From 9080455fae1ce1625d41f5d1f20c5a0448934085 Mon Sep 17 00:00:00 2001
From: Tom Willemse
Date: Mon, 15 Aug 2022 12:17:15 -0700
Subject: Chapter 30.3

---
 clox/src/common.h |  1 +
 clox/src/value.c  | 19 +++++++++++++++++++
 clox/src/value.h  | 45 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 65 insertions(+)

diff --git a/clox/src/common.h b/clox/src/common.h
index bfb76f4..b41797b 100644
--- a/clox/src/common.h
+++ b/clox/src/common.h
@@ -5,6 +5,7 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#define NAN_BOXING
 /* #define DEBUG_PRINT_CODE */
 /* #define DEBUG_TRACE_EXECUTION */
 
diff --git a/clox/src/value.c b/clox/src/value.c
index e442181..8b6cb56 100644
--- a/clox/src/value.c
+++ b/clox/src/value.c
@@ -29,6 +29,17 @@ void freeValueArray(ValueArray *array) {
 }
 
 void printValue(Value value) {
+#ifdef NAN_BOXING
+  if (IS_BOOL(value)) {
+    printf(AS_BOOL(value) ? "true" : "false");
+  } else if (IS_NIL(value)) {
+    printf("nil");
+  } else if (IS_NUMBER(value)) {
+    printf("%g", AS_NUMBER(value));
+  } else if (IS_OBJ(value)) {
+    printObject(value);
+  }
+#else
   switch (value.type) {
   case VAL_BOOL:
     printf(AS_BOOL(value) ? "true" : "false");
@@ -43,9 +54,16 @@ void printValue(Value value) {
     printObject(value);
     break;
   }
+#endif // NAN_BOXING
 }
 
 bool valuesEqual(Value a, Value b) {
+#ifdef NAN_BOXING
+  if (IS_NUMBER(a) && IS_NUMBER(b)) {
+    return AS_NUMBER(a) == AS_NUMBER(b);
+  }
+  return a == b;
+#else
   if (a.type != b.type)
     return false;
   switch (a.type) {
@@ -61,4 +79,5 @@ bool valuesEqual(Value a, Value b) {
   default:
     return false; /* Unreachable */
   }
+#endif // NAN_BOXING
 }
diff --git a/clox/src/value.h b/clox/src/value.h
index 7dbf99e..ea76d86 100644
--- a/clox/src/value.h
+++ b/clox/src/value.h
@@ -1,11 +1,54 @@
 #ifndef clox_value_h
 #define clox_value_h
 
+#include <string.h>
+
 #include "common.h"
 
 typedef struct Obj Obj;
 typedef struct ObjString ObjString;
 
+#ifdef NAN_BOXING
+
+#define SIGN_BIT ((uint64_t)0x8000000000000000)
+#define QNAN ((uint64_t)0x7ffc000000000000)
+
+#define TAG_NIL 1   /* 01 */
+#define TAG_FALSE 2 /* 10 */
+#define TAG_TRUE 3  /* 11 */
+
+typedef uint64_t Value;
+
+#define IS_BOOL(value) (((value) | 1) == TRUE_VAL)
+#define IS_NIL(value) ((value) == NIL_VAL)
+#define IS_NUMBER(value) (((value)&QNAN) != QNAN)
+#define IS_OBJ(value) (((value) & (QNAN | SIGN_BIT)) == (QNAN | SIGN_BIT))
+
+#define AS_BOOL(value) ((value) == TRUE_VAL)
+#define AS_NUMBER(value) valueToNum(value)
+#define AS_OBJ(value) ((Obj *)(uintptr_t)((value) & ~(SIGN_BIT | QNAN)))
+
+#define BOOL_VAL(b) ((b) ? TRUE_VAL : FALSE_VAL)
+#define FALSE_VAL ((Value)(uint64_t)(QNAN | TAG_FALSE))
+#define TRUE_VAL ((Value)(uint64_t)(QNAN | TAG_TRUE))
+#define NIL_VAL ((Value)(uint64_t)(QNAN | TAG_NIL))
+#define NUMBER_VAL(num) numToValue(num)
+#define OBJ_VAL(obj) (Value)(SIGN_BIT | QNAN | (uint64_t)(uintptr_t)(obj))
+
+static inline double valueToNum(Value value) {
+  double num;
+  memcpy(&num, &value, sizeof(Value));
+  return num;
+}
+
+static inline Value numToValue(double num) {
+  Value value;
+  memcpy(&value, &num, sizeof(double));
+  return value;
+}
+
+#else
+
 typedef enum {
   VAL_BOOL,
   VAL_NIL,
@@ -36,6 +79,8 @@ typedef struct {
 #define NUMBER_VAL(value) ((Value){VAL_NUMBER, {.number = value}})
 #define OBJ_VAL(value) ((Value){VAL_OBJ, {.obj = (Obj *)value}})
 
+#endif // NAN_BOXING
+
 typedef struct {
   int capacity;
   int count;
-- 
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