Aaru.Checksums.Native/fletcher16.c

/*
 * This file is part of the Aaru Data Preservation Suite.
 * Copyright (c) 2019-2021 Natalia Portillo.
 */

/* adler32.c -- compute the Adler-32 checksum of a data stream
  Copyright (C) 1995-2011 Mark Adler

 This software is provided 'as-is', without any express or implied
 warranty.  In no event will the authors be held liable for any damages
 arising from the use of this software.
 Permission is granted to anyone to use this software for any purpose,
 including commercial applications, and to alter it and redistribute it
 freely, subject to the following restrictions:
 1. The origin of this software must not be misrepresented; you must not
    claim that you wrote the original software. If you use this software
    in a product, an acknowledgment in the product documentation would be
    appreciated but is not required.
 2. Altered source versions must be plainly marked as such, and must not be
    misrepresented as being the original software.
 3. This notice may not be removed or altered from any source distribution.

 Jean-loup Gailly        Mark Adler
 jloup@gzip.org          madler@alumni.caltech.edu
*/

#include <stdint.h>
#include <stdlib.h>

#include "library.h"
#include "fletcher16.h"

AARU_EXPORT fletcher16_ctx* AARU_CALL fletcher16_init()
{
    fletcher16_ctx* ctx;

    ctx = (fletcher16_ctx*)malloc(sizeof(fletcher16_ctx));

    if(!ctx) return NULL;

    ctx->sum1 = 0xFF;
    ctx->sum2 = 0xFF;

    return ctx;
}

AARU_EXPORT int AARU_CALL fletcher16_update(fletcher16_ctx* ctx, const uint8_t* data, uint32_t len)
{
    if(!ctx || !data) return -1;

    uint32_t sum1 = ctx->sum1;
    uint32_t sum2 = ctx->sum2;
    unsigned n;

    /* in case user likes doing a byte at a time, keep it fast */
    if(len == 1)
    {
        sum1 += data[0];
        if(sum1 >= FLETCHER16_MODULE) sum1 -= FLETCHER16_MODULE;
        sum2 += sum1;
        if(sum2 >= FLETCHER16_MODULE) sum2 -= FLETCHER16_MODULE;

        ctx->sum1 = sum1 & 0xFF;
        ctx->sum2 = sum2 & 0xFF;
        return 0;
    }

    /* in case short lengths are provided, keep it somewhat fast */
    if(len < 11)
    {
        while(len--)
        {
            sum1 += *data++;
            sum2 += sum1;
        }
        if(sum1 >= FLETCHER16_MODULE) sum1 -= FLETCHER16_MODULE;
        sum2 %= FLETCHER16_MODULE; /* only added so many FLETCHER16_MODULE's */
        ctx->sum1 = sum1 & 0xFF;
        ctx->sum2 = sum2 & 0xFF;
        return 0;
    }

    /* do length NMAX blocks -- requires just one modulo operation */
    while(len >= NMAX)
    {
        len -= NMAX;
        n = NMAX / 11; /* NMAX is divisible by 11 */
        do {
            sum1 += (data)[0];
            sum2 += sum1;
            sum1 += (data)[0 + 1];
            sum2 += sum1;
            sum1 += (data)[0 + 2];
            sum2 += sum1;
            sum1 += (data)[0 + 2 + 1];
            sum2 += sum1;
            sum1 += (data)[0 + 4];
            sum2 += sum1;
            sum1 += (data)[0 + 4 + 1];
            sum2 += sum1;
            sum1 += (data)[0 + 4 + 2];
            sum2 += sum1;
            sum1 += (data)[0 + 4 + 2 + 1];
            sum2 += sum1;
            sum1 += (data)[8];
            sum2 += sum1;
            sum1 += (data)[8 + 1];
            sum2 += sum1;
            sum1 += (data)[8 + 2];
            sum2 += sum1;

            /* 11 sums unrolled */
            data += 11;
        } while(--n);
        sum1 %= FLETCHER16_MODULE;
        sum2 %= FLETCHER16_MODULE;
    }

    /* do remaining bytes (less than NMAX, still just one modulo) */
    if(len)
    { /* avoid modulos if none remaining */
        while(len >= 11)
        {
            len -= 11;
            sum1 += (data)[0];
            sum2 += sum1;
            sum1 += (data)[0 + 1];
            sum2 += sum1;
            sum1 += (data)[0 + 2];
            sum2 += sum1;
            sum1 += (data)[0 + 2 + 1];
            sum2 += sum1;
            sum1 += (data)[0 + 4];
            sum2 += sum1;
            sum1 += (data)[0 + 4 + 1];
            sum2 += sum1;
            sum1 += (data)[0 + 4 + 2];
            sum2 += sum1;
            sum1 += (data)[0 + 4 + 2 + 1];
            sum2 += sum1;
            sum1 += (data)[8];
            sum2 += sum1;
            sum1 += (data)[8 + 1];
            sum2 += sum1;
            sum1 += (data)[8 + 2];
            sum2 += sum1;

            data += 11;
        }
        while(len--)
        {
            sum1 += *data++;
            sum2 += sum1;
        }
        sum1 %= FLETCHER16_MODULE;
        sum2 %= FLETCHER16_MODULE;
    }

    ctx->sum1 = sum1 & 0xFF;
    ctx->sum2 = sum2 & 0xFF;
    return 0;
}

AARU_EXPORT int AARU_CALL fletcher16_final(fletcher16_ctx* ctx, uint16_t* checksum)
{
    if(!ctx) return -1;

    *checksum = (ctx->sum2 << 8) | ctx->sum1;
    return 0;
}

AARU_EXPORT void AARU_CALL fletcher16_free(fletcher16_ctx* ctx)
{
    if(!ctx) return;

    free(ctx);
}