Merge pull request #11 from carpentry-org/claude/lua-double-numbers

carry Lua numbers as doubles

Author: hellerve

README.md

@@ -36,14 +36,22 @@ state and closes it when the block exits:
 ```
 
 The `Lua` module wraps the Lua C API directly: stack operations
-(`push-int`, `push-float`, `push-bool`, `push-string`, `get-int`, etc.),
+(`push-int`, `push-double`, `push-bool`, `push-string`, `get-int`, etc.),
 globals (`get-global`, `set-global`), tables (`create-table`, `set-field`,
 `get-field`, `next`), code execution (`do-string`, `do-file`, `call`), and
 type checking (`type-of`, `TYPE_NIL`, `TYPE_NUMBER`, etc.). It also provides a
 few conveniences: `Lua.fun` for defining Lua functions inline, `Lua.val` for
 evaluating Lua expressions into globals, and `Lua.eval-file` for loading Lua
 files with error handling.
 
+A Lua number is a C double, so `push-double` and `get-double` (and the matching
+`Luax.set-double-global`, `Luax.get-double-field`, …) carry Lua floats at full
+precision. The `float` versions still work — a float widens into a double
+exactly — but `get-float` narrows on the way back, so reading through it drops
+everything past single precision. Lua integers are a separate 64-bit subtype;
+`get-double` converts them to doubles, so integers above 2^53 are no longer all
+exactly representable and may come back rounded.
+
 The `Luax` module provides safe wrappers that return `Maybe` and `Result`
 types instead of requiring manual type checks:
 
@@ -58,8 +66,8 @@ types instead of requiring manual type checks:
 (Luax.make-table lua player
   (name (Lua.push-carp-str "Ada"))
   (hp (Lua.push-int 100))
-  (x (Lua.push-float 3.5f))
-  (y (Lua.push-float 7.0f)))
+  (x (Lua.push-double 3.5))
+  (y (Lua.push-double 7.0)))
 
 ; read table fields — returns Maybe, keeps the stack clean
 (Lua.get-global lua (cstr "player"))

lua.carp

@@ -163,8 +163,10 @@ automatically.")
   (register push-light-user-data (Fn [&Lua (Ptr ())] ()) "lua_pushlightuserdata")
   (doc push-nil "Push nil onto the stack.")
   (register push-nil (Fn [&Lua] ()) "lua_pushnil")
-  (doc push-float "Push a float (Lua number) onto the stack.")
-  (register push-float (Fn [&Lua Float] ()) "lua_pushnumber")
+  (doc push-double "Push a double (Lua number) onto the stack.")
+  (register push-double (Fn [&Lua Double] ()) "lua_pushnumber")
+  (doc push-float "Push a float onto the stack as a Lua number.")
+  (defn push-float [lua f] (push-double lua (Double.from-float f)))
   (doc push-string "Push a C string onto the stack. For Carp strings, use
 [`push-carp-str`](#push-carp-str) instead.")
   (deftemplate push-string
@@ -189,9 +191,13 @@ elements on the stack.")
   (doc get-int "Read the value at `index` as an integer. Does not check the
 type—use [`Luax.maybe-get-int`](#maybe-get-int) for a safe version.")
   (register get-int (Fn [&Lua Int] Int) "lua_tointeger")
-  (doc get-float "Read the value at `index` as a float. Does not check the
+  (doc get-double "Read the value at `index` as a double. Does not check the
+type—use [`Luax.maybe-get-double`](#maybe-get-double) for a safe version.")
+  (register get-double (Fn [&Lua Int] Double) "lua_tonumber")
+  (doc get-float "Read the value at `index` as a float. Lua numbers are doubles,
+so this narrows; use [`get-double`](#get-double) instead. Does not check the
 type—use [`Luax.maybe-get-float`](#maybe-get-float) for a safe version.")
-  (register get-float (Fn [&Lua Int] Float) "lua_tonumber")
+  (defn get-float [lua index] (Double.to-float (get-double lua index)))
   (doc get-string "Read the value at `index` as a C string pointer. Returns a
 raw pointer; prefer [`Luax.get-carp-str`](#get-carp-str) or
 [`Luax.maybe-get-string`](#maybe-get-string) for safe access.")
@@ -595,30 +601,35 @@ the Lua standard library available.
 ```
 
