/* crc32.c -- compute the CRC-32 of a data stream
 * Copyright (C) 1995-2022 Mark Adler
 * For conditions of distribution and use, see copyright notice in zlib.h
 *
 * This interleaved implementation of a CRC makes use of pipelined multiple
 * arithmetic-logic units, commonly found in modern CPU cores. It is due to
 * Kadatch and Jenkins (2010). See doc/crc-doc.1.0.pdf in this distribution.
 */

/* @(#) $Id$ */

/*
  Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore
  protection on the static variables used to control the first-use generation
  of the crc tables. Therefore, if you #define DYNAMIC_CRC_TABLE, you should
  first call get_crc_table() to initialize the tables before allowing more than
  one thread to use crc32().

  MAKECRCH can be #defined to write out crc32.h. A main() routine is also
  produced, so that this one source file can be compiled to an executable.
 */
#include <stdint.h>
#include <stdlib.h>

#define __USE_LARGEFILE64
#include <sys/types.h>

#if (defined(__HAIKU__) || defined(__unix__) || defined(__APPLE__)) && !defined(__linux__)
#    define off64_t  off_t
#endif

#ifdef MAKECRCH
#  include <stdio.h>
#  ifndef DYNAMIC_CRC_TABLE
#    define DYNAMIC_CRC_TABLE
#  endif /* !DYNAMIC_CRC_TABLE */
#endif /* MAKECRCH */

 /*
  A CRC of a message is computed on N braids of words in the message, where
  each word consists of W bytes (4 or 8). If N is 3, for example, then three
  running sparse CRCs are calculated respectively on each braid, at these
  indices in the array of words: 0, 3, 6, ..., 1, 4, 7, ..., and 2, 5, 8, ...
  This is done starting at a word boundary, and continues until as many blocks
  of N * W bytes as are available have been processed. The results are combined
  into a single CRC at the end. For this code, N must be in the range 1..6 and
  W must be 4 or 8. The upper limit on N can be increased if desired by adding
  more #if blocks, extending the patterns apparent in the code. In addition,
  crc32.h would need to be regenerated, if the maximum N value is increased.

  N and W are chosen empirically by benchmarking the execution time on a given
  processor. The choices for N and W below were based on testing on Intel Kaby
  Lake i7, AMD Ryzen 7, ARM Cortex-A57, Sparc64-VII, PowerPC POWER9, and MIPS64
  Octeon II processors. The Intel, AMD, and ARM processors were all fastest
  with N=5, W=8. The Sparc, PowerPC, and MIPS64 were all fastest at N=5, W=4.
  They were all tested with either gcc or clang, all using the -O3 optimization
  level. Your mileage may vary.
 */

/* Define N */
#ifdef Z_TESTN
#  define N Z_TESTN
#else
#  define N 5
#endif
#if N < 1 || N > 6
#  error N must be in 1..6
#endif

/*
  crc_t must be at least 32 bits. word_t must be at least as long as
  crc_t. It is assumed here that word_t is either 32 bits or 64 bits, and
  that bytes are eight bits.
 */

/*
  Define W and the associated word_t type. If W is not defined, then a
  braided calculation is not used, and the associated tables and code are not
  compiled.
 */
#ifdef CDROM_TESTW
#  if CDROM_TESTW-1 != -1
#    define W CDROM_TESTW
#  endif
#else
#  ifdef MAKECRCH
#    define W 8         /* required for MAKECRCH */
#  else
#    if defined(__x86_64__) || defined(__aarch64__)
#      define W 8
#    else
#      define W 4
#    endif
#  endif
#endif
#ifdef W
#  if W == 8
     typedef uint64_t word_t;
#  else
#    undef W
#    define W 4
     typedef uint32_t word_t;
#  endif
#endif

