chash.c

// Taken from:
// https://raw.githubusercontent.com/openresty/lua-resty-balancer/refs/heads/master/chash.c

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <assert.h>

#include "chash.h"


#ifndef u_char
#define u_char  unsigned char
#endif

#define CHASH_OK    0
#define CHASH_ERR   -1

#define crc32_final(crc)                                                  \
    crc ^= 0xffffffff


static uint32_t crc32_table256[] = {
    0x00000000, 0x77073096, 0xee0e612c, 0x990951ba,
    0x076dc419, 0x706af48f, 0xe963a535, 0x9e6495a3,
    0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988,
    0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91,
    0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,
    0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,
    0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec,
    0x14015c4f, 0x63066cd9, 0xfa0f3d63, 0x8d080df5,
    0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172,
    0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
    0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940,
    0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,
    0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116,
    0x21b4f4b5, 0x56b3c423, 0xcfba9599, 0xb8bda50f,
    0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
    0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d,
    0x76dc4190, 0x01db7106, 0x98d220bc, 0xefd5102a,
    0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433,
    0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818,
    0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
    0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e,
    0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457,
    0x65b0d9c6, 0x12b7e950, 0x8bbeb8ea, 0xfcb9887c,
    0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,
    0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,
    0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb,
    0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0,
    0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9,
    0x5005713c, 0x270241aa, 0xbe0b1010, 0xc90c2086,
    0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
    0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4,
    0x59b33d17, 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad,
    0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a,
    0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683,
    0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,
    0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1,
    0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe,
    0xf762575d, 0x806567cb, 0x196c3671, 0x6e6b06e7,
    0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc,
    0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
    0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252,
    0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,
    0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60,
    0xdf60efc3, 0xa867df55, 0x316e8eef, 0x4669be79,
    0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
    0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f,
    0xc5ba3bbe, 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04,
    0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,
    0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a,
    0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
    0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38,
    0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21,
    0x86d3d2d4, 0xf1d4e242, 0x68ddb3f8, 0x1fda836e,
    0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,
    0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,
    0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45,
    0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2,
    0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db,
    0xaed16a4a, 0xd9d65adc, 0x40df0b66, 0x37d83bf0,
    0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
    0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6,
    0xbad03605, 0xcdd70693, 0x54de5729, 0x23d967bf,
    0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,
    0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d
};


static inline void
crc32_update(uint32_t *crc, u_char *p, size_t len)
{
    uint32_t  c;

    c = *crc;

    while (len--) {
        c = crc32_table256[(c ^ *p++) & 0xff] ^ (c >> 8);
    }

    *crc = c;
}


static inline void
chash_point_init_crc(chash_point_t *arr, uint32_t start, uint32_t base_hash,
    uint32_t from, uint32_t num, uint32_t id)
{
    chash_point_t *node;
    uint32_t i, hash;
    union {
        uint32_t                        value;
        u_char                          byte[4];
    } prev_hash;

    prev_hash.value = 0;
    node = &arr[start];

    for (i = 0; i < from + num; i++) {
        hash = base_hash;
        crc32_update(&hash, prev_hash.byte, 4);
        crc32_final(hash);

        if (i >= from) {
            node->hash = hash;
            node->id = id;
            node = node + 1;
        }

        /* no big performace different in my test */

        /* this only works when have little endian */
        // prev_hash.value = hash;

        prev_hash.byte[0] = (u_char) (hash & 0xff);
        prev_hash.byte[1] = (u_char) ((hash >> 8) & 0xff);
        prev_hash.byte[2] = (u_char) ((hash >> 16) & 0xff);
        prev_hash.byte[3] = (u_char) ((hash >> 24) & 0xff);
    }
}


void
chash_point_init(chash_point_t *arr, uint32_t base_hash, uint32_t start,
    uint32_t num, uint32_t id)
{
    chash_point_init_crc(arr, start, base_hash, 0, num, id);
}


int
chash_point_sort(chash_point_t arr[], uint32_t n)
{
    chash_point_t *points;
    chash_point_t *node;
    int i, j, index, start, end;
    uint32_t min_sz, m, step;

