int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor,
BN_CTX *ctx)
{
- int norm_shift,i,j,loop;
+ int norm_shift,i,loop;
BIGNUM *tmp,wnum,*snum,*sdiv,*res;
BN_ULONG *resp,*wnump;
BN_ULONG d0,d1;
int num_n,div_n;
+ if (dv)
+ bn_check_top(dv);
+ if (rm)
+ bn_check_top(rm);
bn_check_top(num);
bn_check_top(divisor);
res=BN_CTX_get(ctx);
else res=dv;
if (sdiv == NULL || res == NULL) goto err;
- tmp->neg=0;
/* First we normalise the numbers */
norm_shift=BN_BITS2-((BN_num_bits(divisor))%BN_BITS2);
div_n=sdiv->top;
num_n=snum->top;
loop=num_n-div_n;
-
/* Lets setup a 'window' into snum
* This is the part that corresponds to the current
* 'area' being divided */
- BN_init(&wnum);
- wnum.d= &(snum->d[loop]);
- wnum.top= div_n;
- wnum.dmax= snum->dmax+1; /* a bit of a lie */
+ wnum.neg = 0;
+ wnum.d = &(snum->d[loop]);
+ wnum.top = div_n;
+ /* only needed when BN_ucmp messes up the values between top and max */
+ wnum.dmax = snum->dmax - loop; /* so we don't step out of bounds */
/* Get the top 2 words of sdiv */
- /* i=sdiv->top; */
+ /* div_n=sdiv->top; */
d0=sdiv->d[div_n-1];
d1=(div_n == 1)?0:sdiv->d[div_n-2];
if (BN_ucmp(&wnum,sdiv) >= 0)
{
- if (!BN_usub(&wnum,&wnum,sdiv)) goto err;
+ /* If BN_DEBUG_RAND is defined BN_ucmp changes (via
+ * bn_pollute) the const bignum arguments =>
+ * clean the values between top and max again */
+ bn_clear_top2max(&wnum);
+ bn_sub_words(wnum.d, wnum.d, sdiv->d, div_n);
*resp=1;
- res->d[res->top-1]=1;
}
else
res->top--;
+ /* if res->top == 0 then clear the neg value otherwise decrease
+ * the resp pointer */
if (res->top == 0)
res->neg = 0;
- resp--;
+ else
+ resp--;
- for (i=0; i<loop-1; i++)
+ for (i=0; i<loop-1; i++, wnump--, resp--)
{
BN_ULONG q,l0;
+ /* the first part of the loop uses the top two words of
+ * snum and sdiv to calculate a BN_ULONG q such that
+ * | wnum - sdiv * q | < sdiv */
#if defined(BN_DIV3W) && !defined(OPENSSL_NO_ASM)
BN_ULONG bn_div_3_words(BN_ULONG*,BN_ULONG,BN_ULONG);
q=bn_div_3_words(wnump,d1,d0);
#endif /* !BN_DIV3W */
l0=bn_mul_words(tmp->d,sdiv->d,div_n,q);
- wnum.d--; wnum.top++;
tmp->d[div_n]=l0;
- for (j=div_n+1; j>0; j--)
- if (tmp->d[j-1]) break;
- tmp->top=j;
-
- j=wnum.top;
- if (!BN_sub(&wnum,&wnum,tmp)) goto err;
-
- snum->top=snum->top+wnum.top-j;
-
- if (wnum.neg)
+ wnum.d--;
+ /* ingore top values of the bignums just sub the two
+ * BN_ULONG arrays with bn_sub_words */
+ if (bn_sub_words(wnum.d, wnum.d, tmp->d, div_n+1))
{
+ /* Note: As we have considered only the leading
+ * two BN_ULONGs in the calculation of q, sdiv * q
+ * might be greater than wnum (but then (q-1) * sdiv
+ * is less or equal than wnum)
+ */
q--;
- j=wnum.top;
- if (!BN_add(&wnum,&wnum,sdiv)) goto err;
- snum->top+=wnum.top-j;
+ if (bn_add_words(wnum.d, wnum.d, sdiv->d, div_n))
+ /* we can't have an overflow here (assuming
+ * that q != 0, but if q == 0 then tmp is
+ * zero anyway) */
+ (*wnump)++;
}
- *(resp--)=q;
- wnump--;
+ /* store part of the result */
+ *resp = q;
}
+ bn_correct_top(snum);
if (rm != NULL)
{
/* Keep a copy of the neg flag in num because if rm==num
BN_rshift(rm,snum,norm_shift);
if (!BN_is_zero(rm))
rm->neg = neg;
+ bn_check_top(rm);
}
BN_CTX_end(ctx);
return(1);
err:
+ if (rm)
+ bn_check_top(rm);
BN_CTX_end(ctx);
return(0);
}