/*
   #ifdef this out because that code path does not currently produce the
   correct results.
 */
#ifdef USE_ARMCRC32
/* If available, use the ARM processor CRC32 instruction. */
#if defined(__aarch64__) && defined(__ARM_FEATURE_CRC32) && W == 8
#  define ARMCRC32
#endif
#endif

#if defined(W) && (!defined(ARMCRC32) || defined(DYNAMIC_CRC_TABLE))
/*
   Swap the bytes in a word_t to convert between little and big endian. Any
   self-respecting compiler will optimize this to a single machine byte-swap
   instruction, if one is available. This assumes that word_t is either 32 bits
   or 64 bits.
 */
static word_t byte_swap(word_t word) {
#  if W == 8
    return
        (word & 0xff00000000000000) >> 56 |
        (word & 0xff000000000000) >> 40 |
        (word & 0xff0000000000) >> 24 |
        (word & 0xff00000000) >> 8 |
        (word & 0xff000000) << 8 |
        (word & 0xff0000) << 24 |
        (word & 0xff00) << 40 |
        (word & 0xff) << 56;
#  else   /* W == 4 */
    return
        (word & 0xff000000) >> 24 |
        (word & 0xff0000) >> 8 |
        (word & 0xff00) << 8 |
        (word & 0xff) << 24;
#  endif
}
#endif

#ifdef DYNAMIC_CRC_TABLE
/* =========================================================================
 * Table of powers of x for combining CRC-32s, filled in by make_crc_table()
 * below.
 */
   static crc_t x2n_table[32];
#else
/* =========================================================================
 * Tables for byte-wise and braided CRC-32 calculations, and a table of powers
 * of x for combining CRC-32s, all made by make_crc_table().
 */
#  include "crc32.h"
#endif

/* CRC polynomial. */
// #define POLY 0xedb88320         /* p(x) reflected, with x^32 implied */
#define POLY 0xd8018001         /* p(x) reflected, with x^32 implied */

#ifdef DYNAMIC_CRC_TABLE
/* =========================================================================
 * Build the tables for byte-wise and braided CRC-32 calculations, and a table
 * of powers of x for combining CRC-32s.
 */
static crc_t crc_table[256];
#ifdef W
   static word_t crc_big_table[256];
   static crc_t crc_braid_table[W][256];
   static word_t crc_braid_big_table[W][256];
   static void braid(crc_t [][256], word_t [][256], int, int);
#endif
#ifdef MAKECRCH
   static void write_table(FILE *, const crc_t *, int);
   static void write_table32hi(FILE *, const word_t *, int);
   static void write_table64(FILE *, const word_t *, int);
#endif /* MAKECRCH */

/*
  Define a once() function depending on the availability of atomics. If this is
  compiled with DYNAMIC_CRC_TABLE defined, and if CRCs will be computed in
  multiple threads, and if atomics are not available, then get_crc_table() must
  be called to initialize the tables and must return before any threads are
  allowed to compute or combine CRCs.
 */

/* Definition of once functionality. */
typedef struct once_s once_t;

/* Check for the availability of atomics. */
#if defined(__STDC__) && __STDC_VERSION__ >= 201112L && \
    !defined(__STDC_NO_ATOMICS__)

#include <stdatomic.h>

/* Structure for once(), which must be initialized with ONCE_INIT. */
struct once_s {
    atomic_flag begun;
    atomic_int done;
};
#define ONCE_INIT {ATOMIC_FLAG_INIT, 0}

/*
  Run the provided init() function exactly once, even if multiple threads
  invoke once() at the same time. The state must be a once_t initialized with
  ONCE_INIT.
 */
static void once(once_t *state, void (*init)(void)) {
    if (!atomic_load(&state->done)) {
        if (atomic_flag_test_and_set(&state->begun))
            while (!atomic_load(&state->done))
                ;
        else {
            init();
            atomic_store(&state->done, 1);
        }
    }
}

#else   /* no atomics */

/* Structure for once(), which must be initialized with ONCE_INIT. */
struct once_s {
    volatile int begun;
    volatile int done;
};
#define ONCE_INIT {0, 0}

