/* SPDX-FileCopyrightText: Lennart Poettering <lennart@poettering.net> */
/* SPDX-License-Identifier: LGPL-2.1-or-later */

#include <math.h>
#include <string.h>
#include <assert.h>
#include <errno.h>

#include "cachunker.h"

/* The hardcoded, maximum chunk size, after which we refuse operation */
#define CA_CHUNK_SIZE_LIMIT_MAX ((size_t) (128U*1024U*1024U))
#define CA_CHUNK_SIZE_LIMIT_MIN ((size_t) 1)

static inline uint32_t rol32(uint32_t x, size_t i) {
        i %= 32;

        if (i == 0) /* Make ubsan happy */
                return x;

        return ((x) << (i)) | ((x) >> (32 - i));
}

static const uint32_t buzhash_table[] = {
        0x458be752, 0xc10748cc, 0xfbbcdbb8, 0x6ded5b68,
        0xb10a82b5, 0x20d75648, 0xdfc5665f, 0xa8428801,
        0x7ebf5191, 0x841135c7, 0x65cc53b3, 0x280a597c,
        0x16f60255, 0xc78cbc3e, 0x294415f5, 0xb938d494,
        0xec85c4e6, 0xb7d33edc, 0xe549b544, 0xfdeda5aa,
        0x882bf287, 0x3116737c, 0x05569956, 0xe8cc1f68,
        0x0806ac5e, 0x22a14443, 0x15297e10, 0x50d090e7,
        0x4ba60f6f, 0xefd9f1a7, 0x5c5c885c, 0x82482f93,
        0x9bfd7c64, 0x0b3e7276, 0xf2688e77, 0x8fad8abc,
        0xb0509568, 0xf1ada29f, 0xa53efdfe, 0xcb2b1d00,
        0xf2a9e986, 0x6463432b, 0x95094051, 0x5a223ad2,
        0x9be8401b, 0x61e579cb, 0x1a556a14, 0x5840fdc2,
        0x9261ddf6, 0xcde002bb, 0x52432bb0, 0xbf17373e,
        0x7b7c222f, 0x2955ed16, 0x9f10ca59, 0xe840c4c9,
        0xccabd806, 0x14543f34, 0x1462417a, 0x0d4a1f9c,
        0x087ed925, 0xd7f8f24c, 0x7338c425, 0xcf86c8f5,
        0xb19165cd, 0x9891c393, 0x325384ac, 0x0308459d,
        0x86141d7e, 0xc922116a, 0xe2ffa6b6, 0x53f52aed,
        0x2cd86197, 0xf5b9f498, 0xbf319c8f, 0xe0411fae,
        0x977eb18c, 0xd8770976, 0x9833466a, 0xc674df7f,
        0x8c297d45, 0x8ca48d26, 0xc49ed8e2, 0x7344f874,
        0x556f79c7, 0x6b25eaed, 0xa03e2b42, 0xf68f66a4,
        0x8e8b09a2, 0xf2e0e62a, 0x0d3a9806, 0x9729e493,
        0x8c72b0fc, 0x160b94f6, 0x450e4d3d, 0x7a320e85,
        0xbef8f0e1, 0x21d73653, 0x4e3d977a, 0x1e7b3929,
        0x1cc6c719, 0xbe478d53, 0x8d752809, 0xe6d8c2c6,
        0x275f0892, 0xc8acc273, 0x4cc21580, 0xecc4a617,
        0xf5f7be70, 0xe795248a, 0x375a2fe9, 0x425570b6,
        0x8898dcf8, 0xdc2d97c4, 0x0106114b, 0x364dc22f,
        0x1e0cad1f, 0xbe63803c, 0x5f69fac2, 0x4d5afa6f,
        0x1bc0dfb5, 0xfb273589, 0x0ea47f7b, 0x3c1c2b50,
        0x21b2a932, 0x6b1223fd, 0x2fe706a8, 0xf9bd6ce2,
        0xa268e64e, 0xe987f486, 0x3eacf563, 0x1ca2018c,
        0x65e18228, 0x2207360a, 0x57cf1715, 0x34c37d2b,
        0x1f8f3cde, 0x93b657cf, 0x31a019fd, 0xe69eb729,
        0x8bca7b9b, 0x4c9d5bed, 0x277ebeaf, 0xe0d8f8ae,
        0xd150821c, 0x31381871, 0xafc3f1b0, 0x927db328,
        0xe95effac, 0x305a47bd, 0x426ba35b, 0x1233af3f,
        0x686a5b83, 0x50e072e5, 0xd9d3bb2a, 0x8befc475,
        0x487f0de6, 0xc88dff89, 0xbd664d5e, 0x971b5d18,
        0x63b14847, 0xd7d3c1ce, 0x7f583cf3, 0x72cbcb09,
        0xc0d0a81c, 0x7fa3429b, 0xe9158a1b, 0x225ea19a,
        0xd8ca9ea3, 0xc763b282, 0xbb0c6341, 0x020b8293,
        0xd4cd299d, 0x58cfa7f8, 0x91b4ee53, 0x37e4d140,
        0x95ec764c, 0x30f76b06, 0x5ee68d24, 0x679c8661,
        0xa41979c2, 0xf2b61284, 0x4fac1475, 0x0adb49f9,
        0x19727a23, 0x15a7e374, 0xc43a18d5, 0x3fb1aa73,
        0x342fc615, 0x924c0793, 0xbee2d7f0, 0x8a279de9,
        0x4aa2d70c, 0xe24dd37f, 0xbe862c0b, 0x177c22c2,
        0x5388e5ee, 0xcd8a7510, 0xf901b4fd, 0xdbc13dbc,
        0x6c0bae5b, 0x64efe8c7, 0x48b02079, 0x80331a49,
        0xca3d8ae6, 0xf3546190, 0xfed7108b, 0xc49b941b,
        0x32baf4a9, 0xeb833a4a, 0x88a3f1a5, 0x3a91ce0a,
        0x3cc27da1, 0x7112e684, 0x4a3096b1, 0x3794574c,
        0xa3c8b6f3, 0x1d213941, 0x6e0a2e00, 0x233479f1,
        0x0f4cd82f, 0x6093edd2, 0x5d7d209e, 0x464fe319,
        0xd4dcac9e, 0x0db845cb, 0xfb5e4bc3, 0xe0256ce1,
        0x09fb4ed1, 0x0914be1e, 0xa5bdb2c3, 0xc6eb57bb,
        0x30320350, 0x3f397e91, 0xa67791bc, 0x86bc0e2c,
        0xefa0a7e2, 0xe9ff7543, 0xe733612c, 0xd185897b,
        0x329e5388, 0x91dd236b, 0x2ecb0d93, 0xf4d82a3d,
        0x35b5c03f, 0xe4e606f0, 0x05b21843, 0x37b45964,
        0x5eff22f4, 0x6027f4cc, 0x77178b3c, 0xae507131,
        0x7bf7cabc, 0xf9c18d66, 0x593ade65, 0xd95ddf11,
};

