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