/* $Id$ */
/*
 * 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"

void BN_RECP_CTX_init(recp)
BN_RECP_CTX *recp;
    {
    BN_init(&(recp->N));
    BN_init(&(recp->Nr));
    recp->num_bits=0;
    recp->flags=0;
    }

BN_RECP_CTX *BN_RECP_CTX_new()
    {
    BN_RECP_CTX *ret;

    if ((ret=(BN_RECP_CTX *)Malloc(sizeof(BN_RECP_CTX))) == NULL)
        return(NULL);

    BN_RECP_CTX_init(ret);
    ret->flags=BN_FLG_MALLOCED;
    return(ret);
    }

void BN_RECP_CTX_free(recp)
BN_RECP_CTX *recp;
    {
    BN_free(&(recp->N));
    BN_free(&(recp->Nr));
    if (recp->flags & BN_FLG_MALLOCED)
        Free(recp);
    }

int BN_RECP_CTX_set(recp,d,ctx)
BN_RECP_CTX *recp;
BIGNUM *d;
BN_CTX *ctx;
    {
    (void)BN_copy(&(recp->N),d);
    (void)BN_zero(&(recp->Nr));
    recp->num_bits=BN_num_bits(d);
    recp->shift=0;
    ctx=ctx;    /* Stop warning */
    return(1);
    }

int BN_mod_mul_reciprocal(r, x, y, recp, ctx)
BIGNUM *r;
BIGNUM *x;
BIGNUM *y;
BN_RECP_CTX *recp;
BN_CTX *ctx;
    {
    int ret=0;
    BIGNUM *a;

    bn_check_top(x);
    bn_check_top(y);

    a= &(ctx->bn[ctx->tos++]);
    if (y != NULL)
        {
        if (x == y)
            { if (!BN_sqr(a,x,ctx)) goto err; }
        else
            { if (!BN_mul(a,x,y,ctx)) goto err; }
        }
    else
        a=x; /* Just do the mod */

    (void)BN_div_recp(NULL,r,a,recp,ctx);
    ret=1;
err:
    ctx->tos--;
    return(ret);
    }

int BN_div_recp(dv,rem,m,recp,ctx)
BIGNUM *dv;
BIGNUM *rem;
BIGNUM *m;
BN_RECP_CTX *recp;
BN_CTX *ctx;
    {
    int i,j,tos,ret=0,ex;
    BIGNUM *a,*b,*d,*r;

    bn_check_top(m);

    tos=ctx->tos;
    a= &(ctx->bn[ctx->tos++]);
    b= &(ctx->bn[ctx->tos++]);
    if (dv != NULL)
        d=dv;
    else
        d= &(ctx->bn[ctx->tos++]);
    if (rem != NULL)
        r=rem;
    else
        r= &(ctx->bn[ctx->tos++]);

    if (BN_ucmp(m,&(recp->N)) < 0)
        {
        (void)BN_zero(d);
        (void)BN_copy(r,m);
        ctx->tos=tos;
        return(1);
        }

    /* We want the remainder
     * Given input of ABCDEF / ab
     * we need multiply ABCDEF by 3 digests of the reciprocal of ab
     *
     */
    i=BN_num_bits(m);

    j=recp->num_bits*2;
    if (j > i)
        {
        i=j;
        ex=0;
        }
    else
        {
        ex=(i-j)/2;
        }

    j=i/2;

    if (i != recp->shift)
        recp->shift=BN_reciprocal(&(recp->Nr),&(recp->N),
            i,ctx);

    if (!BN_rshift(a,m,j-ex)) goto err;
    if (!BN_mul(b,a,&(recp->Nr),ctx)) goto err;
    if (!BN_rshift(d,b,j+ex)) goto err;
    d->neg=0;
    if (!BN_mul(b,&(recp->N),d,ctx)) goto err;
    if (!BN_usub(r,m,b)) goto err;
    r->neg=0;

    j=0;
#if 1
    while (BN_ucmp(r,&(recp->N)) >= 0)
        {
        if (j++ > 2)
            {
#ifndef NO_ERR
            BNerr(BN_F_BN_DIV_RECP,BN_R_BAD_RECIPROCAL);
#endif
            goto err;
            }
        if (!BN_usub(r,r,&(recp->N))) goto err;
        if (!BN_add_word(d,1)) goto err;
        }
#endif

    r->neg=BN_is_zero(r)?0:m->neg;
    d->neg=m->neg^recp->N.neg;
    ret=1;
err:
    ctx->tos=tos;
    return(ret);
    } 

/* len is the expected size of the result
 * We actually calculate with an extra word of precision, so
 * we can do faster division if the remainder is not required.
 */
int BN_reciprocal(r,m,len,ctx)
BIGNUM *r;
BIGNUM *m;
int len;
BN_CTX *ctx;
    {
    int ret= -1;
    BIGNUM t;

    bn_check_top(m);

    BN_init(&t);

    (void)BN_zero(&t);
    if (!BN_set_bit(&t,len)) goto err;

    if (!BN_div(r,NULL,&t,m,ctx)) goto err;
    ret=len;
err:
    BN_free(&t);
    return(ret);
    }