openssl/crypto/ec/curve448/arch_32/f_impl.h

/*
 * Copyright 2017-2018 The OpenSSL Project Authors. All Rights Reserved.
 * Copyright 2014-2016 Cryptography Research, Inc.
 *
 * Licensed under the OpenSSL license (the "License").  You may not use
 * this file except in compliance with the License.  You can obtain a copy
 * in the file LICENSE in the source distribution or at
 * https://www.openssl.org/source/license.html
 *
 * Originally written by Mike Hamburg
 */
#define GF_HEADROOM 2
#define LIMB(x) (x)&((1<<28)-1), (x)>>28
#define FIELD_LITERAL(a,b,c,d,e,f,g,h) \
    {{LIMB(a),LIMB(b),LIMB(c),LIMB(d),LIMB(e),LIMB(f),LIMB(g),LIMB(h)}}

#define LIMB_PLACE_VALUE(i) 28

void gf_add_RAW(gf out, const gf a, const gf b)
{
    unsigned int i;

    for (i = 0; i < NLIMBS; i++) {
        out->limb[i] = a->limb[i] + b->limb[i];
    }
}

void gf_sub_RAW(gf out, const gf a, const gf b)
{
    unsigned int i;

    for (i = 0; i < sizeof(*out) / sizeof(out->limb[0]); i++) {
        out->limb[i] = a->limb[i] - b->limb[i];
    }
}

void gf_bias(gf a, int amt)
{
    unsigned int i;
    uint32_t co1 = ((1 << 28) - 1) * amt, co2 = co1 - amt;

    for (i = 0; i < sizeof(*a) / sizeof(a->limb[0]); i++)
        a->limb[i] += (i == sizeof(*a) / sizeof(a->limb[0]) / 2) ? co2 : co1;
}

void gf_weak_reduce(gf a)
{
    uint32_t mask = (1 << 28) - 1;
    uint32_t tmp = a->limb[15] >> 28;
    unsigned int i;

    a->limb[8] += tmp;
    for (i = 15; i > 0; i--)
        a->limb[i] = (a->limb[i] & mask) + (a->limb[i - 1] >> 28);
    a->limb[0] = (a->limb[0] & mask) + tmp;
}