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-rw-r--r--bignum.c12
1 files changed, 12 insertions, 0 deletions
diff --git a/bignum.c b/bignum.c
index bd14002850..cce23273a4 100644
--- a/bignum.c
+++ b/bignum.c
@@ -558,6 +558,18 @@ bigadd(x, y, sign)
if (RBIGNUM(y)->sign == sign) return bigsub(y, x);
return bigsub(x, y);
}
+ else if (sign == 0) {
+ /* x - y */
+ if ((RBIGNUM(x)->sign == 0) && (RBIGNUM(y)->sign == 1)) {
+ /* x is negative and y is positive. */
+ /* return -(abs(x) + y) */
+ VALUE ret;
+ RBIGNUM(x)->sign = 1; /* x = abs(x) */
+ ret = bigadd(x, y, 1); /* ret = x + y (recursive call) */
+ RBIGNUM(ret)->sign = 0; /* ret = -ret */
+ return ret;
+ }
+ }
if (RBIGNUM(x)->len > RBIGNUM(y)->len) {
len = RBIGNUM(x)->len + 1;