用反射输入计算CRC64的最有效方法 [英] Most efficent way to calculate CRC64 with reflected input
本文介绍了用反射输入计算CRC64的最有效方法的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我需要使用此设置到这个精美的网站中计算出CRC-64: http://www.sunshine2k.de/coding/javascript/crc/crc_js.html
I need to calculate a CRC-64 using this setup into this wonderful website: http://www.sunshine2k.de/coding/javascript/crc/crc_js.html
如您所见，我需要反映输入"，这意味着我需要反转任何字节的位顺序(有点烦人).目前，我使用查找表(例如0x55-> 0xAA)实现了此功能，但我想知道是否有CRC的任何属性可以用来提高效率.
As you can see I require "input reflected" and that means that I need to reverse the bit order of any byte (a bit annoying). For the moment, I implemented this with a lookup table (for example 0x55 -> 0xAA), but I was wondering if there is any property of CRC which can be used to be more efficient.
这是我的代码(用C语言编写):
This is my code (in C):
static const unsigned long long CRC64_TABLE[256] = {
0x0000000000000000, 0x42F0E1EBA9EA3693, 0x85E1C3D753D46D26, 0xC711223CFA3E5BB5, 0x493366450E42ECDF, 0x0BC387AEA7A8DA4C, 0xCCD2A5925D9681F9, 0x8E224479F47CB76A,
0x9266CC8A1C85D9BE, 0xD0962D61B56FEF2D, 0x17870F5D4F51B498, 0x5577EEB6E6BB820B, 0xDB55AACF12C73561, 0x99A54B24BB2D03F2, 0x5EB4691841135847, 0x1C4488F3E8F96ED4,
0x663D78FF90E185EF, 0x24CD9914390BB37C, 0xE3DCBB28C335E8C9, 0xA12C5AC36ADFDE5A, 0x2F0E1EBA9EA36930, 0x6DFEFF5137495FA3, 0xAAEFDD6DCD770416, 0xE81F3C86649D3285,
0xF45BB4758C645C51, 0xB6AB559E258E6AC2, 0x71BA77A2DFB03177, 0x334A9649765A07E4, 0xBD68D2308226B08E, 0xFF9833DB2BCC861D, 0x388911E7D1F2DDA8, 0x7A79F00C7818EB3B,
0xCC7AF1FF21C30BDE, 0x8E8A101488293D4D, 0x499B3228721766F8, 0x0B6BD3C3DBFD506B, 0x854997BA2F81E701, 0xC7B97651866BD192, 0x00A8546D7C558A27, 0x4258B586D5BFBCB4,
0x5E1C3D753D46D260, 0x1CECDC9E94ACE4F3, 0xDBFDFEA26E92BF46, 0x990D1F49C77889D5, 0x172F5B3033043EBF, 0x55DFBADB9AEE082C, 0x92CE98E760D05399, 0xD03E790CC93A650A,
0xAA478900B1228E31, 0xE8B768EB18C8B8A2, 0x2FA64AD7E2F6E317, 0x6D56AB3C4B1CD584, 0xE374EF45BF6062EE, 0xA1840EAE168A547D, 0x66952C92ECB40FC8, 0x2465CD79455E395B,
