/* adler32.c -- compute the Adler-32 checksum of a data stream

 * Copyright (C) 1995-2011, 2016 Mark Adler

 * For conditions of distribution and use, see copyright notice in zlib.h

 */

#include "zbuild.h"

#include "zutil.h"

#include "functable.h"

#include "adler32_p.h"

/* ========================================================================= */

Z_INTERNAL uint32_t adler32_c(uint32_t adler, const unsigned char *buf, size_t len) {

    uint32_t sum2;

    unsigned n;

    /* split Adler-32 into component sums */

    sum2 = (adler >> 16) & 0xffff;

    adler &= 0xffff;

    /* in case user likes doing a byte at a time, keep it fast */

    if (UNLIKELY(len == 1))

        return adler32_len_1(adler, buf, sum2);

    /* initial Adler-32 value (deferred check for len == 1 speed) */

    if (UNLIKELY(buf == NULL))

        return 1L;

    /* in case short lengths are provided, keep it somewhat fast */

    if (UNLIKELY(len < 16))

        return adler32_len_16(adler, buf, len, sum2);

    /* do length NMAX blocks -- requires just one modulo operation */

    while (len >= NMAX) {

        len -= NMAX;

#ifdef UNROLL_MORE

        n = NMAX / 16;          /* NMAX is divisible by 16 */

#else

        n = NMAX / 8;           /* NMAX is divisible by 8 */

#endif

        do {

#ifdef UNROLL_MORE

            DO16(adler, sum2, buf);          /* 16 sums unrolled */

            buf += 16;

#else

            DO8(adler, sum2, buf, 0);         /* 8 sums unrolled */

            buf += 8;

#endif

        } while (--n);

        adler %= BASE;

        sum2 %= BASE;

    }

    /* do remaining bytes (less than NMAX, still just one modulo) */

    if (len) {                  /* avoid modulos if none remaining */

#ifdef UNROLL_MORE

        while (len >= 16) {

            len -= 16;

            DO16(adler, sum2, buf);

            buf += 16;

#else

        while (len >= 8) {

            len -= 8;

            DO8(adler, sum2, buf, 0);

            buf += 8;

#endif

        }

        while (len) {

            --len;

            adler += *buf++;

            sum2 += adler;

        }

        adler %= BASE;

        sum2 %= BASE;

    }

    /* return recombined sums */

    return adler | (sum2 << 16);

}

#ifdef ZLIB_COMPAT

unsigned long Z_EXPORT PREFIX(adler32_z)(unsigned long adler, const unsigned char *buf, size_t len) {

    return (unsigned long)functable.adler32((uint32_t)adler, buf, len);

}

#else

uint32_t Z_EXPORT PREFIX(adler32_z)(uint32_t adler, const unsigned char *buf, size_t len) {

    return functable.adler32(adler, buf, len);

}

#endif

/* ========================================================================= */

#ifdef ZLIB_COMPAT

unsigned long Z_EXPORT PREFIX(adler32)(unsigned long adler, const unsigned char *buf, unsigned int len) {

    return (unsigned long)functable.adler32((uint32_t)adler, buf, len);

}

#else

uint32_t Z_EXPORT PREFIX(adler32)(uint32_t adler, const unsigned char *buf, uint32_t len) {

    return functable.adler32(adler, buf, len);

}

#endif

/* ========================================================================= */

static uint32_t adler32_combine_(uint32_t adler1, uint32_t adler2, z_off64_t len2) {

    uint32_t sum1;

    uint32_t sum2;

    unsigned rem;

    /* for negative len, return invalid adler32 as a clue for debugging */

    if (len2 < 0)

        return 0xffffffff;

    /* the derivation of this formula is left as an exercise for the reader */

    len2 %= BASE;                 /* assumes len2 >= 0 */

    rem = (unsigned)len2;

    sum1 = adler1 & 0xffff;

    sum2 = rem * sum1;

    sum2 %= BASE;

    sum1 += (adler2 & 0xffff) + BASE - 1;

    sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;

    if (sum1 >= BASE) sum1 -= BASE;

    if (sum1 >= BASE) sum1 -= BASE;

    if (sum2 >= ((unsigned long)BASE << 1)) sum2 -= ((unsigned long)BASE << 1);

    if (sum2 >= BASE) sum2 -= BASE;

    return sum1 | (sum2 << 16);

}

/* ========================================================================= */

#ifdef ZLIB_COMPAT

unsigned long Z_EXPORT PREFIX(adler32_combine)(unsigned long adler1, unsigned long adler2, z_off_t len2) {

    return (unsigned long)adler32_combine_((uint32_t)adler1, (uint32_t)adler2, len2);

}

unsigned long Z_EXPORT PREFIX4(adler32_combine)(unsigned long adler1, unsigned long adler2, z_off64_t len2) {

    return (unsigned long)adler32_combine_((uint32_t)adler1, (uint32_t)adler2, len2);

}

#else

uint32_t Z_EXPORT PREFIX4(adler32_combine)(uint32_t adler1, uint32_t adler2, z_off64_t len2) {

    return adler32_combine_(adler1, adler2, len2);

}

#endif