Update README to include information about algorithm used.

More readable.

README.md

@@ -1,38 +1,31 @@
 # Indivisible
 
-Indivisible is an optimized prime number generator and tester written in Rust.
+Indivisible is an optimized prime number generator and tester using a segmented
+version of the [Sieve of
+Eratosthenes](https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes).
 
 ## Build & Installation
 
-To build the project you will require the Rust compiler and build
+Build a binary release using the following command:
-system, `cargo`. At which point you simply run `cargo build` in the root
-directory of the project. To create an optimized release build append
-the `--release` flag to the previous command.
 
-Once a release build has been compiled, you may install Indivisible and
+```console
-the manpage documentation by running the `install` script. In a similar
+$ cargo build -r
-manner, you can run the `uninstall` script to remove the previously
+```
-installed binary and documentation.
 
-## Usage
+Once compiled, you can install it using the `install` script. By default this
+will install to `/usr/local/{bin,share}`, but you can optionally change the
+`PREFIX` used as follows:
 
-The purpose of Indivisible is to find the nth prime and all the primes
+```console
-before it. The basic usage is `indivisible <n>` where `n` is the ordinal
+$ PREFIX="~/.local" ./install
-of the prime you'd like to find. To display all primes before `n`, you
+```
-can run verbose mode by using the `--verbose` or simply `-v` option.
 
-Since Indivisible generates primes using previously computed primes, you
+Additionally there is an `uninstall` script available. If you have used a custom
-can also import prime numbers previously computed with the `--import` or
+`PREFIX` this must also be specified to uninstall in the same manner. To see
-`-i` option. To store already computed primes you are expected to use
+where you've installed it you can always use the following command:
-piping like any UNIX user would expect. Here is an example:
 
-```bash
+```console
-# store first 100 primes in ./primes
+$ which indivisible
-indivisible -v 100 > ./primes
-# appends next 400 primes
-indivisible -i ./primes -v 500 >> ./primes
-# display the 600th prime
-indivisible -i ./primes 600
 ```
 
 ## Legacy

benchmark.sh

@@ -21,6 +21,7 @@ do
 	case "$opt" in
 		s)
 			OPTIONS=("${OPTIONS[@]}" -s "$OPTARG")
+			SIEVE=$OPTARG
 			;;
 		t)
 			TRIALS="$OPTARG"
@@ -33,6 +34,8 @@ do
 done
 
 echo "Calculating primes up to 1,000,000,000"
+echo "Trials: $TRIALS"
+echo "Sieve segment size: ${SIEVE:-"default"}"
 TOTAL="0"
 for _ in $(seq "$TRIALS")
 do

src/worker.rs

@@ -19,6 +19,7 @@
 /**
  * @brief Work on a segment.
  *
+ * @param known_primes:&Vec<u64> List of known primes at least until sqrt(end).
  * @param start:usize Beginning of the segment (inclusive).
  * @param end:usize End of the segment (exclusive).
  *
@@ -28,8 +29,14 @@ pub fn work_segment(known_primes:&Vec<u64>, start:usize, end:usize) -> Vec<u64>
 	let mut sieve = vec![true; end - start];
 	let mut found_primes = Vec::new();
 
+	let sqrt_end = (end as f64).sqrt() as usize;
+
 	for p in known_primes {
 		let prime = *p as usize;
+		if prime > sqrt_end {
+			break;
+		}
+
 		let modu = start % prime;
 		let mut mult = if modu == 0 {
 			start

test.sh

@@ -17,7 +17,7 @@ fi
 tests=0
 passed=0
 
-## TEST 1
+## TEST
 ((tests++))
 echo -n "${tests}: Find all prime numbers before 70..."
 expect="2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 "
@@ -30,7 +30,20 @@ else
 	echo " FAIL"
 fi
 
-## TEST 2
+## TEST
+((tests++))
+echo -n "${tests}: Find last prime before 1,000,000,000..."
+expect="999999937"
+
+if [ "$("$BINARY" 1000000000)" = "$expect" ]
+then
+	echo " pass"
+	((passed++))
+else
+	echo " FAIL"
+fi
+
+## TEST
 ((tests++))
 echo -n "${tests}: 11 is prime..."
 if "$BINARY" -t 11
@@ -41,7 +54,7 @@ else
 	echo " FAIL"
 fi
 
-## TEST 3
+## TEST
 ((tests++))
 echo -n "${tests}: 9 is not prime..."
 if ! "$BINARY" -t 9
@@ -54,3 +67,8 @@ fi
 
 ## RESULTS
 echo "Results: $passed/$tests"
+
+if [ $passed -ne $tests ]
+then
+	exit 1
+fi