/* Test and set. Alas, not atomic, but tries to minimize the period of
   vulnerability. */
static int test_and_set(int volatile *flag) {
    int was;

    was = *flag;
    *flag = 1;
    return was;
}

/* Run the provided init() function once. This is not thread-safe. */
static void once(once_t *state, void (*init)(void)) {
    if (!state->done) {
        if (test_and_set(&state->begun))
            while (!state->done)
                ;
        else {
            init();
            state->done = 1;
        }
    }
}

#endif

/* State for once(). */
static once_t made = ONCE_INIT;

/*
  Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
  x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x+1.

  Polynomials over GF(2) are represented in binary, one bit per coefficient,
  with the lowest powers in the most significant bit. Then adding polynomials
  is just exclusive-or, and multiplying a polynomial by x is a right shift by
  one. If we call the above polynomial p, and represent a byte as the
  polynomial q, also with the lowest power in the most significant bit (so the
  byte 0xb1 is the polynomial x^7+x^3+x^2+1), then the CRC is (q*x^32) mod p,
  where a mod b means the remainder after dividing a by b.

  This calculation is done using the shift-register method of multiplying and
  taking the remainder. The register is initialized to zero, and for each
  incoming bit, x^32 is added mod p to the register if the bit is a one (where
  x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by x
  (which is shifting right by one and adding x^32 mod p if the bit shifted out
  is a one). We start with the highest power (least significant bit) of q and
  repeat for all eight bits of q.

  The table is simply the CRC of all possible eight bit values. This is all the
  information needed to generate CRCs on data a byte at a time for all
  combinations of CRC register values and incoming bytes.
 */

static void make_crc_table(void) {
    unsigned i, j, n;
    crc_t    p;

    /* initialize the CRC of bytes tables */
    for (i = 0; i < 256; i++) {
        p = i;
        for (j = 0; j < 8; j++)
            p = p & 1 ? (p >> 1) ^ POLY : p >> 1;
        crc_table[i] = p;
#ifdef W
        crc_big_table[i] = byte_swap(p);
#endif
    }

    /* initialize the x^2^n mod p(x) table */
    p = (crc_t) 1 << 30;         /* x^1 */
    x2n_table[0] = p;
    for (n = 1; n < 32; n++)
        x2n_table[n] = p = multmodp(p, p);

#ifdef W
    /* initialize the braiding tables -- needs x2n_table[] */
    braid(crc_braid_table, crc_braid_big_table, N, W);
#endif

#ifdef MAKECRCH
    {
        /*
           The crc32.h header file contains tables for both 32-bit and 64-bit
           word_t's, and so requires a 64-bit type be available. In that
           case, word_t must be defined to be 64-bits. This code then also
           generates and writes out the tables for the case that word_t is
           32 bits.
         */
#if !defined(W) || W != 8
#  error Need a 64-bit integer type in order to generate crc32.h.
#endif
        FILE *out;
        int k, n;
        crc_t ltl[8][256];
        word_t big[8][256];

        out = fopen("crc32.h", "w");
        if (out == NULL) return;

        /* write out little-endian CRC table to crc32.h */
        fprintf(out,
            "/* crc32.h -- tables for rapid CRC calculation\n"
            " * Generated automatically by crc32.c\n */\n"
            "\n"
            "static const crc_t crc_table[] = {\n"
            "    ");
        write_table(out, crc_table, 256);
        fprintf(out,
            "};\n");

        /* write out big-endian CRC table for 64-bit word_t to crc32.h */
        fprintf(out,
            "\n"
            "#ifdef W\n"
            "\n"
            "#if W == 8\n"
            "\n"
            "static const word_t crc_big_table[] = {\n"
            "    ");
        write_table64(out, crc_big_table, 256);
        fprintf(out,
            "};\n");