0x3821458AADA7578F, 0x7AD1A461044D611C, 0xBDC0865DFE733AA9, 0xFF3067B657990C3A, 0x711223CFA3E5BB50, 0x33E2C2240A0F8DC3, 0xF4F3E018F031D676, 0xB60301F359DBE0E5,
0xDA050215EA6C212F, 0x98F5E3FE438617BC, 0x5FE4C1C2B9B84C09, 0x1D14202910527A9A, 0x93366450E42ECDF0, 0xD1C685BB4DC4FB63, 0x16D7A787B7FAA0D6, 0x5427466C1E109645,
0x4863CE9FF6E9F891, 0x0A932F745F03CE02, 0xCD820D48A53D95B7, 0x8F72ECA30CD7A324, 0x0150A8DAF8AB144E, 0x43A04931514122DD, 0x84B16B0DAB7F7968, 0xC6418AE602954FFB,
0xBC387AEA7A8DA4C0, 0xFEC89B01D3679253, 0x39D9B93D2959C9E6, 0x7B2958D680B3FF75, 0xF50B1CAF74CF481F, 0xB7FBFD44DD257E8C, 0x70EADF78271B2539, 0x321A3E938EF113AA,
0x2E5EB66066087D7E, 0x6CAE578BCFE24BED, 0xABBF75B735DC1058, 0xE94F945C9C3626CB, 0x676DD025684A91A1, 0x259D31CEC1A0A732, 0xE28C13F23B9EFC87, 0xA07CF2199274CA14,
0x167FF3EACBAF2AF1, 0x548F120162451C62, 0x939E303D987B47D7, 0xD16ED1D631917144, 0x5F4C95AFC5EDC62E, 0x1DBC74446C07F0BD, 0xDAAD56789639AB08, 0x985DB7933FD39D9B,
0x84193F60D72AF34F, 0xC6E9DE8B7EC0C5DC, 0x01F8FCB784FE9E69, 0x43081D5C2D14A8FA, 0xCD2A5925D9681F90, 0x8FDAB8CE70822903, 0x48CB9AF28ABC72B6, 0x0A3B7B1923564425,
0x70428B155B4EAF1E, 0x32B26AFEF2A4998D, 0xF5A348C2089AC238, 0xB753A929A170F4AB, 0x3971ED50550C43C1, 0x7B810CBBFCE67552, 0xBC902E8706D82EE7, 0xFE60CF6CAF321874,
0xE224479F47CB76A0, 0xA0D4A674EE214033, 0x67C58448141F1B86, 0x253565A3BDF52D15, 0xAB1721DA49899A7F, 0xE9E7C031E063ACEC, 0x2EF6E20D1A5DF759, 0x6C0603E6B3B7C1CA,
0xF6FAE5C07D3274CD, 0xB40A042BD4D8425E, 0x731B26172EE619EB, 0x31EBC7FC870C2F78, 0xBFC9838573709812, 0xFD39626EDA9AAE81, 0x3A28405220A4F534, 0x78D8A1B9894EC3A7,
0x649C294A61B7AD73, 0x266CC8A1C85D9BE0, 0xE17DEA9D3263C055, 0xA38D0B769B89F6C6, 0x2DAF4F0F6FF541AC, 0x6F5FAEE4C61F773F, 0xA84E8CD83C212C8A, 0xEABE6D3395CB1A19,
0x90C79D3FEDD3F122, 0xD2377CD44439C7B1, 0x15265EE8BE079C04, 0x57D6BF0317EDAA97, 0xD9F4FB7AE3911DFD, 0x9B041A914A7B2B6E, 0x5C1538ADB04570DB, 0x1EE5D94619AF4648,
0x02A151B5F156289C, 0x4051B05E58BC1E0F, 0x87409262A28245BA, 0xC5B073890B687329, 0x4B9237F0FF14C443, 0x0962D61B56FEF2D0, 0xCE73F427ACC0A965, 0x8C8315CC052A9FF6,
