Add a comment to explain the purpose of bn_cmp_part_words().

[openssl.git] / crypto / bn / bn_exp.c

diff --git a/crypto/bn/bn_exp.c b/crypto/bn/bn_exp.c
index f7e7ced2ca0840973aa205f6323b7eccf4ee9f49..1739be68645b4af678d6609ead457b0df05d1765 100644 (file)
--- a/crypto/bn/bn_exp.c
+++ b/crypto/bn/bn_exp.c
@@ -191,6 +191,7 @@ int BN_mod_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
         */
 
 #define MONT_MUL_MOD
+#define MONT_EXP_WORD
 #define RECP_MUL_MOD
 
 #ifdef MONT_MUL_MOD
@@ -202,14 +203,14 @@ int BN_mod_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
 
        if (BN_is_odd(m))
                {
+#  ifdef MONT_EXP_WORD
                if (a->top == 1 && !a->neg)
                        {
                        BN_ULONG A = a->d[0];
-                       if (m->top == 1)
-                               A %= m->d[0]; /* make sure that A is reduced */
                        ret=BN_mod_exp_mont_word(r,A,p,m,ctx,NULL);
                        }
                else
+#  endif
                        ret=BN_mod_exp_mont(r,a,p,m,ctx,NULL);
                }
        else
@@ -505,11 +506,14 @@ int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p,
        bn_check_top(p);
        bn_check_top(m);
 
-       if (!(m->d[0] & 1))
+       if (m->top == 0 || !(m->d[0] & 1))
                {
                BNerr(BN_F_BN_MOD_EXP_MONT_WORD,BN_R_CALLED_WITH_EVEN_MODULUS);
                return(0);
                }
+       if (m->top == 1)
+               a %= m->d[0]; /* make sure that 'a' is reduced */
+
        bits = BN_num_bits(p);
        if (bits == 0)
                {
@@ -642,8 +646,8 @@ int BN_mod_exp_simple(BIGNUM *r,
        if (!BN_nnmod(&(val[0]),a,m,ctx)) goto err;             /* 1 */
        if (BN_is_zero(&(val[0])))
                {
-               ret = BN_one(r);
-               return ret;
+               ret = BN_zero(r);
+               goto err;
                }
 
        window = BN_window_bits_for_exponent_size(bits);