        /* write out big-endian CRC table for 32-bit word_t to crc32.h */
        fprintf(out,
            "\n"
            "#else /* W == 4 */\n"
            "\n"
            "static const word_t crc_big_table[] = {\n"
            "    ");
        write_table32hi(out, crc_big_table, 256);
        fprintf(out,
            "};\n"
            "\n"
            "#endif\n");

        /* write out braid tables for each value of N */
        for (n = 1; n <= 6; n++) {
            fprintf(out,
            "\n"
            "#if N == %d\n", n);

            /* compute braid tables for this N and 64-bit word_t */
            braid(ltl, big, n, 8);

            /* write out braid tables for 64-bit word_t to crc32.h */
            fprintf(out,
            "\n"
            "#if W == 8\n"
            "\n"
            "static const crc_t crc_braid_table[][256] = {\n");
            for (k = 0; k < 8; k++) {
                fprintf(out, "   {");
                write_table(out, ltl[k], 256);
                fprintf(out, "}%s", k < 7 ? ",\n" : "");
            }
            fprintf(out,
            "};\n"
            "\n"
            "static const word_t crc_braid_big_table[][256] = {\n");
            for (k = 0; k < 8; k++) {
                fprintf(out, "   {");
                write_table64(out, big[k], 256);
                fprintf(out, "}%s", k < 7 ? ",\n" : "");
            }
            fprintf(out,
            "};\n");

            /* compute braid tables for this N and 32-bit word_t */
            braid(ltl, big, n, 4);

            /* write out braid tables for 32-bit word_t to crc32.h */
            fprintf(out,
            "\n"
            "#else /* W == 4 */\n"
            "\n"
            "static const crc_t crc_braid_table[][256] = {\n");
            for (k = 0; k < 4; k++) {
                fprintf(out, "   {");
                write_table(out, ltl[k], 256);
                fprintf(out, "}%s", k < 3 ? ",\n" : "");
            }
            fprintf(out,
            "};\n"
            "\n"
            "static const word_t crc_braid_big_table[][256] = {\n");
            for (k = 0; k < 4; k++) {
                fprintf(out, "   {");
                write_table32hi(out, big[k], 256);
                fprintf(out, "}%s", k < 3 ? ",\n" : "");
            }
            fprintf(out,
            "};\n"
            "\n"
            "#endif\n"
            "\n"
            "#endif\n");
        }
        fprintf(out,
            "\n"
            "#endif\n");

        /* write out zeros operator table to crc32.h */
        fprintf(out,
            "\n"
            "static const crc_t x2n_table[] = {\n"
            "    ");
        write_table(out, x2n_table, 32);
        fprintf(out,
            "};\n");
        fclose(out);
    }
#endif /* MAKECRCH */
}

#ifdef MAKECRCH

/*
   Write the 32-bit values in table[0..k-1] to out, five per line in
   hexadecimal separated by commas.
 */
static void write_table(FILE *out, const crc_t *table, int k) {
    int n;

    for (n = 0; n < k; n++)
        fprintf(out, "%s0x%08lx%s", n == 0 || n % 5 ? "" : "    ",
                (unsigned long)(table[n]),
                n == k - 1 ? "" : (n % 5 == 4 ? ",\n" : ", "));
}

/*
   Write the high 32-bits of each value in table[0..k-1] to out, five per line
   in hexadecimal separated by commas.
 */
static void write_table32hi(FILE *out, const word_t *table, int k) {
    int n;

    for (n = 0; n < k; n++)
        fprintf(out, "%s0x%08lx%s", n == 0 || n % 5 ? "" : "    ",
                (unsigned long)(table[n] >> 32),
                n == k - 1 ? "" : (n % 5 == 4 ? ",\n" : ", "));
}

