mmask.c

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/*
 * qrencode - QR Code encoder
 *
 * Masking for Micro QR Code.
 * Copyright (C) 2006-2017 Kentaro Fukuchi <kentaro@fukuchi.org>
 *
 * This library 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 2.1 of the License, or any later version.
 *
 * This library 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 this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include "config.h"
#include <stdlib.h>
#include <string.h>
#include <limits.h>
#include <errno.h>

#include "qrencode.h"
#include "mqrspec.h"
#include "mmask.h"

STATIC_IN_RELEASE void MMask_writeFormatInformation(int version, int width, unsigned char *frame, int mask, QRecLevel level)
{
    unsigned int format;
    unsigned char v;
    int i;

    format = MQRspec_getFormatInfo(mask, version, level);

    for(i = 0; i < 8; i++) {
        v = 0x84 | (format & 1);
        frame[width * (i + 1) + 8] = v;
        format = format >> 1;
    }
    for(i = 0; i < 7; i++) {
        v = 0x84 | (format & 1);
        frame[width * 8 + 7 - i] = v;
        format = format >> 1;
    }
}

#define MASKMAKER(__exp__) \
    int x, y;\
\
    for(y = 0; y < width; y++) {\
        for(x = 0; x < width; x++) {\
            if(*s & 0x80) {\
                *d = *s;\
            } else {\
                *d = *s ^ ((__exp__) == 0);\
            }\
            s++; d++;\
        }\
    }

static void Mask_mask0(int width, const unsigned char *s, unsigned char *d)
{
    MASKMAKER(y&1)
}

static void Mask_mask1(int width, const unsigned char *s, unsigned char *d)
{
    MASKMAKER(((y/2)+(x/3))&1)
}

static void Mask_mask2(int width, const unsigned char *s, unsigned char *d)
{
    MASKMAKER((((x*y)&1)+(x*y)%3)&1)
}

static void Mask_mask3(int width, const unsigned char *s, unsigned char *d)
{
    MASKMAKER((((x+y)&1)+((x*y)%3))&1)
}

#define maskNum (4)
typedef void MaskMaker(int, const unsigned char *, unsigned char *);
static MaskMaker *maskMakers[maskNum] = {
    Mask_mask0, Mask_mask1, Mask_mask2, Mask_mask3
};

#ifdef WITH_TESTS
unsigned char *MMask_makeMaskedFrame(int width, unsigned char *frame, int mask)
{
    unsigned char *masked;

    masked = (unsigned char *)malloc((size_t)(width * width));
    if(masked == NULL) return NULL;

    maskMakers[mask](width, frame, masked);

    return masked;
}
#endif

unsigned char *MMask_makeMask(int version, unsigned char *frame, int mask, QRecLevel level)
{
    unsigned char *masked;
    int width;

    if(mask < 0 || mask >= maskNum) {
        errno = EINVAL;
        return NULL;
    }

    width = MQRspec_getWidth(version);
    masked = (unsigned char *)malloc((size_t)(width * width));
    if(masked == NULL) return NULL;

    maskMakers[mask](width, frame, masked);
    MMask_writeFormatInformation(version, width, masked, mask, level);

    return masked;
}

STATIC_IN_RELEASE int MMask_evaluateSymbol(int width, unsigned char *frame)
{
    int x, y;
    unsigned char *p;
    int sum1 = 0, sum2 = 0;

    p = frame + width * (width - 1);
    for(x = 1; x < width; x++) {
        sum1 += (p[x] & 1);
    }

    p = frame + width * 2 - 1;
    for(y = 1; y < width; y++) {
        sum2 += (*p & 1);
        p += width;
    }

    return (sum1 <= sum2)?(sum1 * 16 + sum2):(sum2 * 16 + sum1);
}

unsigned char *MMask_mask(int version, unsigned char *frame, QRecLevel level)
{
    int i;
    unsigned char *mask, *bestMask;
    int maxScore = 0;
    int score;
    int width;

    width = MQRspec_getWidth(version);

    mask = (unsigned char *)malloc((size_t)(width * width));
    if(mask == NULL) return NULL;
    bestMask = NULL;

    for(i = 0; i < maskNum; i++) {
        score = 0;
        maskMakers[i](width, frame, mask);
        MMask_writeFormatInformation(version, width, mask, i, level);
        score = MMask_evaluateSymbol(width, mask);
        if(score > maxScore) {
            maxScore = score;
            free(bestMask);
            bestMask = mask;
            mask = (unsigned char *)malloc((size_t)(width * width));
            if(mask == NULL) break;
        }
    }
    free(mask);
    return bestMask;
}