Use carry flag to reduce instructions

NOTE:
(1) Fixnum's LSB is always 1.
    It means you can always run `x - 1` without overflow.
(2) Of course `z = x + (y-1)` may overflow.
    Now z's LSB is always 1, and the MSB of true result is also 1.
    You can get true result in long as `(1<<63)|(z>>1)`,
    and it equals to `(z<<63)|(z>>1)` == `ror(z)`.

GCC and Clang have __builtin_add_ovewflow:
* https://gcc.gnu.org/onlinedocs/gcc/Integer-Overflow-Builtins.html
* https://clang.llvm.org/docs/LanguageExtensions.html#checked-arithmetic-builtins

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57506 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 2 insertions, 18 deletions

diff --git a/numeric.c b/numeric.c
index 5f67214cba..1a685ed252 100644
--- a/numeric.c
+++ b/numeric.c
@@ -3458,15 +3458,7 @@ static VALUE
 fix_plus(VALUE x, VALUE y)
 {
     if (FIXNUM_P(y)) {
-	long a, b, c;
-	VALUE r;
-
-	a = FIX2LONG(x);
-	b = FIX2LONG(y);
-	c = a + b;
-	r = LONG2NUM(c);
-
-	return r;
+	return rb_fix_plus_fix(x, y);
     }
     else if (RB_TYPE_P(y, T_BIGNUM)) {
 	return rb_big_plus(y, x);
@@ -3513,15 +3505,7 @@ static VALUE
 fix_minus(VALUE x, VALUE y)
 {
     if (FIXNUM_P(y)) {
-	long a, b, c;
-	VALUE r;
-
-	a = FIX2LONG(x);
-	b = FIX2LONG(y);
-	c = a - b;
-	r = LONG2NUM(c);
-
-	return r;
+	return rb_fix_minus_fix(x, y);
     }
     else if (RB_TYPE_P(y, T_BIGNUM)) {
 	x = rb_int2big(FIX2LONG(x));