/*
  Write the 64-bit values in table[0..k-1] to out, three per line in
  hexadecimal separated by commas. This assumes that if there is a 64-bit
  type, then there is also a long long integer type, and it is at least 64
  bits. If not, then the type cast and format string can be adjusted
  accordingly.
 */
static void write_table64(FILE *out, const word_t *table, int k) {
    int n;

    for (n = 0; n < k; n++)
        fprintf(out, "%s0x%016llx%s", n == 0 || n % 3 ? "" : "    ",
                (unsigned long long)(table[n]),
                n == k - 1 ? "" : (n % 3 == 2 ? ",\n" : ", "));
}

/* Actually do the deed. */
int main(void) {
    make_crc_table();
    return 0;
}

#endif /* MAKECRCH */

#ifdef W
/*
  Generate the little and big-endian braid tables for the given n and word_t
  size w. Each array must have room for w blocks of 256 elements.
 */
static void braid(crc_t ltl[][256], word_t big[][256], int n, int w) {
    int k;
    crc_t i, p, q;
    for (k = 0; k < w; k++) {
        p = x2nmodp((n * w + 3 - k) << 3, 0);
        ltl[k][0] = 0;
        big[w - 1 - k][0] = 0;
        for (i = 1; i < 256; i++) {
            ltl[k][i] = q = multmodp(i << 24, p);
            big[w - 1 - k][i] = byte_swap(q);
        }
    }
}
#endif

#endif /* DYNAMIC_CRC_TABLE */

/* =========================================================================
 * Use ARM machine instructions if available. This will compute the CRC about
 * ten times faster than the braided calculation. This code does not check for
 * the presence of the CRC instruction at run time. __ARM_FEATURE_CRC32 will
 * only be defined if the compilation specifies an ARM processor architecture
 * that has the instructions. For example, compiling with -march=armv8.1-a or
 * -march=armv8-a+crc, or -march=native if the compile machine has the crc32
 * instructions.
 */
#ifdef ARMCRC32

/*
  Return a(x) multiplied by b(x) modulo p(x), where p(x) is the CRC polynomial,
  reflected. For speed, this requires that a not be zero.
 */
static crc_t multmodp(crc_t a, crc_t b) {
    crc_t m, p;

    m = (crc_t)1 << 31;
    p = 0;
    for (;;) {
        if (a & m) {
            p ^= b;
            if ((a & (m - 1)) == 0)
                break;
        }
        m >>= 1;
        b = b & 1 ? (b >> 1) ^ POLY : b >> 1;
    }
    return p;
}

/*
  Return x^(n * 2^k) modulo p(x). Requires that x2n_table[] has been
  initialized.
 */
static crc_t x2nmodp(off64_t n, unsigned k) {
    crc_t p;

    p = (crc_t)1 << 31;           /* x^0 == 1 */
    while (n) {
        if (n & 1)
            p = multmodp(x2n_table[k & 31], p);
        n >>= 1;
        k++;
    }
    return p;
}

/*
   Constants empirically determined to maximize speed. These values are from
   measurements on a Cortex-A57. Your mileage may vary.
 */
#define Z_BATCH 3990                /* number of words in a batch */
#define Z_BATCH_ZEROS 0xa10d3d0c    /* computed from Z_BATCH = 3990 */
#define Z_BATCH_MIN 800             /* fewest words in a final batch */

uint32_t cdrom_crc32(unsigned long crc, const unsigned char *buf,
                     size_t len) {
    crc_t val;
    word_t crc1, crc2;
    const word_t *word;
    word_t val0, val1, val2;
    size_t last, last2, i;
    size_t num;

    /* Return initial CRC, if requested. */
    if (buf == NULL)
        return 0;

#ifdef DYNAMIC_CRC_TABLE
    once(&made, make_crc_table);
#endif /* DYNAMIC_CRC_TABLE */

    /* Pre-condition the CRC */
    crc = (~crc) & 0xffffffff;