0x3A80143F5CF17F13, 0x7870F5D4F51B4980, 0xBF61D7E80F251235, 0xFD913603A6CF24A6, 0x73B3727A52B393CC, 0x31439391FB59A55F, 0xF652B1AD0167FEEA, 0xB4A25046A88DC879,
0xA8E6D8B54074A6AD, 0xEA16395EE99E903E, 0x2D071B6213A0CB8B, 0x6FF7FA89BA4AFD18, 0xE1D5BEF04E364A72, 0xA3255F1BE7DC7CE1, 0x64347D271DE22754, 0x26C49CCCB40811C7,
0x5CBD6CC0CC10FAFC, 0x1E4D8D2B65FACC6F, 0xD95CAF179FC497DA, 0x9BAC4EFC362EA149, 0x158E0A85C2521623, 0x577EEB6E6BB820B0, 0x906FC95291867B05, 0xD29F28B9386C4D96,
0xCEDBA04AD0952342, 0x8C2B41A1797F15D1, 0x4B3A639D83414E64, 0x09CA82762AAB78F7, 0x87E8C60FDED7CF9D, 0xC51827E4773DF90E, 0x020905D88D03A2BB, 0x40F9E43324E99428,
0x2CFFE7D5975E55E2, 0x6E0F063E3EB46371, 0xA91E2402C48A38C4, 0xEBEEC5E96D600E57, 0x65CC8190991CB93D, 0x273C607B30F68FAE, 0xE02D4247CAC8D41B, 0xA2DDA3AC6322E288,
0xBE992B5F8BDB8C5C, 0xFC69CAB42231BACF, 0x3B78E888D80FE17A, 0x7988096371E5D7E9, 0xF7AA4D1A85996083, 0xB55AACF12C735610, 0x724B8ECDD64D0DA5, 0x30BB6F267FA73B36,
0x4AC29F2A07BFD00D, 0x08327EC1AE55E69E, 0xCF235CFD546BBD2B, 0x8DD3BD16FD818BB8, 0x03F1F96F09FD3CD2, 0x41011884A0170A41, 0x86103AB85A2951F4, 0xC4E0DB53F3C36767,
0xD8A453A01B3A09B3, 0x9A54B24BB2D03F20, 0x5D45907748EE6495, 0x1FB5719CE1045206, 0x919735E51578E56C, 0xD367D40EBC92D3FF, 0x1476F63246AC884A, 0x568617D9EF46BED9,
0xE085162AB69D5E3C, 0xA275F7C11F7768AF, 0x6564D5FDE549331A, 0x279434164CA30589, 0xA9B6706FB8DFB2E3, 0xEB46918411358470, 0x2C57B3B8EB0BDFC5, 0x6EA7525342E1E956,
0x72E3DAA0AA188782, 0x30133B4B03F2B111, 0xF7021977F9CCEAA4, 0xB5F2F89C5026DC37, 0x3BD0BCE5A45A6B5D, 0x79205D0E0DB05DCE, 0xBE317F32F78E067B, 0xFCC19ED95E6430E8,
0x86B86ED5267CDBD3, 0xC4488F3E8F96ED40, 0x0359AD0275A8B6F5, 0x41A94CE9DC428066, 0xCF8B0890283E370C, 0x8D7BE97B81D4019F, 0x4A6ACB477BEA5A2A, 0x089A2AACD2006CB9,
0x14DEA25F3AF9026D, 0x562E43B4931334FE, 0x913F6188692D6F4B, 0xD3CF8063C0C759D8, 0x5DEDC41A34BBEEB2, 0x1F1D25F19D51D821, 0xD80C07CD676F8394, 0x9AFCE626CE85B507
};
static const unsigned char REVERSE_BITS_TABLE[256] = {
// 0 1 2 3 4 5 6 7 8 9 A B C D E F
0x00, 0x80, 0x40, 0xC0, 0x20, 0xA0, 0x60, 0xE0, 0x10, 0x90, 0x50, 0xD0, 0x30, 0xB0, 0x70, 0xF0,
