Merge pull request #2200 from cremno/add-functions-for-safe-addition-and-subtraction

Add functions for safe addition and subtraction

1 files changed, 35 insertions, 0 deletions

diff --git a/include/mruby/numeric.h b/include/mruby/numeric.h
index 17291c2f2..fe4f3b264 100644
--- a/include/mruby/numeric.h
+++ b/include/mruby/numeric.h
@@ -25,6 +25,41 @@ mrb_value mrb_fixnum_mul(mrb_state *mrb, mrb_value x, mrb_value y);
 mrb_value mrb_num_div(mrb_state *mrb, mrb_value x, mrb_value y);
 mrb_float mrb_to_flo(mrb_state *mrb, mrb_value x);
 
+#define MRB_UINT_MAKE2(n) uint ## n ## _t
+#define MRB_UINT_MAKE(n) MRB_UINT_MAKE2(n)
+#define mrb_uint MRB_UINT_MAKE(MRB_INT_BIT)
+
+#ifdef MRB_WORD_BOXING
+# define MRB_INT_OVERFLOW_MASK ((mrb_uint)1 << (MRB_INT_BIT - 1 - MRB_FIXNUM_SHIFT))
+#else
+# define MRB_INT_OVERFLOW_MASK ((mrb_uint)1 << (MRB_INT_BIT - 1))
+#endif
+
+static inline mrb_bool
+mrb_int_add_overflow(mrb_int augend, mrb_int addend, mrb_int *sum)
+{
+  mrb_uint x = (mrb_uint)augend;
+  mrb_uint y = (mrb_uint)addend;
+  mrb_uint z = (mrb_uint)(x + y);
+  *sum = (mrb_int)z;
+  return !!(((x ^ z) & (y ^ z)) & MRB_INT_OVERFLOW_MASK);
+}
+
+static inline mrb_bool
+mrb_int_sub_overflow(mrb_int minuend, mrb_int subtrahend, mrb_int *difference)
+{
+  mrb_uint x = (mrb_uint)minuend;
+  mrb_uint y = (mrb_uint)subtrahend;
+  mrb_uint z = (mrb_uint)(x - y);
+  *difference = (mrb_int)z;
+  return !!(((x ^ z) & (~y ^ z)) & MRB_INT_OVERFLOW_MASK);
+}
+
+#undef MRB_INT_OVERFLOW_MASK
+#undef mrb_uint
+#undef MRB_UINT_MAKE
+#undef MRB_UINT_MAKE2
+
 #if defined(__cplusplus)
 }  /* extern "C" { */
 #endif