|Anthony Wang cd9b330a1f||4 months ago|
|LICENSE||12 months ago|
|README.md||5 months ago|
|sd.c||5 months ago|
|segmenttree.c||4 months ago|
|segmenttree.h||11 months ago|
C port of SD, a very efficient flash cards app
Flash cards are stored in the
cards table of a SQLite database. There are four columns:
idx INTEGER PRIMARY KEY, weight INTEGER, key STRING, val STRING. The
idx is a unique index for each card, starting at 0. The weight is how often the card should come up. The key and value are the front and reverse sides of the card. You can use the
sqlite3 CLI to create a card deck.
Now build this project with
gcc sd.c segmenttree.c -o sd -lsqlite3 -O2 -march=native and run
./sd to enjoy a fast flash cards experience! The program will display the
key of a randomly selected card. Press any key to show the
val of the card. Now press either
n depending on whether you got the card correct, and the program adjusts that card's weight.
If you're wondering where the name came from, this is the C port of SD, which was named after a common type of flash card. 😀
SD is designed to be extremely efficient in order to support a very large number of flash cards and should be able to handle millions of cards with ease. If
N is the number of cards, initializing the program requires
O(N) time and
O(N) memory. Selecting a random card and adjusting its weight requires
O(log N) time. Internally SD uses segment trees to achieve this time complexity.
Some benchmark results using 10 card updates:
C version: ./sd < test Time (mean ± σ): 57.4 ms ± 4.5 ms [User: 6.9 ms, System: 2.4 ms] Range (min … max): 51.9 ms … 70.9 ms 41 runs Go version: ./sd < test Time (mean ± σ): 92.7 ms ± 6.8 ms [User: 8.4 ms, System: 4.5 ms] Range (min … max): 79.4 ms … 108.9 ms 33 runs
The C port is about 30% faster than the original Go code, and I'm currently working on further performance improvements using delayed database writes.