Add Num.[max/min]SafeInteger (#874)

wren-lang · Apr 8, 2021 · 28da4b4 · 28da4b4
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diff --git a/doc/site/modules/core/num.markdown b/doc/site/modules/core/num.markdown
@@ -35,6 +35,17 @@ The largest representable numeric value.
 
 The smallest positive representable numeric value.
 
+### Num.**maxSafeInteger**
+
+The largest integer that Wren can safely represent. It's a constant value of `9007199254740991`.
+
+ This is relevant because Wren uses double precision [floating-point format](https://en.wikipedia.org/wiki/IEEE_floating_point)
+ for numbers, which can only safely represent integers between <code>-(2<sup>53</sup> - 1)</code> and <code>2<sup>53</sup> - 1</code>.
+
+### Num.**minSafeInteger**
+
+The smallest integer Wren can safely represent. It's a constant value of `-9007199254740991`. 
+
 ## Methods
 
 ### **abs**

diff --git a/src/vm/wren_core.c b/src/vm/wren_core.c
@@ -640,6 +640,9 @@ DEF_NUM_CONSTANT(tau,      6.28318530717958647692528676655900577)
 DEF_NUM_CONSTANT(largest,  DBL_MAX)
 DEF_NUM_CONSTANT(smallest, DBL_MIN)
 
+DEF_NUM_CONSTANT(maxSafeInteger, 9007199254740991.0)
+DEF_NUM_CONSTANT(minSafeInteger, -9007199254740991.0)
+
 // Defines a primitive on Num that calls infix [op] and returns [type].
 #define DEF_NUM_INFIX(name, op, type)                                          \
     DEF_PRIMITIVE(num_##name)                                                  \
@@ -1336,6 +1339,8 @@ void wrenInitializeCore(WrenVM* vm)
   PRIMITIVE(vm->numClass->obj.classObj, "tau", num_tau);
   PRIMITIVE(vm->numClass->obj.classObj, "largest", num_largest);
   PRIMITIVE(vm->numClass->obj.classObj, "smallest", num_smallest);
+  PRIMITIVE(vm->numClass->obj.classObj, "maxSafeInteger", num_maxSafeInteger);
+  PRIMITIVE(vm->numClass->obj.classObj, "minSafeInteger", num_minSafeInteger);
   PRIMITIVE(vm->numClass, "-(_)", num_minus);
   PRIMITIVE(vm->numClass, "+(_)", num_plus);
   PRIMITIVE(vm->numClass, "*(_)", num_multiply);

diff --git a/test/core/number/maxSafeInteger.wren b/test/core/number/maxSafeInteger.wren
@@ -0,0 +1 @@
+System.print(Num.maxSafeInteger) // expect: 9.007199254741e+15
diff --git a/test/core/number/minSafeInteger.wren b/test/core/number/minSafeInteger.wren
@@ -0,0 +1 @@
+System.print(Num.minSafeInteger) // expect: -9.007199254741e+15