crc32

问题 If I want to calculate the CRC32 value for a large number of consecutive zero bytes, is there a constant time formula I can use given the length of the run of zeros? For example, if I know I have 1000 bytes all filled with zeros, is there a way to avoid a loop with 1000 iterations (just an example, actual number of zeros is unbounded for the sake of this question)? 回答1: You can compute the result of applying n zeros not in O(1) time, but in O(log n ) time. This is done in zlib's crc32_combine

问题 I'm trying to calculate/validate the CRC32 checksums for compressed bzip2 archives. .magic:16 = 'BZ' signature/magic number .version:8 = 'h' for Bzip2 ('H'uffman coding) .hundred_k_blocksize:8 = '1'..'9' block-size 100 kB-900 kB .compressed_magic:48 = 0x314159265359 (BCD (pi)) .crc:32 = checksum for this block ... ... .eos_magic:48 = 0x177245385090 (BCD sqrt(pi)) .crc:32 = checksum for whole stream .padding:0..7 = align to whole byte http://en.wikipedia.org/wiki/Bzip2 So I know where the CRC

问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 5 years ago . I am trying to implement a CRC32 algorithm in C that does not use a look up table (I need to use it in a boot loader that doesn't have enough memory available to have one). Is there an available solution to this that has a public license? 回答1: A quick search harvested this webpage. I wasn't able to find the

问题 Intel has a specific CRC32 instruction available in the SSE4.2 instruction set. How can I take advantage of this instruction to speed up CRC32 calculations? 回答1: First of all the Intel's CRC32 instruction serves to calculate CRC-32C (that is uses a different polynomial that regular CRC32. Look at the Wikipedia CRC32 entry) To use Intel's hardware acceleration for CRC32C using gcc you can: Inline assembly language in C code via the asm statement Use intrinsics _mm_crc32_u8 , _mm_crc32_u16 ,

问题 I generate a traffic between two PCs running Linux (by sending Ethernet frames), the goal of this is to capture some errors frames. The problem is when the Phy layer detect an error on a frame (if the CRC or FCS is not valid) the frame is dropped and I can't receive it in my program. Are the any way to receive the wrong frame (disable the drops in the Phy layer and receiving a indicator that indicate that this frame is wrong for example) and how can i consult the statistic of the NIC card

问题 Given that SSE 4.2 (Intel Core i7 & i5 parts) includes a CRC32 instruction, it seems reasonable to investigate whether one could build a faster general-purpose hash function. According to this only 16 bits of a CRC32 are evenly distributed. So what other transformation would one apply to overcome that? Update How about this? Only 16 bits are suitable for a hash value. Fine. If your table is 65535 or less then great. If not, run the CRC value through the Nehalem POPCNT (population count)

问题 I did explore Crcmod python library but couldnt use it as my gen poly- 0x1EDC6F41 is not considered a 32 bit poly :( Is there a way to tweak it or any other python lib that I can use to do this? Name : "CRC-32C" Width : 32 Poly : 1EDC6F41h Init : FFFFFFFFh RefIn : True RefOut : True XorOut : FFFFFFFFh Check : E3069283h Here is what I tried- import crcmod f = crcmod.mkCrcFun(0x1EDC6F41) Traceback (most recent call last): File "<stdin>", line 1, in <module> File "C:\Python27\Lib\site-packages

问题 I am trying to use CRC32 to to randomize results in a Sphinx query which already has several nested orders e.g. Select CRC32(Field) as Random from Index Order by Premium,Weight(),Random However, the only unique field I have is a reference . It is an integer so randomizes via CRC32 as 0 . I selected it in my Sphinx Config Select... reference as Randomizer... and then specified it as a string so I could use it in the select: sql_field_string = Randomizer So it would be 'converted' to text.

问题 I need script that will calculate crc32 with the same output for both Python and C. I'm using right now zlib.crc32, but for C there is no such library and we are writing it on our own basing on Wikipedia. But it doesn't return the same value. This is our code of C script (copied from wikipedia, based on RFC): unsigned int crc32( unsigned char *message, unsigned int n ) { //int i, crc; unsigned int crc; unsigned int i; unsigned int byte, c; const unsigned int g0 = 0xEDB88320, g1 = g0>>1, g2 =