mirror/openssl
2
0
Fork 0
mirror of https://github.com/openssl/openssl.git synced 2024-11-21 01:15:20 +08:00
Code Issues Packages Projects Releases Wiki Activity

bn_mont.c: simplify BN_from_montgomery_word.

Browse Source
This commit is contained in:
Andy Polyakov 2011-10-17 17:24:28 +00:00
parent 79ba545c09
commit 2534891874
1 changed files with 26 additions and 84 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

110
crypto/bn/bn_mont.c
View File

@ -179,24 +179,19 @@ err:
static int BN_from_montgomery_word(BIGNUM *ret, BIGNUM *r, BN_MONT_CTX *mont)
{
BIGNUM *n;
BN_ULONG *ap,*np,*rp,n0,v,*nrp;
int al,nl,max,i,x,ri;
BN_ULONG *ap,*np,*rp,n0,v,carry;
int nl,max,i;
n= &(mont->N);
/* mont->ri is the size of mont->N in bits (rounded up
to the word size) */
al=ri=mont->ri/BN_BITS2;
nl=n->top;
if ((al == 0) || (nl == 0)) { ret->top=0; return(1); }
if (nl == 0) { ret->top=0; return(1); }
max=(nl+al+1); /* allow for overflow (no?) XXX */
max=(2*nl); /* carry is stored separately */
if (bn_wexpand(r,max) == NULL) return(0);
r->neg^=n->neg;
np=n->d;
rp=r->d;
nrp= &(r->d[nl]);
/* clear the top words of T */
#if 1
@ -212,7 +207,7 @@ static int BN_from_montgomery_word(BIGNUM *ret, BIGNUM *r, BN_MONT_CTX *mont)
#ifdef BN_COUNT
fprintf(stderr,"word BN_from_montgomery_word %d * %d\n",nl,nl);
#endif
for (i=0; i<nl; i++)
for (carry=0, i=0; i<nl; i++, rp++)
{
#ifdef __TANDEM
{
@ -230,61 +225,33 @@ static int BN_from_montgomery_word(BIGNUM *ret, BIGNUM *r, BN_MONT_CTX *mont)
#else
v=bn_mul_add_words(rp,np,nl,(rp[0]*n0)&BN_MASK2);
#endif
nrp++;
rp++;
if (((nrp[-1]+=v)&BN_MASK2) >= v)
continue;
if ((rp[nl] = (rp[nl]+v+carry)&BN_MASK2) < v)
carry = 1;
else
{
if (((++nrp[0])&BN_MASK2) != 0) continue;
if (((++nrp[1])&BN_MASK2) != 0) continue;
for (x=2; (((++nrp[x])&BN_MASK2) == 0); x++) ;
}
carry = 0;
}
bn_correct_top(r);
/* mont->ri will be a multiple of the word size and below code
* is kind of BN_rshift(ret,r,mont->ri) equivalent */
if (r->top <= ri)
{
ret->top=0;
return(1);
}
al=r->top-ri;
#define BRANCH_FREE 1
#if BRANCH_FREE
if (bn_wexpand(ret,ri) == NULL) return(0);
x=0-(((al-ri)>>(sizeof(al)*8-1))&1);
ret->top=x=(ri&~x)|(al&x); /* min(ri,al) */
if (bn_wexpand(ret,nl) == NULL) return(0);
ret->top=nl;
ret->neg=r->neg;
rp=ret->d;
ap=&(r->d[ri]);
ap=&(r->d[nl]);
#define BRANCH_FREE 1
#if BRANCH_FREE
{
size_t m1,m2;
BN_ULONG *nrp;
size_t m;
v=bn_sub_words(rp,ap,np,ri);
/* this ----------------^^ works even in al<ri case
* thanks to zealous zeroing of top of the vector in the
* beginning. */
/* if (al==ri && !v) || al>ri) nrp=rp; else nrp=ap; */
/* in other words if subtraction result is real, then
v=bn_sub_words(rp,ap,np,nl)-carry;
/* if subtraction result is real, then
* trick unconditional memcpy below to perform in-place
* "refresh" instead of actual copy. */
m1=0-(size_t)(((al-ri)>>(sizeof(al)*8-1))&1); /* al<ri */
m2=0-(size_t)(((ri-al)>>(sizeof(al)*8-1))&1); /* al>ri */
m1|=m2; /* (al!=ri) */
m1|=(0-(size_t)v); /* (al!=ri || v) */
m1&=~m2; /* (al!=ri || v) && !al>ri */
nrp=(BN_ULONG *)(((PTR_SIZE_INT)rp&~m1)|((PTR_SIZE_INT)ap&m1));
}
m=(0-(size_t)v);
nrp=(BN_ULONG *)(((PTR_SIZE_INT)rp&~m)|((PTR_SIZE_INT)ap&m));
/* 'i<ri' is chosen to eliminate dependency on input data, even
* though it results in redundant copy in al<ri case. */
for (i=0,ri-=4; i<ri; i+=4)
for (i=0,nl-=4; i<nl; i+=4)
{
BN_ULONG t1,t2,t3,t4;
@ -297,40 +264,15 @@ static int BN_from_montgomery_word(BIGNUM *ret, BIGNUM *r, BN_MONT_CTX *mont)
rp[i+2]=t3;
rp[i+3]=t4;
}
for (ri+=4; i<ri; i++)
for (nl+=4; i<nl; i++)
rp[i]=nrp[i], ap[i]=0;
}
#else
if (bn_sub_words (rp,ap,np,nl)-carry)
memcpy(rp,ap,nl*sizeof(BN_ULONG));
#endif
bn_correct_top(r);
bn_correct_top(ret);
#else
if (bn_wexpand(ret,al) == NULL) return(0);
ret->top=al;
ret->neg=r->neg;
rp=ret->d;
ap=&(r->d[ri]);
al-=4;
for (i=0; i<al; i+=4)
{
BN_ULONG t1,t2,t3,t4;
t1=ap[i+0];
t2=ap[i+1];
t3=ap[i+2];
t4=ap[i+3];
rp[i+0]=t1;
rp[i+1]=t2;
rp[i+2]=t3;
rp[i+3]=t4;
}
al+=4;
for (; i<al; i++)
rp[i]=ap[i];
if (BN_ucmp(ret, &(mont->N)) >= 0)
{
if (!BN_usub(ret,ret,&(mont->N))) return(0);
}
#endif
bn_check_top(ret);
return(1);