    /* Compute the CRC up to a word boundary. */
    while (len && ((size_t) buf & 7) != 0) {
        len--;
        val = *buf++;
        __asm__ volatile("crc32b %w0, %w0, %w1" : "+r"(crc) : "r"(val));
    }

    /* Prepare to compute the CRC on full 64-bit words word[0..num-1]. */
    word = (word_t const *)buf;
    num = len >> 3;
    len &= 7;

    /* Do three interleaved CRCs to realize the throughput of one crc32x
       instruction per cycle. Each CRC is calculated on Z_BATCH words. The
       three CRCs are combined into a single CRC after each set of batches. */
    while (num >= 3 * Z_BATCH) {
        crc1 = 0;
        crc2 = 0;
        for (i = 0; i < Z_BATCH; i++) {
            val0 = word[i];
            val1 = word[i + Z_BATCH];
            val2 = word[i + 2 * Z_BATCH];
            __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc) : "r"(val0));
            __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc1) : "r"(val1));
            __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc2) : "r"(val2));
        }
        word += 3 * Z_BATCH;
        num -= 3 * Z_BATCH;
        crc = multmodp(Z_BATCH_ZEROS, crc) ^ crc1;
        crc = multmodp(Z_BATCH_ZEROS, crc) ^ crc2;
    }

    /* Do one last smaller batch with the remaining words, if there are enough
       to pay for the combination of CRCs. */
    last = num / 3;
    if (last >= Z_BATCH_MIN) {
        last2 = last << 1;
        crc1 = 0;
        crc2 = 0;
        for (i = 0; i < last; i++) {
            val0 = word[i];
            val1 = word[i + last];
            val2 = word[i + last2];
            __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc) : "r"(val0));
            __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc1) : "r"(val1));
            __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc2) : "r"(val2));
        }
        word += 3 * last;
        num -= 3 * last;
        val = x2nmodp(last, 6);
        crc = multmodp(val, crc) ^ crc1;
        crc = multmodp(val, crc) ^ crc2;
    }

    /* Compute the CRC on any remaining words. */
    for (i = 0; i < num; i++) {
        val0 = word[i];
        __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc) : "r"(val0));
    }
    word += num;

    /* Complete the CRC on any remaining bytes. */
    buf = (const unsigned char *) word;
    while (len) {
        len--;
        val = *buf++;
        __asm__ volatile("crc32b %w0, %w0, %w1" : "+r"(crc) : "r"(val));
    }

    /* Return the CRC, post-conditioned. */
    return crc ^ 0xffffffff;
}

#else

#ifdef W

/*
  Return the CRC of the W bytes in the word_t data, taking the
  least-significant byte of the word as the first byte of data, without any pre
  or post conditioning. This is used to combine the CRCs of each braid.
 */
static crc_t crc_word(word_t data) {
    int k;
    for (k = 0; k < W; k++)
        data = (data >> 8) ^ crc_table[data & 0xff];
    return (crc_t) data;
}

static word_t crc_word_big(word_t data) {
    int k;
    for (k = 0; k < W; k++)
        data = (data << 8) ^
            crc_big_table[(data >> ((W - 1) << 3)) & 0xff];
    return data;
}

#endif

/* ========================================================================= */
unsigned long cdrom_crc32(unsigned long crc, const unsigned char *buf,
                          size_t len) {
    /* Return initial CRC, if requested. */
    if (buf == NULL)
        return 0;

#ifdef DYNAMIC_CRC_TABLE
    once(&made, make_crc_table);
#endif /* DYNAMIC_CRC_TABLE */

    /* Pre-condition the CRC */
    crc = (~crc) & 0xffffffff;

#ifdef W

    /* If provided enough bytes, do a braided CRC calculation. */
    if (len >= N * W + W - 1) {
        size_t blks;
        word_t const *words;
        unsigned endian;
        int k;

        /* Compute the CRC up to a word_t boundary. */
        while (len && ((size_t) buf & (W - 1)) != 0) {
            len--;
            crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
        }

