/* The following code has been taken directly from
 * draft-ietf-tsvwg-sctpcsum-03.txt
 *
 * The code has now been modified by Werner.Dittmann@t-online.de for use
 * inside the ZRTP implementation.
 */

#include <stdio.h>
#include <stdint.h>
#include <libzrtpcpp/ZrtpCrc32.h>

#define CRC32C_POLY 0x1EDC6F41
#define CRC32C(c,d) (c=(c>>8)^crc_c[(c^(d))&0xFF])
/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
/* Copyright 2001, D. Otis.  Use this program, code or tables    */
/* extracted from it, as desired without restriction.            */
/*                                                               */
/* 32 Bit Reflected CRC table generation for SCTP.               */
/* To accommodate serial byte data being shifted out least       */
/* significant bit first, the table's 32 bit words are reflected */
/* which flips both byte and bit MS and LS positions.  The CRC   */
/* is calculated MS bits first from the perspective of the serial*/
/* stream.  The x^32 term is implied and the x^0 term may also   */
/* be shown as +1.  The polynomial code used is 0x1EDC6F41.      */
/* Castagnoli93                                                  */
/* x^32+x^28+x^27+x^26+x^25+x^23+x^22+x^20+x^19+x^18+x^14+x^13+  */
/* x^11+x^10+x^9+x^8+x^6+x^0                                     */
/* Guy Castagnoli Stefan Braeuer and Martin Herrman              */
/* "Optimization of Cyclic Redundancy-Check Codes                */
/* with 24 and 32 Parity Bits",                                  */
/* IEEE Transactions on Communications, Vol.41, No.6, June 1993  */
/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
static const uint32_t crc_c[256] = {
    0x00000000, 0xF26B8303, 0xE13B70F7, 0x1350F3F4,
    0xC79A971F, 0x35F1141C, 0x26A1E7E8, 0xD4CA64EB,
    0x8AD958CF, 0x78B2DBCC, 0x6BE22838, 0x9989AB3B,
    0x4D43CFD0, 0xBF284CD3, 0xAC78BF27, 0x5E133C24,
    0x105EC76F, 0xE235446C, 0xF165B798, 0x030E349B,
    0xD7C45070, 0x25AFD373, 0x36FF2087, 0xC494A384,
    0x9A879FA0, 0x68EC1CA3, 0x7BBCEF57, 0x89D76C54,
    0x5D1D08BF, 0xAF768BBC, 0xBC267848, 0x4E4DFB4B,
    0x20BD8EDE, 0xD2D60DDD, 0xC186FE29, 0x33ED7D2A,
    0xE72719C1, 0x154C9AC2, 0x061C6936, 0xF477EA35,
    0xAA64D611, 0x580F5512, 0x4B5FA6E6, 0xB93425E5,
    0x6DFE410E, 0x9F95C20D, 0x8CC531F9, 0x7EAEB2FA,
    0x30E349B1, 0xC288CAB2, 0xD1D83946, 0x23B3BA45,
    0xF779DEAE, 0x05125DAD, 0x1642AE59, 0xE4292D5A,
    0xBA3A117E, 0x4851927D, 0x5B016189, 0xA96AE28A,
    0x7DA08661, 0x8FCB0562, 0x9C9BF696, 0x6EF07595,
    0x417B1DBC, 0xB3109EBF, 0xA0406D4B, 0x522BEE48,
    0x86E18AA3, 0x748A09A0, 0x67DAFA54, 0x95B17957,
    0xCBA24573, 0x39C9C670, 0x2A993584, 0xD8F2B687,
    0x0C38D26C, 0xFE53516F, 0xED03A29B, 0x1F682198,
    0x5125DAD3, 0xA34E59D0, 0xB01EAA24, 0x42752927,
    0x96BF4DCC, 0x64D4CECF, 0x77843D3B, 0x85EFBE38,
    0xDBFC821C, 0x2997011F, 0x3AC7F2EB, 0xC8AC71E8,
    0x1C661503, 0xEE0D9600, 0xFD5D65F4, 0x0F36E6F7,
    0x61C69362, 0x93AD1061, 0x80FDE395, 0x72966096,
    0xA65C047D, 0x5437877E, 0x4767748A, 0xB50CF789,
    0xEB1FCBAD, 0x197448AE, 0x0A24BB5A, 0xF84F3859,
    0x2C855CB2, 0xDEEEDFB1, 0xCDBE2C45, 0x3FD5AF46,
    0x7198540D, 0x83F3D70E, 0x90A324FA, 0x62C8A7F9,
    0xB602C312, 0x44694011, 0x5739B3E5, 0xA55230E6,
    0xFB410CC2, 0x092A8FC1, 0x1A7A7C35, 0xE811FF36,
    0x3CDB9BDD, 0xCEB018DE, 0xDDE0EB2A, 0x2F8B6829,
    0x82F63B78, 0x709DB87B, 0x63CD4B8F, 0x91A6C88C,
    0x456CAC67, 0xB7072F64, 0xA457DC90, 0x563C5F93,
    0x082F63B7, 0xFA44E0B4, 0xE9141340, 0x1B7F9043,
    0xCFB5F4A8, 0x3DDE77AB, 0x2E8E845F, 0xDCE5075C,
    0x92A8FC17, 0x60C37F14, 0x73938CE0, 0x81F80FE3,
    0x55326B08, 0xA759E80B, 0xB4091BFF, 0x466298FC,
    0x1871A4D8, 0xEA1A27DB, 0xF94AD42F, 0x0B21572C,
    0xDFEB33C7, 0x2D80B0C4, 0x3ED04330, 0xCCBBC033,
    0xA24BB5A6, 0x502036A5, 0x4370C551, 0xB11B4652,
    0x65D122B9, 0x97BAA1BA, 0x84EA524E, 0x7681D14D,
    0x2892ED69, 0xDAF96E6A, 0xC9A99D9E, 0x3BC21E9D,
    0xEF087A76, 0x1D63F975, 0x0E330A81, 0xFC588982,
    0xB21572C9, 0x407EF1CA, 0x532E023E, 0xA145813D,
    0x758FE5D6, 0x87E466D5, 0x94B49521, 0x66DF1622,
    0x38CC2A06, 0xCAA7A905, 0xD9F75AF1, 0x2B9CD9F2,
    0xFF56BD19, 0x0D3D3E1A, 0x1E6DCDEE, 0xEC064EED,
    0xC38D26C4, 0x31E6A5C7, 0x22B65633, 0xD0DDD530,
    0x0417B1DB, 0xF67C32D8, 0xE52CC12C, 0x1747422F,
    0x49547E0B, 0xBB3FFD08, 0xA86F0EFC, 0x5A048DFF,
    0x8ECEE914, 0x7CA56A17, 0x6FF599E3, 0x9D9E1AE0,
    0xD3D3E1AB, 0x21B862A8, 0x32E8915C, 0xC083125F,
    0x144976B4, 0xE622F5B7, 0xF5720643, 0x07198540,
    0x590AB964, 0xAB613A67, 0xB831C993, 0x4A5A4A90,
    0x9E902E7B, 0x6CFBAD78, 0x7FAB5E8C, 0x8DC0DD8F,
    0xE330A81A, 0x115B2B19, 0x020BD8ED, 0xF0605BEE,
    0x24AA3F05, 0xD6C1BC06, 0xC5914FF2, 0x37FACCF1,
    0x69E9F0D5, 0x9B8273D6, 0x88D28022, 0x7AB90321,
    0xAE7367CA, 0x5C18E4C9, 0x4F48173D, 0xBD23943E,
    0xF36E6F75, 0x0105EC76, 0x12551F82, 0xE03E9C81,
    0x34F4F86A, 0xC69F7B69, 0xD5CF889D, 0x27A40B9E,
    0x79B737BA, 0x8BDCB4B9, 0x988C474D, 0x6AE7C44E,
    0xBE2DA0A5, 0x4C4623A6, 0x5F16D052, 0xAD7D5351,
};


