Commit 88af716e authored by Andy Polyakov's avatar Andy Polyakov
Browse files

bn/bn_mont.c: improve readability of post-condition code. 



Reviewed-by: default avatarRich Salz <rsalz@openssl.org>
Reviewed-by: default avatarDavid Benjamin <davidben@google.com>
(Merged from https://github.com/openssl/openssl/pull/6662)

(cherry picked from commit 6c90182a)
parent 308447e3

crypto/bn/bn_mont.c

+5 −6
Original line number Diff line number Diff line
@@ -130,15 +130,14 @@ static int BN_from_montgomery_word(BIGNUM *ret, BIGNUM *r, BN_MONT_CTX *mont) 
     */

    ap = &(r->d[nl]);



    carry -= bn_sub_words(rp, ap, np, nl);

    /*

     * |v| is one if |ap| - |np| underflowed or zero if it did not. Note |v|

     * cannot be -1. That would imply the subtraction did not fit in |nl| words,

     * and we know at most one subtraction is needed.

     * |carry| is -1 if |ap| - |np| underflowed or zero if it did not. Note

     * |carry| cannot be 1. That would imply the subtraction did not fit in

     * |nl| words, and we know at most one subtraction is needed.

     */

    v = bn_sub_words(rp, ap, np, nl) - carry;

    v = 0 - v;

    for (i = 0; i < nl; i++) {

        rp[i] = (v & ap[i]) | (~v & rp[i]);

        rp[i] = (carry & ap[i]) | (~carry & rp[i]);

        ap[i] = 0;

    }

    bn_correct_top(r);