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

Add functions for safe addition and subtraction

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

src/numeric.c

@@ -1109,9 +1109,7 @@ mrb_fixnum_plus(mrb_state *mrb, mrb_value x, mrb_value y)
 
     if (a == 0) return y;
     b = mrb_fixnum(y);
-    c = a + b;
-    if (((a < 0) ^ (b < 0)) == 0 && (a < 0) != (c < 0)) {
-      /* integer overflow */
+    if (mrb_int_add_overflow(a, b, &c)) {
       return mrb_float_value(mrb, (mrb_float)a + (mrb_float)b);
     }
     return mrb_fixnum_value(c);
@@ -1147,9 +1145,7 @@ mrb_fixnum_minus(mrb_state *mrb, mrb_value x, mrb_value y)
     mrb_int b, c;
 
     b = mrb_fixnum(y);
-    c = a - b;
-    if (((a < 0) ^ (b < 0)) != 0 && (a < 0) != (c < 0)) {
-      /* integer overflow */
+    if (mrb_int_sub_overflow(a, b, &c)) {
       return mrb_float_value(mrb, (mrb_float)a - (mrb_float)b);
     }
     return mrb_fixnum_value(c);

src/vm.c

@@ -12,6 +12,7 @@
 #include "mruby/class.h"
 #include "mruby/hash.h"
 #include "mruby/irep.h"
+#include "mruby/numeric.h"
 #include "mruby/proc.h"
 #include "mruby/range.h"
 #include "mruby/string.h"
@@ -1610,12 +1611,7 @@ RETRY_TRY_BLOCK:
 
           x = mrb_fixnum(regs_a[0]);
           y = mrb_fixnum(regs_a[1]);
-          z = x + y;
-#ifdef MRB_WORD_BOXING
-          z = (z << MRB_FIXNUM_SHIFT) / (1 << MRB_FIXNUM_SHIFT);
-#endif
-          if ((x < 0) != (z < 0) && ((x < 0) ^ (y < 0)) == 0) {
-            /* integer overflow */
+          if (mrb_int_add_overflow(x, y, &z)) {
             SET_FLT_VALUE(mrb, regs_a[0], (mrb_float)x + (mrb_float)y);
             break;
           }
@@ -1673,12 +1669,7 @@ RETRY_TRY_BLOCK:
 
           x = mrb_fixnum(regs[a]);
           y = mrb_fixnum(regs[a+1]);
-          z = x - y;
-#ifdef MRB_WORD_BOXING
-          z = (z << MRB_FIXNUM_SHIFT) / (1 << MRB_FIXNUM_SHIFT);
-#endif
-          if (((x < 0) ^ (y < 0)) != 0 && (x < 0) != (z < 0)) {
-            /* integer overflow */
+          if (mrb_int_sub_overflow(x, y, &z)) {
             SET_FLT_VALUE(mrb, regs[a], (mrb_float)x - (mrb_float)y);
             break;
           }
@@ -1842,10 +1833,9 @@ RETRY_TRY_BLOCK:
         {
           mrb_int x = regs[a].attr_i;
           mrb_int y = GETARG_C(i);
-          mrb_int z = x + y;
+          mrb_int z;
 
-          if (((x < 0) ^ (y < 0)) == 0 && (x < 0) != (z < 0)) {
-            /* integer overflow */
+          if (mrb_int_add_overflow(x, y, &z)) {
             SET_FLT_VALUE(mrb, regs[a], (mrb_float)x + (mrb_float)y);
             break;
           }
@@ -1881,10 +1871,9 @@ RETRY_TRY_BLOCK:
         {
           mrb_int x = regs_a[0].attr_i;
           mrb_int y = GETARG_C(i);
-          mrb_int z = x - y;
+          mrb_int z;
 
-          if ((x < 0) != (z < 0) && ((x < 0) ^ (y < 0)) != 0) {
-            /* integer overflow */
+          if (mrb_int_sub_overflow(x, y, &z)) {
             SET_FLT_VALUE(mrb, regs_a[0], (mrb_float)x - (mrb_float)y);
           }
           else {