* [Confirmed for long needles] Fastest String Search Algorithm.
@ 2021-06-15 20:22 Amit Choudhary
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From: Amit Choudhary @ 2021-06-15 20:22 UTC (permalink / raw)
To: GNU C Library
[-- Attachment #1: Type: text/plain, Size: 2543 bytes --]
Hi,
In case someone is interested, else please ignore (just sending on
public domain for other people if they do web search) [Tested on
latest glibc - glibc-2.33].
I have done final testing with long needles. I modified bench-strstr.c
and included my algorithm in it.
Attached are the diff, analysis.xlsx, and original bench-strstr.out.
Below is my code:
==============================================================================================
// Choudhary algorithm
static char *
chal(char *text, char *pattern)
{
#define false 0
#define true 1
#define ALPHABET_SIZE 256
long i = 0;
long index = 0;
long end_index = 0;
int not_found = false;
long text_len = strlen(text);
long pattern_len = strlen(pattern);
long pi_44 = pattern_len - 1;
long pi_34 = (3 * pattern_len) / 4;
long pi_24 = pattern_len / 2;
long pi_14 = pattern_len / 4;
long fps = 0;
long skip_table[ALPHABET_SIZE] = {0};
// preprocess pattern and fill skip_table
for (i = 0; i < pattern_len; i++) {
skip_table[(int)(pattern[i])] = pattern_len - 1 - i;
}
// now search
for (i = 0; i < text_len; i++) {
if ((text_len - i) < pattern_len) {
//printf("\tfps = %ld\n", fps);
return NULL;
//return -1;
}
if (pattern[pi_44] != text[i + pi_44]) {
if (skip_table[(int)(text[i + pi_44])] > 0) {
i = i + skip_table[(int)(text[i + pi_44])] - 1;
}
continue;
}
if (pattern[0] != text[i]) {
continue;
}
if (pattern[pi_24] != text[i + pi_24]) {
continue;
}
if (pattern[pi_34] != text[i + pi_34]) {
continue;
}
if (pattern[pi_14] != text[i + pi_14]) {
continue;
}
fps = fps + 1;
end_index = i + pi_44;
not_found = false;
for (index = i; index <= end_index; index++) {
if (text[index] != pattern[index - i]) {
not_found = true;
break;
}
} // end of inner for loop
if (not_found == false) { // match is found
//printf("\tfps = %ld\n", fps);
return (text + i);
//return i;
}
} // end of outer for loop
//printf("\tfps = %ld\n", fps);
return NULL;
//return -1;
} // end of chal
==============================================================================================
Amit
[-- Attachment #2: analysis.xlsx --]
[-- Type: application/vnd.openxmlformats-officedocument.spreadsheetml.sheet, Size: 8878 bytes --]
[-- Attachment #3: glibc-2.33.diff --]
[-- Type: text/x-patch, Size: 3991 bytes --]
diff -ru glibc-2.33.orig/benchtests/bench-strstr.c glibc-2.33/benchtests/bench-strstr.c
--- glibc-2.33.orig/benchtests/bench-strstr.c 2021-02-01 22:45:33.000000000 +0530
+++ glibc-2.33/benchtests/bench-strstr.c 2021-06-16 01:22:34.320912352 +0530
@@ -45,6 +45,8 @@
"library functions, and _where_ in this manual you can find more specific "
"information about them.\n";
+static char *chal(char *text, char *pattern);
+
/* Simple yet efficient strstr - for needles < 32 bytes it is 2-4 times
faster than the optimized twoway_strstr. */
static char *
@@ -125,6 +127,7 @@
typedef char *(*proto_t) (const char *, const char *);
IMPL (strstr, 1)
+IMPL (chal, 0)
IMPL (twoway_strstr, 0)
IMPL (basic_strstr, 0)
@@ -210,6 +213,7 @@
increasing needle sizes. The slowest cases of the two implementations are
within a factor of 2 on several different microarchitectures. */
+#if 0
static void
test_hard_needle (size_t ne_len, size_t hs_len)
{
@@ -278,6 +282,94 @@
putchar ('\n');
}
}
+#endif
+
+// Choudhary algorithm
+static char *