0x08, 0x88, 0x48, 0xC8, 0x28, 0xA8, 0x68, 0xE8, 0x18, 0x98, 0x58, 0xD8, 0x38, 0xB8, 0x78, 0xF8,
0x04, 0x84, 0x44, 0xC4, 0x24, 0xA4, 0x64, 0xE4, 0x14, 0x94, 0x54, 0xD4, 0x34, 0xB4, 0x74, 0xF4,
0x0C, 0x8C, 0x4C, 0xCC, 0x2C, 0xAC, 0x6C, 0xEC, 0x1C, 0x9C, 0x5C, 0xDC, 0x3C, 0xBC, 0x7C, 0xFC,
0x02, 0x82, 0x42, 0xC2, 0x22, 0xA2, 0x62, 0xE2, 0x12, 0x92, 0x52, 0xD2, 0x32, 0xB2, 0x72, 0xF2,
0x0A, 0x8A, 0x4A, 0xCA, 0x2A, 0xAA, 0x6A, 0xEA, 0x1A, 0x9A, 0x5A, 0xDA, 0x3A, 0xBA, 0x7A, 0xFA,
0x06, 0x86, 0x46, 0xC6, 0x26, 0xA6, 0x66, 0xE6, 0x16, 0x96, 0x56, 0xD6, 0x36, 0xB6, 0x76, 0xF6,
0x0E, 0x8E, 0x4E, 0xCE, 0x2E, 0xAE, 0x6E, 0xEE, 0x1E, 0x9E, 0x5E, 0xDE, 0x3E, 0xBE, 0x7E, 0xFE,
0x01, 0x81, 0x41, 0xC1, 0x21, 0xA1, 0x61, 0xE1, 0x11, 0x91, 0x51, 0xD1, 0x31, 0xB1, 0x71, 0xF1,
0x09, 0x89, 0x49, 0xC9, 0x29, 0xA9, 0x69, 0xE9, 0x19, 0x99, 0x59, 0xD9, 0x39, 0xB9, 0x79, 0xF9,
0x05, 0x85, 0x45, 0xC5, 0x25, 0xA5, 0x65, 0xE5, 0x15, 0x95, 0x55, 0xD5, 0x35, 0xB5, 0x75, 0xF5,
0x0D, 0x8D, 0x4D, 0xCD, 0x2D, 0xAD, 0x6D, 0xED, 0x1D, 0x9D, 0x5D, 0xDD, 0x3D, 0xBD, 0x7D, 0xFD,
0x03, 0x83, 0x43, 0xC3, 0x23, 0xA3, 0x63, 0xE3, 0x13, 0x93, 0x53, 0xD3, 0x33, 0xB3, 0x73, 0xF3,
0x0B, 0x8B, 0x4B, 0xCB, 0x2B, 0xAB, 0x6B, 0xEB, 0x1B, 0x9B, 0x5B, 0xDB, 0x3B, 0xBB, 0x7B, 0xFB,
0x07, 0x87, 0x47, 0xC7, 0x27, 0xA7, 0x67, 0xE7, 0x17, 0x97, 0x57, 0xD7, 0x37, 0xB7, 0x77, 0xF7,
0x0F, 0x8F, 0x4F, 0xCF, 0x2F, 0xAF, 0x6F, 0xEF, 0x1F, 0x9F, 0x5F, 0xDF, 0x3F, 0xBF, 0x7F, 0xFF
};
unsigned long long calculateCRC64(unsigned char* data, unsigned long size)
{
unsigned long long myCRC64 = 0;
for(unsigned long i = 0; i < size; i++)
myCRC64 = CRC64_TABLE[((myCRC64 >> 56) ^ REVERSE_BITS_TABLE[data[i]]) & 0xFF] ^ (myCRC64 << 8);
return myCRC64;
}
在此先感谢您的帮助！
更新:实际上，我想知道CRC的某些属性是否允许我使用反射表，相反移位，倒数/倒数多项式...等获得相同的结果.这样可以跳过倒数的步骤.
Update: actually I'm wondering if some properties of CRC allow me to get the same result using reflected table, opposite shifting, reciprocal / reverse polynomial... etc. That would let skip the step of reversing bits.