bool zrtpCheckCksum(uint8_t *buffer, uint16_t length, uint32_t crc32)
{
    uint32_t chksum = zrtpGenerateCksum(buffer, length);
    chksum = zrtpEndCksum(chksum);
    // fprintf(stderr, "Received crc %x, computed crc: %x\n", crc32, chksum);
    return (crc32 == chksum);
}

uint32_t zrtpGenerateCksum(uint8_t *buffer, uint16_t length)
{
    uint32_t crc32 = ~(uint32_t) 0;
    uint32_t i;

    // fprintf(stderr, "Buffer %xl, length: %d\n", buffer, length);
    /* Calculate the CRC. */
    for (i = 0; i < length ; i++)
        CRC32C(crc32, buffer[i]);

    return crc32;
}

uint32_t zrtpEndCksum(uint32_t crc32)
{
    uint32_t result;
    uint8_t byte0, byte1, byte2, byte3;

    result = ~crc32;

    /*  result  now holds the negated polynomial remainder;
     *  since the table and algorithm is "reflected" [williams95].
     *  That is,  result has the same value as if we mapped the message
     *  to a polyomial, computed the host-bit-order polynomial
     *  remainder, performed final negation, then did an end-for-end
     *  bit-reversal.
     *  Note that a 32-bit bit-reversal is identical to four inplace
     *  8-bit reversals followed by an end-for-end byteswap.
     *  In other words, the bytes of each bit are in the right order,
     *  but the bytes have been byteswapped.  So we now do an explicit
     *  byteswap.  On a little-endian machine, this byteswap and
     *  the final ntohl cancel out and could be elided.
     */
    byte0 = result & 0xff;
    byte1 = (result>>8) & 0xff;
    byte2 = (result>>16) & 0xff;
    byte3 = (result>>24) & 0xff;

    crc32 = ((byte0 << 24) |
    (byte1 << 16) |
    (byte2 << 8)  |
    byte3);
    // fprintf(stderr, "Computed crc32: %x\n", crc32);
    return crc32;
}