Add n_free_blocks() option

[vbkaisetsu]

This branch removes the following constants:

• INIT_CAPACITY: states is initialized by with_capacity() with this value, but it is often reallocated for a large automaton. On the other hand, this capacity is too large for small devices.
• FREE_BLOCKS and FREE_STATES: Some small devices do not have enough memory, so I added an option to change these parameters.

[kampersanda]

Thank you for your update.

As I commented, making FREE_BLOCKS smaller does not necessarily mean that the memory usage will be smaller.
However, a large extras should not be allocated in stack memory, and I agree with the modification.

[vbkaisetsu]

I am using a tiny machine that has just a few amount of the memory.

In this machine, num_free_blocks=16 is too large to construct an automaton, so I added a new description.

This is an example. In this environment, num_free_blocks must be smaller than or equal to 11.

#![feature(alloc_error_handler)]
#![no_main]
#![no_std]

use panic_halt as _;

use core::alloc::Layout;

use alloc_cortex_m::CortexMHeap;
use cortex_m_rt::entry;
use cortex_m_semihosting::{hprintln, debug};

#[global_allocator]
static ALLOCATOR: CortexMHeap = CortexMHeap::empty();

const HEAP_SIZE: usize = 40 * 1024; // 40 KiB

#[entry]
fn main() -> ! {
    unsafe { ALLOCATOR.init(cortex_m_rt::heap_start() as usize, HEAP_SIZE) }

    let patterns = &["this", "is", "a", "test"];

    let pma = daachorse::DoubleArrayAhoCorasickBuilder::new().num_free_blocks(16).build(patterns);

    if pma.is_ok() {
        hprintln!("OK!").unwrap();
    } else {
        hprintln!("ERROR!").unwrap();
    }

    debug::exit(debug::EXIT_SUCCESS);

    loop {}
}

#[alloc_error_handler]
fn alloc_error(_layout: Layout) -> ! {
    hprintln!("<<< allocation error >>>").unwrap();
    loop {}
}

$ qemu-system-arm -cpu cortex-m3 -machine lm3s6965evb -nographic -semihosting-config enable=on,target=native -kernel target/thumbv7m-none-eabi/release/daachorse-lm3s6965evb
Timer with period zero, disabling
<<< allocation error >>>