library/gf128mul.c

/*
 *  GF(2^128) multiplication functions
 *
 *  Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
 *  SPDX-License-Identifier: Apache-2.0
 *
 *  Licensed under the Apache License, Version 2.0 (the "License"); you may
 *  not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 *  This file is part of mbed TLS (https://tls.mbed.org)
 */
#include <stdint.h>

#include "mbedtls/gf128mul.h"

/* Endianess with 64 bits values */
#ifndef GET_UINT64_LE
#define GET_UINT64_LE(n,b,i)                            \
{                                                       \
    (n) = ( (uint64_t) (b)[(i) + 7] << 56 )             \
        | ( (uint64_t) (b)[(i) + 6] << 48 )             \
        | ( (uint64_t) (b)[(i) + 5] << 40 )             \
        | ( (uint64_t) (b)[(i) + 4] << 32 )             \
        | ( (uint64_t) (b)[(i) + 3] << 24 )             \
        | ( (uint64_t) (b)[(i) + 2] << 16 )             \
        | ( (uint64_t) (b)[(i) + 1] <<  8 )             \
        | ( (uint64_t) (b)[(i)    ]       );            \
}
#endif

#ifndef PUT_UINT64_LE
#define PUT_UINT64_LE(n,b,i)                            \
{                                                       \
    (b)[(i) + 7] = (unsigned char) ( (n) >> 56 );       \
    (b)[(i) + 6] = (unsigned char) ( (n) >> 48 );       \
    (b)[(i) + 5] = (unsigned char) ( (n) >> 40 );       \
    (b)[(i) + 4] = (unsigned char) ( (n) >> 32 );       \
    (b)[(i) + 3] = (unsigned char) ( (n) >> 24 );       \
    (b)[(i) + 2] = (unsigned char) ( (n) >> 16 );       \
    (b)[(i) + 1] = (unsigned char) ( (n) >>  8 );       \
    (b)[(i)    ] = (unsigned char) ( (n)       );       \
}
#endif


/* Jump table for not having ifs */
static const uint16_t gf128mul_table_bbe[2] = { 0x00, 0x87 };


/*
 * This function multiply a field element by x, by x^4 and by x^8
 * in the polynomial field representation. It uses 64-bit word operations
 * to gain speed but compensates for machine endianess and hence works
 * correctly on both styles of machine.
 */
void mbedtls_gf128mul_x_ble(mbedtls_be128 r, const mbedtls_be128 x)
{
    uint64_t a, b, ra, rb;

    GET_UINT64_LE(a, x, 0);
    GET_UINT64_LE(b, x, 8);

    ra = (a << 1)  ^ gf128mul_table_bbe[b >> 63];
    rb = (a >> 63) | (b << 1);

    PUT_UINT64_LE(ra, r, 0);
    PUT_UINT64_LE(rb, r, 8);
}