adler32_p.h

/* adler32_p.h -- Private inline functions and macros shared with
 *                different computation of 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
 */

#ifndef ADLER32_P_H
#define ADLER32_P_H

#define BASE 65521U     /* largest prime smaller than 65536 */
#define NMAX 5552
/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
#define NMAX_ALIGNED32 (NMAX & ~31)
/* NMAX rounded down to a multiple of 32 is 5536 */

#define ADLER_DO1(sum1, sum2, buf, i)  {(sum1) += buf[(i)]; (sum2) += (sum1);}
#define ADLER_DO2(sum1, sum2, buf, i)  {ADLER_DO1(sum1, sum2, buf, i); ADLER_DO1(sum1, sum2, buf, i+1);}
#define ADLER_DO4(sum1, sum2, buf, i)  {ADLER_DO2(sum1, sum2, buf, i); ADLER_DO2(sum1, sum2, buf, i+2);}
#define ADLER_DO8(sum1, sum2, buf, i)  {ADLER_DO4(sum1, sum2, buf, i); ADLER_DO4(sum1, sum2, buf, i+4);}
#define ADLER_DO16(sum1, sum2, buf)    {ADLER_DO8(sum1, sum2, buf, 0); ADLER_DO8(sum1, sum2, buf, 8);}

Z_FORCEINLINE static void adler32_copy_align(uint32_t *Z_RESTRICT adler, uint8_t *dst, const uint8_t *buf, size_t len,
                                             uint32_t *Z_RESTRICT sum2, const int MAX_LEN, const int COPY) {
    Z_UNUSED(MAX_LEN);
    if (len & 1) {
        if (COPY) {
            *dst = *buf;
            dst += 1;
        }
        ADLER_DO1(*adler, *sum2, buf, 0);
        buf += 1;
    }
    if (len & 2) {
        if (COPY) {
            memcpy(dst, buf, 2);
            dst += 2;
        }
        ADLER_DO2(*adler, *sum2, buf, 0);
        buf += 2;
    }
    while (len >= 4) {
        if (COPY) {
            memcpy(dst, buf, 4);
            dst += 4;
        }
        len -= 4;
        ADLER_DO4(*adler, *sum2, buf, 0);
        buf += 4;
    }
}

Z_FORCEINLINE static uint32_t adler32_copy_tail(uint32_t adler, uint8_t *dst, const uint8_t *buf, size_t len,
                                                uint32_t sum2, const int REBASE, const int MAX_LEN, const int COPY) {
    if (len) {
        /* DO16 loop for large remainders only (scalar, risc-v). */
        if (MAX_LEN >= 32) {
            while (len >= 16) {
                if (COPY) {
                    memcpy(dst, buf, 16);
                    dst += 16;
                }
                len -= 16;
                ADLER_DO16(adler, sum2, buf);
                buf += 16;
            }
        }
        /* DO4 loop avoids GCC x86 register pressure from hoisted DO8/DO16 loads. */
        while (len >= 4) {
            if (COPY) {
                memcpy(dst, buf, 4);
                dst += 4;
            }
            len -= 4;
            ADLER_DO4(adler, sum2, buf, 0);
            buf += 4;
        }
        if (len & 2) {
            if (COPY) {
                memcpy(dst, buf, 2);
                dst += 2;
            }
            ADLER_DO2(adler, sum2, buf, 0);
            buf += 2;
        }
        if (len & 1) {
            if (COPY)
                *dst = *buf;
            ADLER_DO1(adler, sum2, buf, 0);
        }
    }
    if (REBASE) {
        adler %= BASE;
        sum2 %= BASE;
    }
    /* D = B * 65536 + A, see: https://en.wikipedia.org/wiki/Adler-32. */
    return adler | (sum2 << 16);
}

#endif /* ADLER32_P_H */