Commit c91c1ba2b109e0487c7825ef26e173a075f47611
2019-10-24T21:32:31
rework mp_add_d and mp_sub_d
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diff --git a/mp_add_d.c b/mp_add_d.c
index cd0d47a..4508cc8 100644
--- a/mp_add_d.c
+++ b/mp_add_d.c
@@ -11,12 +11,18 @@ mp_err mp_add_d(const mp_int *a, mp_digit b, mp_int *c)
mp_digit *tmpa, *tmpc;
/* fast path for a == c */
- if (a == c &&
- !mp_iszero(c) &&
- c->sign == MP_ZPOS &&
- c->dp[0] + b < MP_DIGIT_MAX) {
- c->dp[0] += b;
- return MP_OKAY;
+ if (a == c) {
+ if ((c->sign == MP_ZPOS) &&
+ !mp_iszero(c) &&
+ ((c->dp[0] + b) < MP_DIGIT_MAX)) {
+ c->dp[0] += b;
+ return MP_OKAY;
+ }
+ if ((c->sign == MP_NEG) &&
+ (c->dp[0] > b)) {
+ c->dp[0] -= b;
+ return MP_OKAY;
+ }
}
/* grow c as required */
diff --git a/mp_sub_d.c b/mp_sub_d.c
index e453d36..96a747c 100644
--- a/mp_sub_d.c
+++ b/mp_sub_d.c
@@ -11,12 +11,17 @@ mp_err mp_sub_d(const mp_int *a, mp_digit b, mp_int *c)
int ix, oldused;
/* fast path for a == c */
- if (a == c &&
- !mp_iszero(c) &&
- c->sign == MP_ZPOS &&
- c->dp[0] > b) {
- c->dp[0] -= b;
- return MP_OKAY;
+ if (a == c) {
+ if ((c->sign == MP_NEG) &&
+ ((c->dp[0] + b) < MP_DIGIT_MAX)) {
+ c->dp[0] += b;
+ return MP_OKAY;
+ }
+ if ((c->sign == MP_ZPOS) &&
+ (c->dp[0] > b)) {
+ c->dp[0] -= b;
+ return MP_OKAY;
+ }
}
/* grow c as required */