+chal(char *text, char *pattern)
+{
+
+#define false 0
+#define true 1
+#define ALPHABET_SIZE 256
+
+ long i = 0;
+ long index = 0;
+ long end_index = 0;
+ int not_found = false;
+
+ long text_len = strlen(text);
+ long pattern_len = strlen(pattern);
+
+ long pi_44 = pattern_len - 1;
+ long pi_34 = (3 * pattern_len) / 4;
+ long pi_24 = pattern_len / 2;
+ long pi_14 = pattern_len / 4;
+
+ long fps = 0;
+ long skip_table[ALPHABET_SIZE] = {0};
+
+ // preprocess pattern and fill skip_table
+ for (i = 0; i < pattern_len; i++) {
+ skip_table[(int)(pattern[i])] = pattern_len - 1 - i;
+ }
+
+ // now search
+ for (i = 0; i < text_len; i++) {
+
+ if ((text_len - i) < pattern_len) {
+ //printf("\tfps = %ld\n", fps);
+ return NULL;
+ //return -1;
+ }
+
+ if (pattern[pi_44] != text[i + pi_44]) {
+ if (skip_table[(int)(text[i + pi_44])] > 0) {
+ i = i + skip_table[(int)(text[i + pi_44])] - 1;
+ }
+ continue;
+ }
+
+ if (pattern[0] != text[i]) {
+ continue;
+ }
+
+ if (pattern[pi_24] != text[i + pi_24]) {
+ continue;
+ }
+
+ if (pattern[pi_34] != text[i + pi_34]) {
+ continue;
+ }
+
+ if (pattern[pi_14] != text[i + pi_14]) {
+ continue;
+ }
+
+ fps = fps + 1;
+ end_index = i + pi_44;
+ not_found = false;
+
+ for (index = i; index <= end_index; index++) {
+ if (text[index] != pattern[index - i]) {
+ not_found = true;
+ break;
+ }
+ } // end of inner for loop
+
+ if (not_found == false) { // match is found
+ //printf("\tfps = %ld\n", fps);
+ return (text + i);
+ //return i;
+ }
+
+ } // end of outer for loop
+
+ //printf("\tfps = %ld\n", fps);
+ return NULL;
+ //return -1;
+
+} // end of chal
static int
test_main (void)
@@ -292,20 +384,21 @@
for (size_t hlen = 64; hlen <= 256; hlen += 32)
for (size_t klen = 1; klen <= 16; klen++)
{
- do_test (1, 3, hlen, klen, 0);
- do_test (0, 9, hlen, klen, 1);
+ //do_test (1, 3, hlen, klen, 0);
+ //do_test (0, 9, hlen, klen, 1);
}
- for (size_t hlen = 256; hlen <= 65536; hlen *= 2)
- for (size_t klen = 16; klen <= 256; klen *= 2)
+ for (size_t hlen = 1024; hlen <= 65536; hlen *= 2)
+ //for (size_t klen = 16; klen <= 256; klen *= 2)
+ for (size_t klen = 1024; klen <= hlen; klen *= 2)
{
do_test (1, 11, hlen, klen, 0);
do_test (14, 5, hlen, klen, 1);
}
- test_hard_needle (64, 65536);
- test_hard_needle (256, 65536);
- test_hard_needle (1024, 65536);
+ //test_hard_needle (64, 65536);
+ //test_hard_needle (256, 65536);
+ //test_hard_needle (1024, 65536);
return ret;
}
[-- Attachment #4: bench-strstr.out --]
[-- Type: application/octet-stream, Size: 4607 bytes --]
basic_strstr twoway_strstr chal __strstr_sse2_unaligned __strstr_sse2
Length 1024/1024, alignment 1/11, found: 2089.06 428.125 12255.5 4561.72 429.688
Length 1024/1024, alignment 14/ 5, fail : 4536.72 299.219 9113.28 974.219 224.219
Length 2048/1024, alignment 1/11, found: 9598.44 20886.7 12909.4 3925 20866.4
Length 2048/1024, alignment 14/ 5, fail : 12341.4 18972.7 8628.91 3103.91 19281.2
Length 2048/2048, alignment 1/11, found: 4476.56 625 21861.7 8421.88 651.562
Length 2048/2048, alignment 14/ 5, fail : 14996.9 340.625 18109.4 9892.97 389.844
Length 4096/1024, alignment 1/11, found: 14972.7 22117.2 14968.8 6058.59 22322.7
Length 4096/1024, alignment 14/ 5, fail : 17291.4 20445.3 11021.9 4682.81 20541.4
Length 4096/2048, alignment 1/11, found: 16896.1 39532.8 24222.7 43337.5 40996.9
Length 4096/2048, alignment 14/ 5, fail : 30721.1 39861.7 18486.7 8394.53 38468
Length 4096/4096, alignment 1/11, found: 9270.31 1419.53 50182 16295.3 1282.81
Length 4096/4096, alignment 14/ 5, fail : 37185.9 603.125 11363.3 10475 975
