checksum

GCC's vector extensions offer a nice, reasonably portable way of accessing some SIMD instructions on different hardware architectures without resorting to hardware specific intrinsics (or auto-vectorization). A real use case, is calculating a simple additive checksum. The one thing that isn't clear is how to safely load data into a vector. typedef char v16qi __attribute__ ((vector_size(16))); static uint8_t checksum(uint8_t *buf, size_t size) { assert(size%16 == 0); uint8_t sum = 0; vec16qi vec = {0}; for (size_t i=0; i<(size/16); i++) { // XXX: Yuck! Is there a better way? vec += *((v16qi*)

I'm trying to add CRC16 error detection to a Motorola HCS08 microcontroller application. My checksums don't match, though. One online CRC calculator provides both the result I see in my PC program and the result I see on the micro. It calls the micro's result "XModem" and the PC's result "Kermit." What is the difference between the way those two ancient protocols specify the use of CRC16? you can implement 16 bit IBM, CCITT, XModem, Kermit, and CCITT 1D0F using the same basic code base. see http://www.acooke.org/cute/16bitCRCAl0.html which uses code from http://www.barrgroup.com/Embedded

I find myself needing to generate a checksum for a string of data, for consistency purposes. The broad idea is that the client can regenerate the checksum based on the payload it recieves and thus detect any corruption that took place in transit. I am vaguely aware that there are all kinds of mathematical principles behind this kind of thing, and that it's very easy for subtle errors to make the whole algorithm ineffective if you try to roll it yourself. So I'm looking for advice on a hashing/checksum algorithm with the following criteria: It will be generated by Javascript, so needs to be

When calculating a single MD5 checksum on a large file, what technique is generally used to combine the various MD5 values into a single value? Do you just add them together? I'm not really interested in any particular language, library or API which will do this; rather I'm just interested in the technique behind it. Can someone explain how it is done? Given the following algorithm in pseudo-code: MD5Digest X for each file segment F MD5Digest Y = CalculateMD5(F) Combine(X,Y) But what exactly would Combine do? Does it add the two MD5 digests together, or what? In order to calculate MD5 values

I have heard that when creating a hash, it's possible that if small files or amounts of data are used, the resulting hash is more likely to suffer from a collision. If that is true, is there a minimum "safe" amount of data that should be used to ensure this doesn't happen? I guess the question could also be phrased as: What is the smallest amount of data that can be safely and securely hashed? A hash function accepts inputs of arbitrary (or at least very high) length, and produces a fixed-length output. There are more possible inputs than possible outputs, so collisions must exist. The whole

I need a quick checksum (as fast as possilbe) for small strings (20-500 chars). I need the source code and that must be small! (about 100 LOC max) If it could generate strings in Base32/64. (or something similar) it would be perfect. Basically the checksums cannot use any "bad" chars.. you know.. the usual (){}[].,;:/+-\| etc Clarifications It could be strong/weak, that really doesn't matter since it is only for behind-the-scenes purposes. It need not contain all the data of the original string since I will be only doing comparison with generated checksums, I don't expect any sort of

I am using Java to generate the MD5 hash for some files. I need to generate one MD5 for several files with a total size of about 1 gigabyte. Here's my code: private String generateMD5(SequenceInputStream inputStream){ if(inputStream==null){ return null; } MessageDigest md; try { int read =0; byte[] buf = new byte[2048]; md = MessageDigest.getInstance("MD5"); while((read = inputStream.read(buf))>0){ md.update(buf,0,read); } byte[] hashValue = md.digest(); return new String(hashValue); } catch (NoSuchAlgorithmException e) { return null; } catch (IOException e) { return null; }finally{ try { if