解决方案:使用反射表，更改移位方向并反转最后一个结果:
Solution: using reflected table, changing shift direction and reversing bits just of the very last result:
static const unsigned long long CRC64_TABLE_REF[256] = {
0x0000000000000000, 0xB32E4CBE03A75F6F, 0xF4843657A840A05B, 0x47AA7AE9ABE7FF34, 0x7BD0C384FF8F5E33, 0xC8FE8F3AFC28015C, 0x8F54F5D357CFFE68, 0x3C7AB96D5468A107,
0xF7A18709FF1EBC66, 0x448FCBB7FCB9E309, 0x0325B15E575E1C3D, 0xB00BFDE054F94352, 0x8C71448D0091E255, 0x3F5F08330336BD3A, 0x78F572DAA8D1420E, 0xCBDB3E64AB761D61,
0x7D9BA13851336649, 0xCEB5ED8652943926, 0x891F976FF973C612, 0x3A31DBD1FAD4997D, 0x064B62BCAEBC387A, 0xB5652E02AD1B6715, 0xF2CF54EB06FC9821, 0x41E11855055BC74E,
0x8A3A2631AE2DDA2F, 0x39146A8FAD8A8540, 0x7EBE1066066D7A74, 0xCD905CD805CA251B, 0xF1EAE5B551A2841C, 0x42C4A90B5205DB73, 0x056ED3E2F9E22447, 0xB6409F5CFA457B28,
0xFB374270A266CC92, 0x48190ECEA1C193FD, 0x0FB374270A266CC9, 0xBC9D3899098133A6, 0x80E781F45DE992A1, 0x33C9CD4A5E4ECDCE, 0x7463B7A3F5A932FA, 0xC74DFB1DF60E6D95,
0x0C96C5795D7870F4, 0xBFB889C75EDF2F9B, 0xF812F32EF538D0AF, 0x4B3CBF90F69F8FC0, 0x774606FDA2F72EC7, 0xC4684A43A15071A8, 0x83C230AA0AB78E9C, 0x30EC7C140910D1F3,
0x86ACE348F355AADB, 0x3582AFF6F0F2F5B4, 0x7228D51F5B150A80, 0xC10699A158B255EF, 0xFD7C20CC0CDAF4E8, 0x4E526C720F7DAB87, 0x09F8169BA49A54B3, 0xBAD65A25A73D0BDC,
0x710D64410C4B16BD, 0xC22328FF0FEC49D2, 0x85895216A40BB6E6, 0x36A71EA8A7ACE989, 0x0ADDA7C5F3C4488E, 0xB9F3EB7BF06317E1, 0xFE5991925B84E8D5, 0x4D77DD2C5823B7BA,
0x64B62BCAEBC387A1, 0xD7986774E864D8CE, 0x90321D9D438327FA, 0x231C512340247895, 0x1F66E84E144CD992, 0xAC48A4F017EB86FD, 0xEBE2DE19BC0C79C9, 0x58CC92A7BFAB26A6,
0x9317ACC314DD3BC7, 0x2039E07D177A64A8, 0x67939A94BC9D9B9C, 0xD4BDD62ABF3AC4F3, 0xE8C76F47EB5265F4, 0x5BE923F9E8F53A9B, 0x1C4359104312C5AF, 0xAF6D15AE40B59AC0,
0x192D8AF2BAF0E1E8, 0xAA03C64CB957BE87, 0xEDA9BCA512B041B3, 0x5E87F01B11171EDC, 0x62FD4976457FBFDB, 0xD1D305C846D8E0B4, 0x96797F21ED3F1F80, 0x2557339FEE9840EF,
0xEE8C0DFB45EE5D8E, 0x5DA24145464902E1, 0x1A083BACEDAEFDD5, 0xA9267712EE09A2BA, 0x955CCE7FBA6103BD, 0x267282C1B9C65CD2, 0x61D8F8281221A3E6, 0xD2F6B4961186FC89,
0x9F8169BA49A54B33, 0x2CAF25044A02145C, 0x6B055FEDE1E5EB68, 0xD82B1353E242B407, 0xE451AA3EB62A1500, 0x577FE680B58D4A6F, 0x10D59C691E6AB55B, 0xA3FBD0D71DCDEA34,
0x6820EEB3B6BBF755, 0xDB0EA20DB51CA83A, 0x9CA4D8E41EFB570E, 0x2F8A945A1D5C0861, 0x13F02D374934A966, 0xA0DE61894A93F609, 0xE7741B60E174093D, 0x545A57DEE2D35652,
0xE21AC88218962D7A, 0x5134843C1B317215, 0x169EFED5B0D68D21, 0xA5B0B26BB371D24E, 0x99CA0B06E7197349, 0x2AE447B8E4BE2C26, 0x6D4E3D514F59D312, 0xDE6071EF4CFE8C7D,
