bitstring.c

/*
    bitstring.c -- functions for handling bitstrings.

    fgen -- Library for optimization using a genetic algorithm or particle swarm optimization.
    Copyright 2012, Harm Hanemaaijer

    This file is part of fgen.

    fgen is free software: you can redistribute it and/or modify it
    under the terms of the GNU Lesser General Public License as published
    by the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    fgen is distributed in the hope that it will be useful, but WITHOUT
    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
    License for more details.

    You should have received a copy of the GNU Lesser General Public
    License along with fgen.  If not, see <http://www.gnu.org/licenses/>.

*/


#include <stdlib.h>
#include <stdint.h>
#include <limits.h>
#include <fgen.h>
#include <random.h>

#if __WORDSIZE == 64
#define POINTER_TO_UINT(x) ((unsigned long int)(x))
#else
#define POINTER_TO_UINT(x) ((unsigned int)(x))
#endif

void CreateRandomBitstring(FgenRNG *rng, unsigned char *bitstring, int size_in_bytes) {
        while (size_in_bytes >= 1 && (POINTER_TO_UINT(bitstring) & 3) != 0) {
                *bitstring = fgen_random_8(rng);
                size_in_bytes--;
                bitstring++;
        }
        while (size_in_bytes >= 4) {
                *(unsigned int *)bitstring = fgen_random_32(rng);
                size_in_bytes -= 4;
                bitstring += 4;
        }
        while (size_in_bytes >= 1) {
                *bitstring = fgen_random_8(rng);
                size_in_bytes--;
                bitstring++;
        }
}

static void fgen_set_random_bit(FgenRNG *rng, unsigned char *bitstring, const int offset) {
    bitstring[offset / 8] &= 0xFF ^ (1 << (offset & 7));
    bitstring[offset / 8] |= fgen_random_2(rng) << (offset & 7);
}

void fgen_set_random_bitstring(FgenRNG *rng, unsigned char *bitstring, int offset, int nu_bits) {
    int i;
    if (nu_bits == 1) {
         fgen_set_random_bit(rng, bitstring, offset);
         return;
    }
    /* Fast case when offset and nu_bits are a multiple of 8. */
    if ((offset & 7) == 0 && (nu_bits & 7) == 0) {
        CreateRandomBitstring(rng, bitstring + offset / 8, nu_bits / 8);
        return;
    }
    for (i = offset; i < offset + nu_bits; i++)
        fgen_set_random_bit(rng, bitstring, i);
}

void fgen_mutate_bit(unsigned char *bitstring, int bitnumber) {
        bitstring[bitnumber / 8] ^= 1 << (bitnumber & 7);
}

int fgen_get_bit(const unsigned char *bitstring, int bitnumber) {
        return (bitstring[bitnumber / 8] & (1 << (bitnumber & 7))) >> (bitnumber & 7);
}


void fgen_copy_partial_bitstring(const unsigned char *src, unsigned char *dest, int bitoffset, int number_of_bits) {
        int i, offset;
        if (number_of_bits == 0)
                return;
        offset = bitoffset / 8;
        if ((bitoffset & 7) != 0) {
                for (i = bitoffset & 7; i < 8; i++) {
                        dest[offset] &= ~(1 << i);
                        dest[offset] |= src[offset] & (1 << i);
                        number_of_bits--;
                        if (number_of_bits == 0)
                                return;
                }
                offset++;
        }
        while (number_of_bits >= 8 && (POINTER_TO_UINT(&dest[offset]) & 3) != 0) {
                dest[offset] = src[offset];
                number_of_bits -= 8;
                offset++;
        }
        while (number_of_bits >= 32) {
                *(unsigned int *)&dest[offset] = *(unsigned int *)&src[offset];
                number_of_bits -= 32;
                offset += 4;
        }
        while (number_of_bits >= 8) {
                dest[offset] = src[offset];
                number_of_bits -= 8;
                offset++;
        }
        for (i = 0; i < number_of_bits; i++) {
                dest[offset] &= ~(1 << i);
                dest[offset] |= src[offset] & (1 << i);
        }
}