One of the finer pieces of code I have ever written

raid.h

#ifndef _RAID_H_
#define _RAID_H_

#define RAID_LEVEL 3
#define RAID_WRITE(stat) do {int raidi; for(raidi = 0; raidi < RAID_LEVEL; ++raidi) stat;} while(0)
#define raidwr raid[raidi]
#define raidrd raid[0]

GlobalState raid[RAID_LEVEL];

static void raid_init() {
    RAID_WRITE(bzero(&raidwr, sizeof(raidwr)));
}

static unsigned int raid_hash(unsigned char *data, int size) {
    int hash = 1;
    unsigned char *end = data + size;
    for(; data < end; data++)
        hash = hash * 31 + *data;
    return hash;
}

static int raid_find_bad() {
    int hash[3];
    hash[0] = raid_hash(&raid[0], sizeof(raid[0]));
    hash[1] = raid_hash(&raid[1], sizeof(raid[0]));
    hash[2] = raid_hash(&raid[2], sizeof(raid[0]));
    if (hash[0] == hash[1])
        if (hash[1] == hash[2])
            return -1;
        else
            return 2;
    else
        if (hash[0] == hash[2])
            return 1;
        else if (hash[1] == hash[2])
            return 0;
    return -2;
}

static void raid_check() {
    int bad = raid_find_bad();
    int good = (bad > 0 ? 0 : (bad == 0 ? 1 : -1));
    if (bad == -1)
        return;
    if (bad == -2) {
        trprintf(LOG_ERRORS, "All three copies of global state have been corrupted. Stop.\n");
        printf("All three copies of global state have been corrupted. Stop.\n");
        fflush(stdout);
        abort();
    }
    memcpy(&raid[bad], &raid[good], sizeof(raid[0]));
    trprintf(LOG_ERRORS, "WARNING! Successfully survived a memory corruption (of state copy #%d)\n", bad);
    printf("WARNING! Successfully survived a memory corruption (of state copy #%d)\n", bad);
    fflush(stdout);
}

#define raid_verify() raid_verify_(__FILE__, __LINE__)
static void raid_verify_(const char *file, int line) {
    int bad = raid_find_bad();
    if (bad == -1)
        return;
    if (bad == -2) {
        trprintf(LOG_ERRORS, "All three copies of global state have been corrupted by %s:%d\n", file, line);
        printf("All three copies of global state have been corrupted by %s:%d\n", file, line);
    } else {
        trprintf(LOG_ERRORS, "Copy of global state #%d has been corrupted by %s:%d\n", bad, file, line);
        printf("Copy of global state #%d has been corrupted by %s:%d\n", bad, file, line);
        raid_check();
    }
    fflush(stdout);
}

#endif