end (json_ctx);
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json_element_object_end (json_ctx);
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}
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/* 2nd hard needle for strstr algorithm using skip table. This results in
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many memcmp calls comparing most of the needle. */
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{
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memset (ne, 'a', ne_len);
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ne[ne_len] = '\0';
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ne[ne_len - 6] = 'b';
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memset (hs, 'a', hs_len);
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for (size_t i = ne_len; i <= hs_len; i += ne_len)
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{
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hs[i - 5] = 'b';
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hs[i - 6] = 'b';
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}
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json_element_object_begin (json_ctx);
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json_attr_uint (json_ctx, "len_haystack", hs_len);
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json_attr_uint (json_ctx, "len_needle", ne_len);
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json_attr_uint (json_ctx, "align_haystack", 0);
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json_attr_uint (json_ctx, "align_needle", 0);
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json_attr_uint (json_ctx, "fail", 1);
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json_attr_string (json_ctx, "desc", "Difficult skiptable(1)");
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json_array_begin (json_ctx, "timings");
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FOR_EACH_IMPL (impl, 0)
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do_one_test (json_ctx, impl, hs, ne, NULL);
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json_array_end (json_ctx);
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json_element_object_end (json_ctx);
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}
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/* Hard needle for Two-way algorithm - the random input causes a large number
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of branch mispredictions which significantly reduces performance on modern
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micro architectures. */
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{
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for (int i = 0; i < hs_len; i++)
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hs[i] = (rand () & 255) > 155 ? 'a' : 'b';
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hs[hs_len] = 0;
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memset (ne, 'a', ne_len);
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ne[ne_len - 2] = 'b';
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ne[0] = 'b';
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ne[ne_len] = 0;
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json_element_object_begin (json_ctx);
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json_attr_uint (json_ctx, "len_haystack", hs_len);
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json_attr_uint (json_ctx, "len_needle", ne_len);
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json_attr_uint (json_ctx, "align_haystack", 0);
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json_attr_uint (json_ctx, "align_needle", 0);
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json_attr_uint (json_ctx, "fail", 1);
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json_attr_string (json_ctx, "desc", "Difficult 2-way");
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json_array_begin (json_ctx, "timings");
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FOR_EACH_IMPL (impl, 0)
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do_one_test (json_ctx, impl, hs, ne, NULL);
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json_array_end (json_ctx);
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json_element_object_end (json_ctx);
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}
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/* Hard needle for standard algorithm testing first few characters of
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* needle. */
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{
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for (int i = 0; i < hs_len; i++)
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hs[i] = (rand () & 255) >= 128 ? 'a' : 'b';
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hs[hs_len] = 0;
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for (int i = 0; i < ne_len; i++)
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{
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if (i % 3 == 0)
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ne[i] = 'a';
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else if (i % 3 == 1)
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ne[i] = 'b';
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else
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ne[i] = 'c';
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}
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ne[ne_len] = 0;
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json_element_object_begin (json_ctx);
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json_attr_uint (json_ctx, "len_haystack", hs_len);
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json_attr_uint (json_ctx, "len_needle", ne_len);
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json_attr_uint (json_ctx, "align_haystack", 0);
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json_attr_uint (json_ctx, "align_needle", 0);
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json_attr_uint (json_ctx, "fail", 1);
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json_attr_string (json_ctx, "desc", "Difficult testing first 2");
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json_array_begin (json_ctx, "timings");
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FOR_EACH_IMPL (impl, 0)
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do_one_test (json_ctx, impl, hs, ne, NULL);
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json_array_end (json_ctx);
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json_element_object_end (json_ctx);
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}
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/* Hard needle for bruteforce algorithms that match first few chars. */
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{
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memset (hs, 'a', hs_len);
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for (int i = ne_len-1; i < hs_len; i += ne_len)
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hs[i] = 'b';
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hs[hs_len] = 0;
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memset (ne, 'a', ne_len);
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ne[ne_len] = 0;
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json_element_object_begin (json_ctx);
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json_attr_uint (json_ctx, "len_haystack", hs_len);
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json_attr_uint (json_ctx, "len_needle", ne_len);
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json_attr_uint (json_ctx, "align_haystack", 0);
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json_attr_uint (json_ctx, "align_needle", 0);
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json_attr_uint (json_ctx, "fail", 1);
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json_attr_string (json_ctx, "desc", "Difficult bruteforce needle");
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json_array_begin (json_ctx, "timings");
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FOR_EACH_IMPL (impl, 0)
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do_one_test (json_ctx, impl, hs, ne, NULL);
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json_array_end (json_ctx);
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json_element_object_end (json_ctx);
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}
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}
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static int
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test_main (void)
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{
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json_ctx_t json_ctx;
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test_init ();
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json_init (&json_ctx, 0, stdout);
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json_document_begin (&json_ctx);
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json_attr_string (&json_ctx, "timing_type", TIMING_TYPE);
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json_attr_object_begin (&json_ctx, "functions");
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json_attr_object_begin (&json_ctx, TEST_NAME);
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json_attr_string (&json_ctx, "bench-variant", "");
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json_array_begin (&json_ctx, "ifuncs");
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FOR_EACH_IMPL (impl, 0)
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json_element_string (&json_ctx, impl->name);
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json_array_end (&json_ctx);
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json_array_begin (&json_ctx, "results");
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for (size_t hlen = 8; hlen <= 256;)
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for (size_t klen = 1; klen <= 16; klen++)
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{
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do_test (&json_ctx, 1, 3, hlen, klen, 0);
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do_test (&json_ctx, 0, 9, hlen, klen, 1);
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do_test (&json_ctx, 1, 3, hlen + 1, klen, 0);
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do_test (&json_ctx, 0, 9, hlen + 1, klen, 1);
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do_test (&json_ctx, getpagesize () - 15, 9, hlen, klen, 1);
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if (hlen < 64)
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{
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hlen += 8;
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}
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else
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{
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hlen += 32;
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}
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}
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for (size_t hlen = 256; hlen <= 65536; hlen *= 2)
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for (size_t klen = 4; klen <= 256; klen *= 2)
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{
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do_test (&json_ctx, 1, 11, hlen, klen, 0);
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do_test (&json_ctx, 14, 5, hlen, klen, 1);
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do_test (&json_ctx, 1, 11, hlen + 1, klen + 1, 0);
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do_test (&json_ctx, 14, 5, hlen + 1, klen + 1, 1);
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do_test (&json_ctx, 1, 11, hlen + 1, klen, 0);
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do_test (&json_ctx, 14, 5, hlen + 1, klen, 1);
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do_test (&json_ctx, getpagesize () - 15, 5, hlen + 1, klen, 1);
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}
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test_hard_needle (&json_ctx, 64, 65536);
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test_hard_needle (&json_ctx, 256, 65536);
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test_hard_needle (&json_ctx, 1024, 65536);
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json_array_end (&json_ctx);
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json_attr_object_end (&json_ctx);
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json_attr_object_end (&json_ctx);
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json_document_end (&json_ctx);
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return ret;
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}
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#include <support/test-driver.c>
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