WIP wren/core: Add DEF_NUM_CONSTANT (with Num::infinity and Num::nan). (#781)

* wren/vm: Add "wren_math.h".
* wren/core: Add DEF_NUM_CONSTANT.
* wren/core: Add `Num::infinity` constant.
* wren/core: Add `Num::nan` constant.

doc/site/modules/core/num.markdown

@@ -9,6 +9,16 @@ Attempts to parse `value` as a decimal literal and return it as an instance of
 
 It is a runtime error if `value` is not a string.
 
+### Num.**infinity**
+
+The value of &infinity;.
+
+### Num.**nan**
+
+One value representing a NaN.
+
+Provides a default sane NaN number suitable for the vm internal values.
+
 ### Num.**pi**
 
 The value of π.

src/vm/wren_core.c

@@ -7,6 +7,7 @@
 
 #include "wren_common.h"
 #include "wren_core.h"
+#include "wren_math.h"
 #include "wren_primitive.h"
 #include "wren_value.h"
 
@@ -596,10 +597,19 @@ DEF_PRIMITIVE(num_fromString)
   RETURN_NUM(number);
 }
 
-DEF_PRIMITIVE(num_pi)
-{
-  RETURN_NUM(3.14159265358979323846);
-}
+// Defines a primitive on Num that calls infix [op] and returns [type].
+#define DEF_NUM_CONSTANT(name, value)                                          \
+    DEF_PRIMITIVE(num_##name)                                                  \
+    {                                                                          \
+      RETURN_NUM(value);                                                       \
+    }
+
+DEF_NUM_CONSTANT(infinity, INFINITY)
+DEF_NUM_CONSTANT(nan,      WREN_DOUBLE_NAN)
+DEF_NUM_CONSTANT(pi,       3.14159265358979323846)
+
+DEF_NUM_CONSTANT(largest,  DBL_MAX)
+DEF_NUM_CONSTANT(smallest, DBL_MIN)
 
 // Defines a primitive on Num that calls infix [op] and returns [type].
 #define DEF_NUM_INFIX(name, op, type)                                          \
@@ -749,16 +759,6 @@ DEF_PRIMITIVE(num_sign)
   }
 }
 
-DEF_PRIMITIVE(num_largest)
-{
-  RETURN_NUM(DBL_MAX);
-}
-
-DEF_PRIMITIVE(num_smallest)
-{
-  RETURN_NUM(DBL_MIN);
-}
-
 DEF_PRIMITIVE(num_toString)
 {
   RETURN_VAL(wrenNumToString(vm, AS_NUM(args[0])));
@@ -1277,6 +1277,8 @@ void wrenInitializeCore(WrenVM* vm)
 
   vm->numClass = AS_CLASS(wrenFindVariable(vm, coreModule, "Num"));
   PRIMITIVE(vm->numClass->obj.classObj, "fromString(_)", num_fromString);
+  PRIMITIVE(vm->numClass->obj.classObj, "infinity", num_infinity);
+  PRIMITIVE(vm->numClass->obj.classObj, "nan", num_nan);
   PRIMITIVE(vm->numClass->obj.classObj, "pi", num_pi);
   PRIMITIVE(vm->numClass->obj.classObj, "largest", num_largest);
   PRIMITIVE(vm->numClass->obj.classObj, "smallest", num_smallest);

src/vm/wren_math.h

@@ -0,0 +1,34 @@
+#ifndef wren_math_h
+#define wren_math_h
+
+#include <math.h>
+#include <stdint.h>
+
+// A union to let us reinterpret a double as raw bits and back.
+typedef union
+{
+  uint64_t bits64;
+  uint32_t bits32[2];
+  double num;
+} WrenDoubleBits;
+
+#define WREN_DOUBLE_QNAN_POS_MIN_BITS (UINT64_C(0x7FF8000000000000))
+#define WREN_DOUBLE_QNAN_POS_MAX_BITS (UINT64_C(0x7FFFFFFFFFFFFFFF))
+
+#define WREN_DOUBLE_NAN (wrenDoubleFromBits(WREN_DOUBLE_QNAN_POS_MIN_BITS))
+
+static inline double wrenDoubleFromBits(uint64_t bits)
+{
+  WrenDoubleBits data;
+  data.bits64 = bits;
+  return data.num;
+}
+
+static inline uint64_t wrenDoubleToBits(double num)
+{
+  WrenDoubleBits data;
+  data.num = num;
+  return data.bits64;
+}
+
+#endif

src/vm/wren_value.c

@@ -374,9 +374,7 @@ static inline uint32_t hashBits(uint64_t hash)
 static inline uint32_t hashNumber(double num)
 {
   // Hash the raw bits of the value.
-  DoubleBits bits;
-  bits.num = num;
-  return hashBits(bits.bits64);
+  return hashBits(wrenDoubleToBits(num));
 }
 
 // Generates a hash code for [object].

src/vm/wren_value.h

@@ -5,6 +5,7 @@
 #include <string.h>
 
 #include "wren_common.h"
+#include "wren_math.h"
 #include "wren_utils.h"
 
 // This defines the built-in types and their core representations in memory.
@@ -613,14 +614,6 @@ typedef struct
 
 #endif
 
-// A union to let us reinterpret a double as raw bits and back.
-typedef union
-{
-  uint64_t bits64;
-  uint32_t bits32[2];
-  double num;
-} DoubleBits;
-
 // Creates a new "raw" class. It has no metaclass or superclass whatsoever.
 // This is only used for bootstrapping the initial Object and Class classes,
 // which are a little special.
@@ -854,9 +847,7 @@ static inline Value wrenObjectToValue(Obj* obj)
 static inline double wrenValueToNum(Value value)
 {
 #if WREN_NAN_TAGGING
-  DoubleBits data;
-  data.bits64 = value;
-  return data.num;
+  return wrenDoubleFromBits(value);
 #else
   return value.as.num;
 #endif
@@ -866,9 +857,7 @@ static inline double wrenValueToNum(Value value)
 static inline Value wrenNumToValue(double num)
 {
 #if WREN_NAN_TAGGING
-  DoubleBits data;
-  data.num = num;
-  return data.bits64;
+  return wrenDoubleToBits(num);
 #else
   Value value;
   value.type = VAL_NUM;