CaChunker ca_chunker_init = CA_CHUNKER_INIT;

uint32_t ca_chunker_start(CaChunker *c, const void *p, size_t n) {
        const uint8_t *q = p;
        size_t i;

        assert(c);

        assert(CA_CHUNK_SIZE_LIMIT_MIN <= c->chunk_size_min);
        assert(c->chunk_size_min <= c->chunk_size_avg);
        assert(c->chunk_size_avg <= c->chunk_size_max);
        assert(c->chunk_size_max <= CA_CHUNK_SIZE_LIMIT_MAX);

        c->window_size = n;

        for (i = 1; i < n; i++, q++)
                c->h ^= rol32(buzhash_table[*q], n - i);

        c->h ^= buzhash_table[*q];

        return c->h;
}

uint32_t ca_chunker_roll(CaChunker *c, uint8_t leave, uint8_t enter) {

        c->h = rol32(c->h, 1) ^
               rol32(buzhash_table[leave], c->window_size) ^
               buzhash_table[enter];

        return c->h;
}

static bool shall_break(CaChunker *c, uint32_t v) {
        assert(c);

        if (c->chunk_size >= c->chunk_size_max)
                return true;

        if (c->chunk_size < c->chunk_size_min)
                return false;

        return (v % c->discriminator) == (c->discriminator - 1);
}

size_t ca_chunker_scan(CaChunker *c, const void* p, size_t n) {
        const uint8_t *q = p;
        uint32_t v;
        size_t k = 0, idx;

        assert(c);
        assert(p);

        /* Scans the specified bytes for chunk borders. Returns (size_t) -1 if no border was discovered, otherwise the
         * chunk size. */

        if (c->window_size < CA_CHUNKER_WINDOW_SIZE) {
                size_t m;

                /* Append to window to make it full */
                m = CA_CHUNKER_WINDOW_SIZE - c->window_size;
                if (m > n) m = n;

                memcpy(c->window + c->window_size, q, m);
                q += m, n -= m;

                c->window_size += m;
                c->chunk_size += m;

                /* If the window isn't full still, return early */
                if (c->window_size < CA_CHUNKER_WINDOW_SIZE)
                        return (size_t) -1;

                /* Window is full, we are now ready to go. */
                v = ca_chunker_start(c, c->window, c->window_size);
                k = m;

                if (shall_break(c, v))
                        goto now;
        }

        idx = c->chunk_size % CA_CHUNKER_WINDOW_SIZE;

        while (n > 0) {
                v = ca_chunker_roll(c, c->window[idx], *q);
                c->chunk_size++;
                k++;

                if (shall_break(c, v))
                        goto now;

                c->window[idx++] = *q;
                if (idx == CA_CHUNKER_WINDOW_SIZE)
                        idx = 0;

                q++, n--;
        }

        return (size_t) -1;

now:
        c->h = 0;
        c->chunk_size = 0;
        c->window_size = 0;

        return k;
}