Length 8192/1024, alignment 1/11, found: 79155.5 44248.4 15274.2 17704.7 26135.2
Length 8192/1024, alignment 14/ 5, fail : 71643 21028.9 10257 16943 34669.5
Length 8192/2048, alignment 1/11, found: 59628.9 35382.8 12239.1 15216.4 35798.4
Length 8192/2048, alignment 14/ 5, fail : 37575 24750 7460.16 15131.2 21144.5
Length 8192/4096, alignment 1/11, found: 42871.9 76123.4 33758.6 37295.3 31769.5
Length 8192/4096, alignment 14/ 5, fail : 39203.9 40171.9 10601.6 36032 32105.5
Length 8192/8192, alignment 1/11, found: 13257.8 2188.28 41884.4 22994.5 1785.94
Length 8192/8192, alignment 14/ 5, fail : 43484.4 800.781 22860.9 10253.1 772.656
Length 16384/1024, alignment 1/11, found: 54652.3 23450.8 16033.6 16032 20920.3
Length 16384/1024, alignment 14/ 5, fail : 55950 20818 14721.9 15960.2 19725.8
Length 16384/2048, alignment 1/11, found: 33974.2 30698.4 14841.4 16936.7 29123.4
Length 16384/2048, alignment 14/ 5, fail : 43609.4 54007.8 15832.8 28162.5 31682
Length 16384/4096, alignment 1/11, found: 45509.4 51984.4 25340.6 64178.1 40407
Length 16384/4096, alignment 14/ 5, fail : 44695.3 47563.3 18793 40025.8 38476.6
Length 16384/8192, alignment 1/11, found: 76010.9 88800.8 28921.1 82950 67578.1
Length 16384/8192, alignment 14/ 5, fail : 111872 108791 29732 79808.6 80371.1
Length 16384/16384, alignment 1/11, found: 25663.3 2778.91 54814.1 32831.2 2764.06
Length 16384/16384, alignment 14/ 5, fail : 171498 1650 38649.2 20471.1 1378.12
Length 32768/1024, alignment 1/11, found: 114112 37924.2 24429.7 32809.4 36200
Length 32768/1024, alignment 14/ 5, fail : 115409 35757.8 23677.3 22817.2 35640.6
Length 32768/2048, alignment 1/11, found: 111464 29918 22440.6 57910.2 29357.8
Length 32768/2048, alignment 14/ 5, fail : 122780 38343.8 31703.9 70637.5 28878.9
Length 32768/4096, alignment 1/11, found: 161623 86311.7 40021.1 61573.4 83786.7
Length 32768/4096, alignment 14/ 5, fail : 168648 94081.2 62041.4 57056.2 54064.8
Length 32768/8192, alignment 1/11, found: 190786 153845 51453.9 120277 93224.2
Length 32768/8192, alignment 14/ 5, fail : 224271 137055 50689.1 109388 85260.9
Length 32768/16384, alignment 1/11, found: 291351 238527 59493 162361 138698
Length 32768/16384, alignment 14/ 5, fail : 363070 195028 85438.3 192824 168337
Length 32768/32768, alignment 1/11, found: 33070.3 5542.97 349531 80743.8 6096.88
Length 32768/32768, alignment 14/ 5, fail : 991841 4489.84 288573 73746.9 5169.53
Length 65536/1024, alignment 1/11, found: 260891 61587.5 37722.7 51047.7 90785.9
Length 65536/1024, alignment 14/ 5, fail : 355538 54465.6 27995.3 61132 47860.2
Length 65536/2048, alignment 1/11, found: 252798 80010.9 43000.8 81523.4 91832
Length 65536/2048, alignment 14/ 5, fail : 373905 91524.2 41894.5 75481.2 73662.5
Length 65536/4096, alignment 1/11, found: 338044 104859 70168.8 97125 118416
Length 65536/4096, alignment 14/ 5, fail : 366308 97412.5 65432.8 93324.2 97521.1
Length 65536/8192, alignment 1/11, found: 368997 162164 144940 131199 124479
Length 65536/8192, alignment 14/ 5, fail : 337055 135984 114395 133409 196736
Length 65536/16384, alignment 1/11, found: 525169 509878 372732 450800 444905
Length 65536/16384, alignment 14/ 5, fail : 623478 484677 391644 460172 427140
Length 65536/32768, alignment 1/11, found: 981066 797843 348248 598640 582176
Length 65536/32768, alignment 14/ 5, fail : 897535 570133 469474 537280 496208
Length 65536/65536, alignment 1/11, found: 67847.7 10714.8 646270 151578 10800
Length 65536/65536, alignment 14/ 5, fail : 2.91258e+06 5287.5 552998 152034 9558.59
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