        /* Compute the CRC on as many N word_t blocks as are available. */
        blks = len / (N * W);
        len -= blks * N * W;
        words = (word_t const *)buf;

        /* Do endian check at execution time instead of compile time, since ARM
           processors can change the endianness at execution time. If the
           compiler knows what the endianness will be, it can optimize out the
           check and the unused branch. */
        endian = 1;
        if (*(unsigned char *)&endian) {
            /* Little endian. */

            crc_t crc0;
            word_t word0;
#if N > 1
            crc_t crc1;
            word_t word1;
#if N > 2
            crc_t crc2;
            word_t word2;
#if N > 3
            crc_t crc3;
            word_t word3;
#if N > 4
            crc_t crc4;
            word_t word4;
#if N > 5
            crc_t crc5;
            word_t word5;
#endif
#endif
#endif
#endif
#endif

            /* Initialize the CRC for each braid. */
            crc0 = crc;
#if N > 1
            crc1 = 0;
#if N > 2
            crc2 = 0;
#if N > 3
            crc3 = 0;
#if N > 4
            crc4 = 0;
#if N > 5
            crc5 = 0;
#endif
#endif
#endif
#endif
#endif

            /*
              Process the first blks-1 blocks, computing the CRCs on each braid
              independently.
             */
            while (--blks) {
                /* Load the word for each braid into registers. */
                word0 = crc0 ^ words[0];
#if N > 1
                word1 = crc1 ^ words[1];
#if N > 2
                word2 = crc2 ^ words[2];
#if N > 3
                word3 = crc3 ^ words[3];
#if N > 4
                word4 = crc4 ^ words[4];
#if N > 5
                word5 = crc5 ^ words[5];
#endif
#endif
#endif
#endif
#endif
                words += N;

                /* Compute and update the CRC for each word. The loop should
                   get unrolled. */
                crc0 = crc_braid_table[0][word0 & 0xff];
#if N > 1
                crc1 = crc_braid_table[0][word1 & 0xff];
#if N > 2
                crc2 = crc_braid_table[0][word2 & 0xff];
#if N > 3
                crc3 = crc_braid_table[0][word3 & 0xff];
#if N > 4
                crc4 = crc_braid_table[0][word4 & 0xff];
#if N > 5
                crc5 = crc_braid_table[0][word5 & 0xff];
#endif
#endif
#endif
#endif
#endif
                for (k = 1; k < W; k++) {
                    crc0 ^= crc_braid_table[k][(word0 >> (k << 3)) & 0xff];
#if N > 1
                    crc1 ^= crc_braid_table[k][(word1 >> (k << 3)) & 0xff];
#if N > 2
                    crc2 ^= crc_braid_table[k][(word2 >> (k << 3)) & 0xff];
#if N > 3
                    crc3 ^= crc_braid_table[k][(word3 >> (k << 3)) & 0xff];
#if N > 4
                    crc4 ^= crc_braid_table[k][(word4 >> (k << 3)) & 0xff];
#if N > 5
                    crc5 ^= crc_braid_table[k][(word5 >> (k << 3)) & 0xff];
#endif
#endif
#endif
#endif
#endif
                }
            }

            /*
              Process the last block, combining the CRCs of the N braids at the
              same time.
             */
            crc = crc_word(crc0 ^ words[0]);
#if N > 1
            crc = crc_word(crc1 ^ words[1] ^ crc);
#if N > 2
            crc = crc_word(crc2 ^ words[2] ^ crc);
#if N > 3
            crc = crc_word(crc3 ^ words[3] ^ crc);
#if N > 4
            crc = crc_word(crc4 ^ words[4] ^ crc);
#if N > 5
            crc = crc_word(crc5 ^ words[5] ^ crc);
#endif
#endif
#endif
#endif
#endif
            words += N;
        }
        else {
            /* Big endian. */

            word_t crc0, word0, comb;
#if N > 1
            word_t crc1, word1;
#if N > 2
            word_t crc2, word2;
#if N > 3
            word_t crc3, word3;
#if N > 4
            word_t crc4, word4;
#if N > 5
            word_t crc5, word5;
#endif
#endif
#endif
#endif
#endif

