/* $Id$ */
/*
 * Copyright (C) 1998-2002 RSA Security Inc. All rights reserved.
 *
 * This work contains proprietary information of RSA Security.
 * Distribution is limited to authorized licensees of RSA
 * Security. Any unauthorized reproduction, distribution or
 * modification of this work is strictly prohibited.
 *
 */

#include "bn_lcl.h"

int BN_MONT_CTX_set_word(mont,mod,ctx)
BN_MONT_CTX *mont;
BIGNUM *mod;
BN_CTX *ctx;
    {
    BIGNUM Ri,*R;
#if 1
    BN_ULONG tmod,rr;
#else
    BN_ULONG buf[2];
    BIGNUM tmod;
#endif


    bn_check_top(mod);
    if (mod->top == 0) return(0);

    R= &(mont->RR);                 /* grab RR as a temp */
    if (BN_copy(&(mont->N),mod) == NULL)        /* Set N */
        return(0);

    BN_init(&Ri);

    mont->use_word=1;

/* EAY is this number of words to shift, or the number to shift to end up
 * with a '1' in the next word?
 * for 8 bit words, is 0x01ab == 1 or 2
 */
    mont->riw=(BN_num_bits(mod)+(BN_BITS2-1))/BN_BITS2;
    if (!BN_zero(R)) return(0);

        /* We are now setting a number which is larger than our current 
     * one after we do the shift 
     */
    if (!BN_set_bit(R,BN_BITS2))
        goto err;

#if 0
    tmod.d=buf;
    tmod.top=1;
    tmod.max=mod->max;
    tmod.neg=mod->neg;
    buf[0]=mod->d[0]&BN_MASK2;
    buf[1]=0;

    if ((BN_mod_inverse(&Ri,R,&tmod,ctx)) == NULL)
        goto err;
#else
    tmod=mod->d[0];
    rr=BN_mod_inverse_word(tmod);
    if (!BN_set_word(&Ri,rr))
        goto err;
#endif

    /* R*Ri */
    if (!BN_lshift(&Ri,&Ri,BN_BITS2))
        goto err;

    if (!BN_is_zero(&Ri))
        (void)BN_sub_word(&Ri,1);
    else
        {
        /* This is not common..., 1 in BN_MASK2,
         * It happens when buf[0] was == 1.  So for 8 bit,
         * this is 1/256, 16bit, 1 in 2^16 etc.
         */
        if (!BN_set_word(&Ri,BN_MASK2))
            goto err;
        }
#if 0
    BN_div(&Ri,NULL,&Ri,&tmod,ctx);
    //BN_div_word(&Ri,tmod);
    mont->n0=Ri.d[0];
#else
#if 0
    {
    BN_ULONG h,l;

    h=l=0;
    if (Ri.top >= 2) h=Ri.d[1];
    if (Ri.top >= 1) l=Ri.d[0];
    mont->n0=bn_div_words(h,l,tmod);
    }
#endif
    mont->n0=bn_div_words(
        (Ri.top >= 2)?Ri.d[1]:0,
        (Ri.top >= 1)?Ri.d[0]:0,
        tmod);
#endif
    /* mod->top=z; */

    /* setup RR for conversions */
    (void)BN_zero(&(mont->RR));
    if (!BN_set_bit(&(mont->RR),mont->riw*2*BN_BITS2))
        goto err;
    (void)BN_mod(&(mont->RR),&(mont->RR),&(mont->N),ctx);
    bn_zexpand(&(mont->RR),mont->riw);
#if 0
    bn_zexpand(&(mont->Ni),mont->riw); /*This is not used? */
#endif

err:
    BN_free(&Ri);
    return(1);
    }