checksum

Checksum for a SQLite database?

由 我的未来我决定 提交于 2019-12-07 18:02:00
问题 I'd like to be able to tell whether a SQLite database file has been updated in any way. How would I go about implementing that? The first solution I think of is comparing checksums, but I don't really have any experience working with checksums. 回答1: According to http://www.sqlite.org/fileformat.html SQLite3 maintains a file change counter in byte 24..27 of the database file. It is independent of the file change time which, for example, can change after a binary restore or rollback while

Best 8-bit supplemental checksum for CRC8-protected packet

由 天大地大妈咪最大 提交于 2019-12-07 15:36:22
问题 I'm looking at designing a low-level radio communications protocol, and am trying to decide what sort of checksum/crc to use. The hardware provides a CRC-8; each packet has 6 bytes of overhead in addition to the data payload. One of the design goals is to minimize transmission overhead. For some types of data, the CRC-8 should be adequate, for for other types it would be necessary to supplement that to avoid accepting erroneous data. If I go with a single-byte supplement, what would be the

Is Fletchers16 checksum suitable for small data?

由 生来就可爱ヽ(ⅴ＜●) 提交于 2019-12-07 13:21:58
问题 Using the straight forward implementation on wikipedia Fletcher's checksum we get the same checksum for data such as "BCA" and "CAB" as well as "BAC" and "ACB". Is this expected? Should not the Fletcher16 checksum account for the order of the blocks? The deficiency can easily be fixed by OR'ing the index with the data as shown in the code below.... uint16_t fletcher16( uint8_t *data, int count ) { uint16_t sum1 = 0; uint16_t sum2 = 0; int index; for( index = 0; index < count; ++index ) { /

Can this checksum algorithm be improved?

由 末鹿安然 提交于 2019-12-07 08:39:07
问题 We have a very old, unsupported program which copies files across SMB shares. It has a checksum algorithm to determine if the file contents have changed before copying. The algorithm seems easily fooled -- we've just found an example where two files, identical except a single '1' changing to a '2', return the same checksum. Here's the algorithm: unsigned long GetFileCheckSum(CString PathFilename) { FILE* File; unsigned long CheckSum = 0; unsigned long Data = 0; unsigned long Count = 0; if (

Checking the error detection capabilities of CRC polynomials

由 老子叫甜甜 提交于 2019-12-07 07:27:15
问题 I tried to find out how to calculate the error detection capabilities of arbitrary CRC polynomials. I know that there are various error detection capabilities that may (or may not) apply to an arbitrary polynomial: Detection of a single bit error: All CRCs can do this since this only requires a CRC width >= 1. Detection of burst errors: All CRCs can detect burst errors up to a size that equals their width. Detection of odd numbers of bit errors: CRC with polynomials with an even number of

Generate Running Hash (or Checksum) in C#?

由 心已入冬 提交于 2019-12-07 07:02:57
问题 Preface: I am doing a data-import that has a verify-commit phase. The idea is that: the first phase allows taking data from various sources and then running various insert/update/validate operations on a database. The commit is rolled back but a "verification hash/checksum" is generated. The commit phase is the same, but, if the "verification hash/checksum" is the same then the operations will be committed. (The database will be running under the appropriate isolation levels.) Restrictions:

checksum calculation

由 感情迁移 提交于 2019-12-07 06:58:28
To calculate CRC I found a piece of code but I am not understanding the concept. Here is the code: count =128 and ptr=some value; calcrc(unsigned char *ptr, int count) { unsigned short crc; unsigned char i; crc = 0; while (--count >= 0) { crc = crc ^ (unsigned short)*ptr++ << 8; i = 8; do { if (crc & 0x8000) crc = crc << 1 ^ 0x1021; else crc = crc << 1; } while(--i); } return (crc); } Please any body explain and tell me the logic. This looks like a CRC (specifically it looks like CRC-16-CCITT, used by things like 802.15.4, X.25, V.41, CDMA, Bluetooth, XMODEM, HDLC, PPP and IrDA). You might

Current version of data in database has changed since user initiated update process

由 蹲街弑〆低调 提交于 2019-12-06 15:51:30
问题 I have a Master Detail form in my Oracle APEX application. When I am trying to update data in this form, I am getting below error. Current version of data in database has changed since user initiated update process. current row version identifier = "26D0923D8A5144D6F483C2B9815D07D3" application row version identifier = "1749BCD159359424E1EE00AC1C3E3FCB" (Row 1) I have cleared browser cache and try to update. But it not worked. How can I solve this? 回答1: I have experienced similar problem

Ansible: How to Check a local and remote set of files for sha1 checksum

由 淺唱寂寞╮ 提交于 2019-12-06 13:27:22
问题 I want to be able to do a checksum based on a list of files in a local dir. Then be able to get those files checksum and compare it to the checksum of the same files on a remote system. I know I can get the with the following # Local File - stat: path: "{{ playbook_dir }}/roles/common/files/myfile.dat" checksum_algorithm: sha1 delegate_to: localhost run_once: true register: localsha_result # Remote file - stat: path: "{{ rmt_dest_dir }}/myfile.dat" checksum_algorithm: sha1 register: sha

Calculate an Internet (aka IP, aka RFC791) checksum in C#

由 空扰寡人 提交于 2019-12-06 12:20:38
Interestingly, I can find implementations for the Internet Checksum in almost every language except C#. Does anyone have an implementation to share? Remember, the internet protocol specifies that: "The checksum field is the 16 bit one's complement of the one's complement sum of all 16 bit words in the header. For purposes of computing the checksum, the value of the checksum field is zero." More explanation can be found from Dr. Math . There are some efficiency pointers available, but that's not really a large concern for me at this point. Please include your tests! (Edit: Valid comment
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