    /* not sure 1.6 is the best */
    min_sz = n * 1.6;
    m = 2;

    while (m <= min_sz) {
        m *= 2;
    }

    step = pow(2, 32) / m;

    points = (chash_point_t *) calloc(m, sizeof(chash_point_t));
    if (points == NULL) {
        return CHASH_ERR;
    }

    for (i = 0; i < n; i++) {
        node = &arr[i];
        index = node->hash / step;

        assert(index < m); // index must less than m

        for (end = index; end >= 0; end--) {
            if (points[end].id == 0) {
                goto insert;
            }

            if (node->hash >= points[end].hash) {
                break;
            }
        }

        for (start = end - 1; start >= 0; start--) {
            if (points[start].id == 0) {
                /* left shift before end */
                for (j = start; j < end; j++) {
                    points[j].hash = points[j + 1].hash;
                    points[j].id = points[j + 1].id;
                }

                /* points[end] is empty now */

                /* left shift after end when node->hash is bigger than them */
                /* only end == index can match this */
                while (end + 1 < m
                       && points[end + 1].id != 0
                       && points[end + 1].hash < node->hash)
                {
                    points[end].hash = points[end + 1].hash;
                    points[end].id = points[end + 1].id;
                    end += 1;
                }

                goto insert;
            }
        }

        /* full before index, try to append */

        for (end = end + 1; end < m; end++) {
            if (points[end].id == 0) {
                goto insert;
            }

            if (node->hash < points[end].hash) {
                break;
            }
        }

        for (start = end + 1; start < m; start++) {
            if (points[start].id == 0) {
                break;
            }
        }

        /* right shift */
        for (j = start; j > end; j--) {
            points[j].hash = points[j - 1].hash;
            points[j].id = points[j - 1].id;
        }

insert:
        assert(end < m && end >= 0);

        points[end].id = node->id;
        points[end].hash = node->hash;
    }

    j = 0;
    for (i = 0; i < m; i++) {
        if (points[i].id != 0) {
            arr[j].id = points[i].id;
            arr[j].hash = points[i].hash;
            j++;
        }
    }

    free(points);

    return CHASH_OK;
}


int
chash_point_add(chash_point_t *old_points, uint32_t old_length,
    uint32_t base_hash, uint32_t from, uint32_t num, uint32_t id,
    chash_point_t *new_points)
{
    int i, j, k;
    chash_point_t *tmp_points;

    tmp_points = (chash_point_t *) calloc(num, sizeof(chash_point_t));
    if (tmp_points == NULL) {
        return CHASH_ERR;
    }

    chash_point_init_crc(tmp_points, 0, base_hash, from, num, id);

    if (chash_point_sort(tmp_points, num) != CHASH_OK) {
        free(tmp_points);
        return CHASH_ERR;
    }

    j = num - 1;
    k = old_length + num - 1;
    for (i = old_length - 1; i >= 0; i--, k--) {
        while (j >= 0 && tmp_points[j].hash > old_points[i].hash) {
            new_points[k].hash = tmp_points[j].hash;
            new_points[k].id = tmp_points[j].id;

            j--;
            k--;
        }

        new_points[k].hash = old_points[i].hash;
        new_points[k].id = old_points[i].id;
    }

    for (; j >= 0; j--, k--) {
        new_points[k].hash = tmp_points[j].hash;
        new_points[k].id = tmp_points[j].id;
    }

    free(tmp_points);

    return CHASH_OK;
}


int
chash_point_reduce(chash_point_t *old_points, uint32_t old_length,
    uint32_t base_hash, uint32_t from, uint32_t num, uint32_t id)
{
    int i, j, k;
    chash_point_t *tmp_points;

    tmp_points = (chash_point_t *) calloc(num, sizeof(chash_point_t));

    chash_point_init_crc(tmp_points, 0, base_hash, from, num, id);

    if (chash_point_sort(tmp_points, num) != CHASH_OK) {
        free(tmp_points);
        return CHASH_ERR;
    }

    for (i = 0, j = 0, k = 0; i < old_length; i++) {
        if (j < num
            && old_points[i].hash == tmp_points[j].hash
            && old_points[i].id == id)
        {
            j++;
            continue;
        }

        if (i != k) {
            old_points[k].hash = old_points[i].hash;
            old_points[k].id = old_points[i].id;
        }
        k++;
    }

    free(tmp_points);

    return CHASH_OK;
}


void
chash_point_delete(chash_point_t *old_points, uint32_t old_length, uint32_t id)
{
    int i, j;

    for (i = 0, j = 0; i < old_length; i++) {
        if (old_points[i].id == id) {
            continue;
        }

        if (i != j) {
            old_points[j].hash = old_points[i].hash;
            old_points[j].id = old_points[i].id;
        }
        j++;
    }
}