Speeding up C implementation

Switch from Sarwate's algorithm to byte-order free Slicing-by-16.
Each table data file is generated by `extconf.rb`.

In addition, the inspection string, which was previously 10 bytes, is extended to 19 bytes.
This is to check the slicing-by-16 loop, which processes in 16-byte units.

Author: dearblue

ext/digest/crc12_3gpp/crc12_3gpp.c

@@ -15,52 +15,42 @@
  */
 
 #include "crc12_3gpp.h"
+#include "extconf.h"
 
-/**
- * Static table used for the table_driven implementation.
- */
-static const crc12_t crc12_table[256] = {
-    0x000, 0x80f, 0x811, 0x01e, 0x82d, 0x022, 0x03c, 0x833, 0x855, 0x05a, 0x044, 0x84b, 0x078, 0x877, 0x869, 0x066,
-    0x8a5, 0x0aa, 0x0b4, 0x8bb, 0x088, 0x887, 0x899, 0x096, 0x0f0, 0x8ff, 0x8e1, 0x0ee, 0x8dd, 0x0d2, 0x0cc, 0x8c3,
-    0x945, 0x14a, 0x154, 0x95b, 0x168, 0x967, 0x979, 0x176, 0x110, 0x91f, 0x901, 0x10e, 0x93d, 0x132, 0x12c, 0x923,
-    0x1e0, 0x9ef, 0x9f1, 0x1fe, 0x9cd, 0x1c2, 0x1dc, 0x9d3, 0x9b5, 0x1ba, 0x1a4, 0x9ab, 0x198, 0x997, 0x989, 0x186,
-    0xa85, 0x28a, 0x294, 0xa9b, 0x2a8, 0xaa7, 0xab9, 0x2b6, 0x2d0, 0xadf, 0xac1, 0x2ce, 0xafd, 0x2f2, 0x2ec, 0xae3,
-    0x220, 0xa2f, 0xa31, 0x23e, 0xa0d, 0x202, 0x21c, 0xa13, 0xa75, 0x27a, 0x264, 0xa6b, 0x258, 0xa57, 0xa49, 0x246,
-    0x3c0, 0xbcf, 0xbd1, 0x3de, 0xbed, 0x3e2, 0x3fc, 0xbf3, 0xb95, 0x39a, 0x384, 0xb8b, 0x3b8, 0xbb7, 0xba9, 0x3a6,
-    0xb65, 0x36a, 0x374, 0xb7b, 0x348, 0xb47, 0xb59, 0x356, 0x330, 0xb3f, 0xb21, 0x32e, 0xb1d, 0x312, 0x30c, 0xb03,
-    0xd05, 0x50a, 0x514, 0xd1b, 0x528, 0xd27, 0xd39, 0x536, 0x550, 0xd5f, 0xd41, 0x54e, 0xd7d, 0x572, 0x56c, 0xd63,
-    0x5a0, 0xdaf, 0xdb1, 0x5be, 0xd8d, 0x582, 0x59c, 0xd93, 0xdf5, 0x5fa, 0x5e4, 0xdeb, 0x5d8, 0xdd7, 0xdc9, 0x5c6,
-    0x440, 0xc4f, 0xc51, 0x45e, 0xc6d, 0x462, 0x47c, 0xc73, 0xc15, 0x41a, 0x404, 0xc0b, 0x438, 0xc37, 0xc29, 0x426,
-    0xce5, 0x4ea, 0x4f4, 0xcfb, 0x4c8, 0xcc7, 0xcd9, 0x4d6, 0x4b0, 0xcbf, 0xca1, 0x4ae, 0xc9d, 0x492, 0x48c, 0xc83,
-    0x780, 0xf8f, 0xf91, 0x79e, 0xfad, 0x7a2, 0x7bc, 0xfb3, 0xfd5, 0x7da, 0x7c4, 0xfcb, 0x7f8, 0xff7, 0xfe9, 0x7e6,
-    0xf25, 0x72a, 0x734, 0xf3b, 0x708, 0xf07, 0xf19, 0x716, 0x770, 0xf7f, 0xf61, 0x76e, 0xf5d, 0x752, 0x74c, 0xf43,
-    0xec5, 0x6ca, 0x6d4, 0xedb, 0x6e8, 0xee7, 0xef9, 0x6f6, 0x690, 0xe9f, 0xe81, 0x68e, 0xebd, 0x6b2, 0x6ac, 0xea3,
-    0x660, 0xe6f, 0xe71, 0x67e, 0xe4d, 0x642, 0x65c, 0xe53, 0xe35, 0x63a, 0x624, 0xe2b, 0x618, 0xe17, 0xe09, 0x606
-};
-
-crc12_t crc_reflect(crc12_t data, size_t data_len)
-{
-	unsigned int i;
-	crc12_t ret = data & 0x01;
-
-	for (i = 1; i < data_len; i++)
-	{
-		data >>= 1;
-		ret = (ret << 1) | (data & 0x01);
-	}
-
-	return ret;
-}
+// This file is generated by generate_table in extconf.rb
+#include "crc12_3gpp_table.h"
 
 crc12_t crc12_3gpp_update(crc12_t crc, const void *data, size_t data_len)
 {
 	const unsigned char *d = (const unsigned char *)data;
 	unsigned int tbl_idx;
 
+	for (; data_len >= SLICE_SIZE; data_len -= SLICE_SIZE)
+	{
+		crc = crc12_3gpp_table[15][d[ 0] ^ ((crc >>  4) & 0xff)] ^
+		      crc12_3gpp_table[14][d[ 1] ^ ((crc <<  4) & 0xff)] ^
+		      crc12_3gpp_table[13][d[ 2]                       ] ^
+		      crc12_3gpp_table[12][d[ 3]                       ] ^
+		      crc12_3gpp_table[11][d[ 4]                       ] ^
+		      crc12_3gpp_table[10][d[ 5]                       ] ^
+		      crc12_3gpp_table[ 9][d[ 6]                       ] ^
+		      crc12_3gpp_table[ 8][d[ 7]                       ] ^
+		      crc12_3gpp_table[ 7][d[ 8]                       ] ^
+		      crc12_3gpp_table[ 6][d[ 9]                       ] ^
+		      crc12_3gpp_table[ 5][d[10]                       ] ^
+		      crc12_3gpp_table[ 4][d[11]                       ] ^
+		      crc12_3gpp_table[ 3][d[12]                       ] ^
+		      crc12_3gpp_table[ 2][d[13]                       ] ^
+		      crc12_3gpp_table[ 1][d[14]                       ] ^
+		      crc12_3gpp_table[ 0][d[15]                       ];
+		crc &= 0xfff;
+		d += SLICE_SIZE;
+	}
+
 	while (data_len--)
 	{
 		tbl_idx = ((crc >> 4) ^ *d) & 0xff;
-		crc = (crc12_table[tbl_idx] ^ (crc << 8)) & 0xfff;
+		crc = (crc12_3gpp_table[0][tbl_idx] ^ (crc << 8)) & 0xfff;
 		d++;
 	}
 

ext/digest/crc12_3gpp/extconf.rb

@@ -1,7 +1,10 @@
 require 'mkmf'
+require_relative '../gentable'
 
 have_header("stdint.h")
 have_header('stddef.h')
 
+generate_table("crc12_3gpp_table.h", "crc12_3gpp_table", 12, 0x080f, false)
+
 create_header
 create_makefile "crc12_3gpp_ext"