0x15BB4F8BE788911C, 0xA6950335E42FCE73, 0xE13F79DC4FC83147, 0x521135624C6F6E28, 0x6E6B8C0F1807CF2F, 0xDD45C0B11BA09040, 0x9AEFBA58B0476F74, 0x29C1F6E6B3E0301B,
0xC96C5795D7870F42, 0x7A421B2BD420502D, 0x3DE861C27FC7AF19, 0x8EC62D7C7C60F076, 0xB2BC941128085171, 0x0192D8AF2BAF0E1E, 0x4638A2468048F12A, 0xF516EEF883EFAE45,
0x3ECDD09C2899B324, 0x8DE39C222B3EEC4B, 0xCA49E6CB80D9137F, 0x7967AA75837E4C10, 0x451D1318D716ED17, 0xF6335FA6D4B1B278, 0xB199254F7F564D4C, 0x02B769F17CF11223,
0xB4F7F6AD86B4690B, 0x07D9BA1385133664, 0x4073C0FA2EF4C950, 0xF35D8C442D53963F, 0xCF273529793B3738, 0x7C0979977A9C6857, 0x3BA3037ED17B9763, 0x888D4FC0D2DCC80C,
0x435671A479AAD56D, 0xF0783D1A7A0D8A02, 0xB7D247F3D1EA7536, 0x04FC0B4DD24D2A59, 0x3886B22086258B5E, 0x8BA8FE9E8582D431, 0xCC0284772E652B05, 0x7F2CC8C92DC2746A,
0x325B15E575E1C3D0, 0x8175595B76469CBF, 0xC6DF23B2DDA1638B, 0x75F16F0CDE063CE4, 0x498BD6618A6E9DE3, 0xFAA59ADF89C9C28C, 0xBD0FE036222E3DB8, 0x0E21AC88218962D7,
0xC5FA92EC8AFF7FB6, 0x76D4DE52895820D9, 0x317EA4BB22BFDFED, 0x8250E80521188082, 0xBE2A516875702185, 0x0D041DD676D77EEA, 0x4AAE673FDD3081DE, 0xF9802B81DE97DEB1,
0x4FC0B4DD24D2A599, 0xFCEEF8632775FAF6, 0xBB44828A8C9205C2, 0x086ACE348F355AAD, 0x34107759DB5DFBAA, 0x873E3BE7D8FAA4C5, 0xC094410E731D5BF1, 0x73BA0DB070BA049E,
0xB86133D4DBCC19FF, 0x0B4F7F6AD86B4690, 0x4CE50583738CB9A4, 0xFFCB493D702BE6CB, 0xC3B1F050244347CC, 0x709FBCEE27E418A3, 0x3735C6078C03E797, 0x841B8AB98FA4B8F8,
0xADDA7C5F3C4488E3, 0x1EF430E13FE3D78C, 0x595E4A08940428B8, 0xEA7006B697A377D7, 0xD60ABFDBC3CBD6D0, 0x6524F365C06C89BF, 0x228E898C6B8B768B, 0x91A0C532682C29E4,
0x5A7BFB56C35A3485, 0xE955B7E8C0FD6BEA, 0xAEFFCD016B1A94DE, 0x1DD181BF68BDCBB1, 0x21AB38D23CD56AB6, 0x9285746C3F7235D9, 0xD52F0E859495CAED, 0x6601423B97329582,
0xD041DD676D77EEAA, 0x636F91D96ED0B1C5, 0x24C5EB30C5374EF1, 0x97EBA78EC690119E, 0xAB911EE392F8B099, 0x18BF525D915FEFF6, 0x5F1528B43AB810C2, 0xEC3B640A391F4FAD,
0x27E05A6E926952CC, 0x94CE16D091CE0DA3, 0xD3646C393A29F297, 0x604A2087398EADF8, 0x5C3099EA6DE60CFF, 0xEF1ED5546E415390, 0xA8B4AFBDC5A6ACA4, 0x1B9AE303C601F3CB,
0x56ED3E2F9E224471, 0xE5C372919D851B1E, 0xA26908783662E42A, 0x114744C635C5BB45, 0x2D3DFDAB61AD1A42, 0x9E13B115620A452D, 0xD9B9CBFCC9EDBA19, 0x6A978742CA4AE576,
0xA14CB926613CF817, 0x1262F598629BA778, 0x55C88F71C97C584C, 0xE6E6C3CFCADB0723, 0xDA9C7AA29EB3A624, 0x69B2361C9D14F94B, 0x2E184CF536F3067F, 0x9D36004B35545910,
0x2B769F17CF112238, 0x9858D3A9CCB67D57, 0xDFF2A94067518263, 0x6CDCE5FE64F6DD0C, 0x50A65C93309E7C0B, 0xE388102D33392364, 0xA4226AC498DEDC50, 0x170C267A9B79833F,