 Values are passed between Carp and Lua through the stack. Push values with
-[`push-int`](#push-int), [`push-float`](#push-float),
+[`push-int`](#push-int), [`push-double`](#push-double),
 [`push-bool`](#push-bool), [`push-carp-str`](#push-carp-str), etc. Read them
-back with [`get-int`](#get-int), [`get-float`](#get-float), and so on, using
+back with [`get-int`](#get-int), [`get-double`](#get-double), and so on, using
 negative indices to address from the top of the stack (-1 is the top element).
 
 ```
 ; push two values, read the top one
 (Lua.push-int lua 42)
-(Lua.push-float lua 3.14f)
-(let [f (Lua.get-float lua -1)   ; 3.14
-      i (Lua.get-int lua -2)]    ; 42
+(Lua.push-double lua 3.14)
+(let [d (Lua.get-double lua -1)   ; 3.14
+      i (Lua.get-int lua -2)]     ; 42
   (Lua.pop lua 2))
 ```
 
+A Lua number is a C double. [`push-float`](#push-float) widens exactly, but
+[`get-float`](#get-float) narrows on the way back, so a number read through it
+loses everything past single precision and anything above the float range comes
+back as an infinity.
+
 To call a Lua function at the low level, push the function, then its arguments,
 then use [`call`](#call) with the argument and result counts. The result
 replaces the function and arguments on the stack.
 
 ```
 (Lua.get-global lua (cstr \"math\"))
 (ignore (Lua.get-field lua -1 (cstr \"sqrt\")))
-(Lua.push-float lua 9.0f)
+(Lua.push-double lua 9.0)
 (ignore (Lua.call lua 1 1 0))
-(IO.println &(str (Lua.get-float lua -1)))  ; 3.0
+(IO.println &(str (Lua.get-double lua -1)))  ; 3.0
 (Lua.pop lua 2)  ; pop result and math table
 ```
 
@@ -782,6 +793,11 @@ and assigns it to a global in one expression:
     (String.from-cstr-or (Lua.to-string lua index) @""))
 
   (luax--def-maybe-get int Lua.TYPE_NUMBER Lua.get-int "an integer" "a number")
+  (luax--def-maybe-get double
+                       Lua.TYPE_NUMBER
+                       Lua.get-double
+                       "a double"
+                       "a number")
   (luax--def-maybe-get float Lua.TYPE_NUMBER Lua.get-float "a float" "a number")
   (luax--def-maybe-get bool
                        Lua.TYPE_BOOLEAN
@@ -804,6 +820,7 @@ unchanged.")
         (Maybe.Nothing))))
 
   (luax--def-set-global int Lua.push-int)
+  (luax--def-set-global double Lua.push-double)
   (luax--def-set-global float Lua.push-float)
   (luax--def-set-global bool Lua.push-bool)
   ; `string` is defined explicitly rather than via luax--def-set-global: the
@@ -814,6 +831,11 @@ unchanged.")
     (do (Lua.push-carp-str lua value) (Lua.set-global lua (cstr name))))
 
   (luax--def-get-global int Lua.TYPE_NUMBER Lua.get-int "an integer" "a number")
+  (luax--def-get-global double
+                        Lua.TYPE_NUMBER
+                        Lua.get-double
+                        "a double"
+                        "a number")
   (luax--def-get-global float Lua.TYPE_NUMBER Lua.get-float "a float" "a number")
   (luax--def-get-global bool
                         Lua.TYPE_BOOLEAN
@@ -833,11 +855,17 @@ unchanged.")
         result)))
 
   (luax--def-set-field int Lua.push-int)
+  (luax--def-set-field double Lua.push-double)
   (luax--def-set-field float Lua.push-float)
   (luax--def-set-field bool Lua.push-bool)
   (luax--def-set-field string Lua.push-carp-str)
 