            /* Initialize the CRC for each braid. */
            crc0 = byte_swap(crc);
#if N > 1
            crc1 = 0;
#if N > 2
            crc2 = 0;
#if N > 3
            crc3 = 0;
#if N > 4
            crc4 = 0;
#if N > 5
            crc5 = 0;
#endif
#endif
#endif
#endif
#endif

            /*
              Process the first blks-1 blocks, computing the CRCs on each braid
              independently.
             */
            while (--blks) {
                /* Load the word for each braid into registers. */
                word0 = crc0 ^ words[0];
#if N > 1
                word1 = crc1 ^ words[1];
#if N > 2
                word2 = crc2 ^ words[2];
#if N > 3
                word3 = crc3 ^ words[3];
#if N > 4
                word4 = crc4 ^ words[4];
#if N > 5
                word5 = crc5 ^ words[5];
#endif
#endif
#endif
#endif
#endif
                words += N;

                /* Compute and update the CRC for each word. The loop should
                   get unrolled. */
                crc0 = crc_braid_big_table[0][word0 & 0xff];
#if N > 1
                crc1 = crc_braid_big_table[0][word1 & 0xff];
#if N > 2
                crc2 = crc_braid_big_table[0][word2 & 0xff];
#if N > 3
                crc3 = crc_braid_big_table[0][word3 & 0xff];
#if N > 4
                crc4 = crc_braid_big_table[0][word4 & 0xff];
#if N > 5
                crc5 = crc_braid_big_table[0][word5 & 0xff];
#endif
#endif
#endif
#endif
#endif
                for (k = 1; k < W; k++) {
                    crc0 ^= crc_braid_big_table[k][(word0 >> (k << 3)) & 0xff];
#if N > 1
                    crc1 ^= crc_braid_big_table[k][(word1 >> (k << 3)) & 0xff];
#if N > 2
                    crc2 ^= crc_braid_big_table[k][(word2 >> (k << 3)) & 0xff];
#if N > 3
                    crc3 ^= crc_braid_big_table[k][(word3 >> (k << 3)) & 0xff];
#if N > 4
                    crc4 ^= crc_braid_big_table[k][(word4 >> (k << 3)) & 0xff];
#if N > 5
                    crc5 ^= crc_braid_big_table[k][(word5 >> (k << 3)) & 0xff];
#endif
#endif
#endif
#endif
#endif
                }
            }

            /*
              Process the last block, combining the CRCs of the N braids at the
              same time.
             */
            comb = crc_word_big(crc0 ^ words[0]);
#if N > 1
            comb = crc_word_big(crc1 ^ words[1] ^ comb);
#if N > 2
            comb = crc_word_big(crc2 ^ words[2] ^ comb);
#if N > 3
            comb = crc_word_big(crc3 ^ words[3] ^ comb);
#if N > 4
            comb = crc_word_big(crc4 ^ words[4] ^ comb);
#if N > 5
            comb = crc_word_big(crc5 ^ words[5] ^ comb);
#endif
#endif
#endif
#endif
#endif
            words += N;
            crc = byte_swap(comb);
        }

        /*
          Update the pointer to the remaining bytes to process.
         */
        buf = (unsigned char const *)words;
    }

#endif /* W */

    /* Complete the computation of the CRC on any remaining bytes. */
    while (len >= 8) {
        len -= 8;
        crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
        crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
        crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
        crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
        crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
        crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
        crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
        crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
    }
    while (len) {
        len--;
        crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
    }

    /* Return the CRC, post-conditioned. */
    return crc ^ 0xffffffff;
}

#endif
