crc32

问题 I want to calculate a 32-bit CRC lookup table. One way I tried is by using the following code from this website: #include <iostream> #include <stdint.h> void make_crc_table() { unsigned long POLYNOMIAL = 0x04c11db7; unsigned long WIDTH = 8 * sizeof(unsigned long); unsigned long TOPBIT = 1 << (WIDTH - 1); unsigned long crcTable[256]; unsigned long remainder; // Compute the remainder of each possible dividend for (int dividend = 0; dividend < 256; ++dividend) { // Start with the dividend

问题 The bounty expires in 5 days . Answers to this question are eligible for a +50 reputation bounty. bluejayke is looking for a canonical answer : Hi, I and probably many people, have never before heard of CRC32, and all references online seem to be for advanced users only. I need to understand in very simple terms, with a simple example, using any set of bytes as an input, how to calculate the CRC32, from complete beginning to complete end, given a simple string of bytes at section 5.5 of the

问题 Both CRC and hash methods can be used to verify the integrity of the original data. Why do most systems uses hash method nowadays? 回答1: CRC was designed to prevent transmission errors, not malicious action. Therefore, it isn't collision resistant. In particular, the linear properties of CRC codes even allow an attacker to modify a message in such a way as to leave the check value unchanged 回答2: HASH methods (ONE WAY ENCRYPTION) are more complex (and powerful) than simple check codes (CRC).

问题 Are there any 32-bit checksum algorithm with either: Smaller hash collision probability for input data sizes < 1 KB ? Collision hits with more uniform distribution. These relative to CRC32. I'm practically not counting on first property, because of limitation of storage space of 32 bits. But for the second ... seems there could be improvements. Any ideas ? Thanks. (I need concrete implementation, better in C, but C++/ C# or anything to start with is also OK). 回答1: How about MurmurHash? It is

问题 In Ruby: -1104507 ^ 3965973030 => -3966969949 In Javascript: -1104507 ^ 3965973030 => 327997347 Someone asked a similar question here but the answer just pointed to a wrapper for Closure. I need a way to get the same answers from Ruby as I get for JavaScript so I can port this code over. I need a way of being able to get the JavaScript result from any A ^ B in Ruby for any integers A and B . 回答1: Those two are the same result, modulo 2 32 . In Ruby you could & 4294967295 to make the result

问题 I'm attempting to set-up CI for our Xcode cross-compiles. The cross-compiles test both ARMv7 and ARMv8. Things look good except when it comes time to link for ARMv8: clang++ -DNDEBUG -g2 -O3 -fPIC -pipe -Wall -miphoneos-version-min=7 -arch arm64 \ -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS10.2.sdk \ -stdlib=libc++ -c cryptlib.cpp clang++ -DNDEBUG -g2 -O3 -fPIC -pipe -Wall -miphoneos-version-min=7 -arch arm64 \ -isysroot

问题 I have seen many different implementations of the same basic CRC-32 algorithm shown below: int remain; int sbox[SIZESBOX]; int dividend; int bit; for(dividend = 0; dividend < SIZESBOX; dividend++) { remain = dividend << 24; for(bit = 0; bit < 8; bit++) { if(remain & TOPBIT) { remain = (remain << 1) ^ POLYNOMIAL; } else { remain = (remain << 1); } } sbox[dividend] = remain; } Some of them XOR the dividend before going into the sbox. Others XOR before going into the bit loop, and others use

问题 I'm trying to calculate/generate the CRC32 hash of some random strings using Python but they do not match the values I generate from online sources. Here is what I'm doing on my PC, >>> import binascii >>> binascii.crc32('hello-world') -1311505829 Another approach, >>> import zlib >>> zlib.crc32('hello-world') -1311505829 The fact that the above results are identical tells me that I'm calling the function correctly. But, if I go to the following online sources, http://www.lammertbies.nl/comm

问题 I'm trying to calculate/generate the CRC32 hash of some random strings using Python but they do not match the values I generate from online sources. Here is what I'm doing on my PC, >>> import binascii >>> binascii.crc32('hello-world') -1311505829 Another approach, >>> import zlib >>> zlib.crc32('hello-world') -1311505829 The fact that the above results are identical tells me that I'm calling the function correctly. But, if I go to the following online sources, http://www.lammertbies.nl/comm

问题 I do check sum of classes.dex in native code as indicated here: Check .apk-signature in C/native Code Calculate checksum of classes.dex compare with hardcoded value - xxx if it's true, pass and go on if it's not true, exit the app What I do is log the checksum value for the first build, then change the if (checksum == xxx) in native code to be the same as the logged value. However, with using Dexguard, the checksum is different for every different build, means that if I change xxx, and