int BN_div_recp(BIGNUM *dv, BIGNUM *rem, BIGNUM *m, BN_RECP_CTX *recp,
BN_CTX *ctx)
{
int i,j,ret=0;
BIGNUM *a,*b,*d,*r;
BN_CTX_start(ctx);
a=BN_CTX_get(ctx);
b=BN_CTX_get(ctx);
if (dv != NULL)
d=dv;
else
d=BN_CTX_get(ctx);
if (rem != NULL)
r=rem;
else
r=BN_CTX_get(ctx);
if (a == NULL || b == NULL || d == NULL || r == NULL) goto err;
if (BN_ucmp(m,&(recp->N)) < 0)
{
BN_zero(d);
BN_copy(r,m);
BN_CTX_end(ctx);
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<<1;
if (j>i) i=j;
j>>=1;
if (i != recp->shift)
recp->shift=BN_reciprocal(&(recp->Nr),&(recp->N),
i,ctx);
if (!BN_rshift(a,m,j)) goto err;
if (!BN_mul(b,a,&(recp->Nr),ctx)) goto err;
if (!BN_rshift(d,b,i-j)) 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;
#if 1
j=0;
while (BN_ucmp(r,&(recp->N)) >= 0)
{
if (j++ > 2)
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:
BN_CTX_end(ctx);
return(ret);
}
int BN_div_recp(BIGNUM *dv, BIGNUM *rem, const BIGNUM *m,
BN_RECP_CTX *recp, BN_CTX *ctx)
{
int i, j, ret = 0;
BIGNUM *a, *b, *d, *r;
BN_CTX_start(ctx);
d = (dv != NULL) ? dv : BN_CTX_get(ctx);
r = (rem != NULL) ? rem : BN_CTX_get(ctx);
a = BN_CTX_get(ctx);
b = BN_CTX_get(ctx);
if (b == NULL)
goto err;
if (BN_ucmp(m, &(recp->N)) < 0) {
BN_zero(d);
if (!BN_copy(r, m)) {
BN_CTX_end(ctx);
return 0;
}
BN_CTX_end(ctx);
return 1;
}
/*
* We want the remainder Given input of ABCDEF / ab we need multiply
* ABCDEF by 3 digests of the reciprocal of ab
*/
/* i := max(BN_num_bits(m), 2*BN_num_bits(N)) */
i = BN_num_bits(m);
j = recp->num_bits << 1;
if (j > i)
i = j;
/* Nr := round(2^i / N) */
if (i != recp->shift)
recp->shift = BN_reciprocal(&(recp->Nr), &(recp->N), i, ctx);
/* BN_reciprocal could have returned -1 for an error */
if (recp->shift == -1)
goto err;
/*-
* d := |round(round(m / 2^BN_num_bits(N)) * recp->Nr / 2^(i - BN_num_bits(N)))|
* = |round(round(m / 2^BN_num_bits(N)) * round(2^i / N) / 2^(i - BN_num_bits(N)))|
* <= |(m / 2^BN_num_bits(N)) * (2^i / N) * (2^BN_num_bits(N) / 2^i)|
* = |m/N|
*/
if (!BN_rshift(a, m, recp->num_bits))
goto err;
if (!BN_mul(b, a, &(recp->Nr), ctx))
goto err;
if (!BN_rshift(d, b, i - recp->num_bits))
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;
while (BN_ucmp(r, &(recp->N)) >= 0) {
if (j++ > 2) {
BNerr(BN_F_BN_DIV_RECP, BN_R_BAD_RECIPROCAL);
goto err;
}
if (!BN_usub(r, r, &(recp->N)))
goto err;
if (!BN_add_word(d, 1))
goto err;
}
r->neg = BN_is_zero(r) ? 0 : m->neg;
d->neg = m->neg ^ recp->N.neg;
ret = 1;
err:
BN_CTX_end(ctx);
bn_check_top(dv);
bn_check_top(rem);
return ret;
}
int BN_div_recp(BIGNUM *dv, BIGNUM *rem, const BIGNUM *m,
BN_RECP_CTX *recp, BN_CTX *ctx)
{
int i,j,ret=0;
BIGNUM *a,*b,*d,*r;
BN_CTX_start(ctx);
a=BN_CTX_get(ctx);
b=BN_CTX_get(ctx);
if (dv != NULL)
d=dv;
else
d=BN_CTX_get(ctx);
if (rem != NULL)
r=rem;
else
r=BN_CTX_get(ctx);
if (a == NULL || b == NULL || d == NULL || r == NULL) goto err;
if (BN_ucmp(m,&(recp->N)) < 0)
{
if (!BN_zero(d)) return 0;
if (!BN_copy(r,m)) return 0;
BN_CTX_end(ctx);
return(1);
}
/* We want the remainder
* Given input of ABCDEF / ab
* we need multiply ABCDEF by 3 digests of the reciprocal of ab
*
*/
/* i := max(BN_num_bits(m), 2*BN_num_bits(N)) */
i=BN_num_bits(m);
j=recp->num_bits<<1;
if (j>i) i=j;
/* Nr := round(2^i / N) */
if (i != recp->shift)
recp->shift=BN_reciprocal(&(recp->Nr),&(recp->N),
i,ctx); /* BN_reciprocal returns i, or -1 for an error */
if (recp->shift == -1) goto err;
/* d := |round(round(m / 2^BN_num_bits(N)) * recp->Nr / 2^(i - BN_num_bits(N)))|
* = |round(round(m / 2^BN_num_bits(N)) * round(2^i / N) / 2^(i - BN_num_bits(N)))|
* <= |(m / 2^BN_num_bits(N)) * (2^i / N) * (2^BN_num_bits(N) / 2^i)|
* = |m/N|
*/
if (!BN_rshift(a,m,recp->num_bits)) goto err;
if (!BN_mul(b,a,&(recp->Nr),ctx)) goto err;
if (!BN_rshift(d,b,i-recp->num_bits)) 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;
#if 1
j=0;
while (BN_ucmp(r,&(recp->N)) >= 0)
{
if (j++ > 2)
{
BNerr(BN_F_BN_MOD_MUL_RECIPROCAL,BN_R_BAD_RECIPROCAL);
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:
BN_CTX_end(ctx);
return(ret);
}