0xDCD7181E300F9E5E, 0x6FF954A033A8C131, 0x28532E49984F3E05, 0x9B7D62F79BE8616A, 0xA707DB9ACF80C06D, 0x14299724CC279F02, 0x5383EDCD67C06036, 0xE0ADA17364673F59
};
unsigned long long calculateCRC64(unsigned char* data, unsigned long size)
{
unsigned long long myCRC64 = 0;
for(unsigned long i = 0; i < size; i++)
myCRC64 = CRC64_TABLE_REF[(myCRC64 ^ data[i]) & 0xFF] ^ (myCRC64 >> 8);
unsigned long long tmp = myCRC64;
myCRC64 = 0;
for (int i = 0; i < 64; i++) {
myCRC64 = (myCRC64 << 1) | (tmp & 1);
tmp >>= 1;
}
return myCRC64;
}
感谢大家的帮助！
推荐答案
实际上，我想知道CRC的某些属性是否允许我使用反射表，相反移位，倒数/倒数多项式...等获得相同的结果.这样可以跳过反转位的步骤.
actually I'm wondering if some properties of CRC allow me to get the same result using reflected table, opposite shifting, reciprocal / reverse polynomial... etc. That would let skip the step of reversing bits.
有一个这样的属性，最后只需要一个反向即可.CRC的整个逻辑可以进行位反转*，以便位以相反的方式传输，并且在计算过程中无需将其反转:
There is such a property, and you only need one reverse, in the end. The whole logic of the CRC can be bit-reversed*, so that the bits stream the opposite way and don't need to be reversed during the calculation itself:
unsigned long long CRC64(unsigned char* data, unsigned long size)
{
unsigned long long crc = 0;
for(unsigned long i = 0; i < size; i++)
crc = CRC64_TABLE_R[(crc & 0xff) ^ data[i]] ^ (crc >> 8);
return rbit(crc);
}
CRC64_TABLE_R 与 CRC64_TABLE 类似，但是条目和索引都是位反转的.因此它们彼此之间是这样的:(自然，您会对该表进行硬编码)
CRC64_TABLE_R is like CRC64_TABLE, but with the entries and indexes both bit-reversed. So they relate to each other like this: (naturally you would hard-code this table)
for (int i = 0; i < 256; i++) {
CRC64_TABLE_R[REVERSE_BITS_TABLE[i]] = rbit(CRC64_TABLE[i]);
}
rbit 只是一些反转位的功能，我使用了这个非常愚蠢的功能，如果需要，可以使用更好的功能，但只使用一次:
rbit is just some function that reverses bits, I used this really dumb one, use a better one if you want but it's only used once:
unsigned long long rbit(unsigned long long n)
{
unsigned long long x = 0;
for (int i = 0; i < 64; i++) {
x = (x << 1) | (n & 1);
n >>= 1;
}
return x;
}
*:真正的意思是，在计算过程中保持位的整数是相反的，通常是它的最低有效位，而不是最高有效位等.因此，取决于您如何看待它，计算结果甚至没有差异.创建了相同的位，但是我们将它们保存在变量中的方式有所不同.
*: really what this means is that the integer holding the bits during the calculation is viewed in reverse, with what would normally be its least significant bit instead held in its most significant bit etc. So depending on how you look at it, the calculation is not even different. The same bits are created, but we hold them in a variable differently.
这篇关于用反射输入计算CRC64的最有效方法的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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