diff options
author | Andy Polyakov <appro@openssl.org> | 2007-06-11 08:53:52 +0000 |
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committer | Andy Polyakov <appro@openssl.org> | 2007-06-11 08:53:52 +0000 |
commit | c693b5a55c627f08b3d2bb23d5f103291c0e7d70 (patch) | |
tree | dd26627835d5d5e8c94ef2e6a92d59a259af878d /crypto/bn/bn_mont.c | |
parent | 6b6443dead7b8c691ec8b3ae135ad989bbb1c3a1 (diff) |
Commentary updates and minor optimization for bn_mont.c.
Diffstat (limited to 'crypto/bn/bn_mont.c')
-rw-r--r-- | crypto/bn/bn_mont.c | 20 |
1 files changed, 13 insertions, 7 deletions
diff --git a/crypto/bn/bn_mont.c b/crypto/bn/bn_mont.c index 594d95940f..4339aab187 100644 --- a/crypto/bn/bn_mont.c +++ b/crypto/bn/bn_mont.c @@ -270,18 +270,24 @@ static int BN_from_montgomery_word(BIGNUM *ret, BIGNUM *r, BN_MONT_CTX *mont) size_t m1,m2; v=bn_sub_words(rp,ap,mont->N.d,ri); - /* if (al==ri && !v) || al>ri) nrp=rp; */ + /* 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 - * trick unconditional memcpy below to make "refresh" - * instead of real copy. */ + * 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=~(m1|m2); /* (al==ri) */ - m1&=~(0-(size_t)v); /* (al==ri && !v) */ - m1|=m2; /* (al==ri && !v) || al>ri */ - nrp=(BN_ULONG *)(((size_t)rp&m1)|((size_t)ap&~m1)); + m1|=m2; /* (al!=ri) */ + m1|=(0-(size_t)v); /* (al!=ri || v) */ + m1&=~m2; /* (al!=ri || v) && !al>ri */ + nrp=(BN_ULONG *)(((size_t)rp&~m1)|((size_t)ap&m1)); } + /* '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) { BN_ULONG t1,t2,t3,t4; |