   (luax--def-get-field int Lua.TYPE_NUMBER Lua.get-int "an integer" "a number")
+  (luax--def-get-field double
+                       Lua.TYPE_NUMBER
+                       Lua.get-double
+                       "a double"
+                       "a number")
   (luax--def-get-field float Lua.TYPE_NUMBER Lua.get-float "a float" "a number")
   (luax--def-get-field bool
                        Lua.TYPE_BOOLEAN

test/lua.carp

@@ -48,6 +48,59 @@
     2.5f
     (Lua.with-lua-do (Lua.push-float lua 2.5f) (Lua.get-float lua -1))
     "push-float / get-float round-trip")
+  (assert-equal test
+    3.1415926535897931
+    (Lua.with-lua-do (Lua.push-double lua 3.1415926535897931)
+                     (Lua.get-double lua -1))
+    "push-double / get-double round-trip keeps all 17 significant digits")
+  (assert-equal test
+    16777217.0
+    (Lua.with-lua-do (Lua.libs lua)
+                     (ignore (Luax.do-in lua "n = 16777217"))
+                     (Lua.get-global lua (cstr "n"))
+                     (Lua.get-double lua -1))
+    "get-double reads a Lua integer above 2^24 intact")
+  (assert-true test
+    (let [n (Lua.with-lua-do (Lua.libs lua)
+                             (ignore (Luax.do-in lua "n = 1e300"))
+                             (Lua.get-global lua (cstr "n"))
+                             (Lua.get-double lua -1))]
+      (and (Double.> n 0.0) (Double.< n Double.MAX)))
+    "get-double reads 1e300 as a finite value")
+  (assert-true test
+    (let [n (Lua.with-lua-do (Lua.libs lua)
+                             (ignore (Luax.do-in lua "n = -1e300"))
+                             (Lua.get-global lua (cstr "n"))
+                             (Lua.get-double lua -1))]
+      (and (Double.< n 0.0) (Double.> n (Double.neg Double.MAX))))
+    "get-double reads -1e300 as a finite value")
+  (assert-equal test
+    3.1415926535897931
+    (Lua.with-lua-do (Lua.libs lua)
+                     (Lua.push-double lua 3.1415926535897931)
+                     (Lua.set-global lua (cstr "n"))
+                     (ignore (Luax.do-in lua "n = n * 2 / 2"))
+                     (Lua.get-global lua (cstr "n"))
+                     (Lua.get-double lua -1))
+    "push-double hands Lua the full value")
+
+  (assert-equal test
+    (Double.to-float 3.1415926535897931)
+    (Lua.with-lua-do (Lua.push-double lua 3.1415926535897931)
+                     (Lua.get-float lua -1))
+    "get-float still narrows to single precision")
+  (assert-true test
+    (Float.>
+      (Lua.with-lua-do (Lua.libs lua)
+                       (ignore (Luax.do-in lua "n = 1e300"))
+                       (Lua.get-global lua (cstr "n"))
+                       (Lua.get-float lua -1))
+      Float.MAX)
+    "get-float still overflows past the float range")
+  (assert-equal test
+    (Double.from-float 2.5f)
+    (Lua.with-lua-do (Lua.push-float lua 2.5f) (Lua.get-double lua -1))
+    "push-float still accepts a Float")
   (assert-true test
     (Lua.with-lua-do (Lua.push-bool lua true) (Lua.get-bool lua -1))
     "push-bool true round-trip")

test/midlevel.carp

@@ -31,6 +31,22 @@
       &(Lua.with-lua-do (Lua.push-bool lua true) (Luax.maybe-get-float lua -1)))
     "maybe-get-float returns Nothing for boolean value")
 
+  (assert-true test
+    (= &(Maybe.Just 3.1415926535897931)
+       &(Lua.with-lua-do (Lua.push-double lua 3.1415926535897931)
+                         (Luax.maybe-get-double lua -1)))
+    "maybe-get-double returns Just for number value")
+  (assert-true test
+    (Maybe.nothing?
+      &(Lua.with-lua-do (Lua.push-bool lua true) (Luax.maybe-get-double lua -1)))
+    "maybe-get-double returns Nothing for boolean value")
+  (assert-true test
+    (Maybe.nothing?
+      &(Lua.with-lua-do
+        (ignore (Lua.push-string lua (cstr "hello")))
+        (Luax.maybe-get-double lua -1)))
+    "maybe-get-double returns Nothing for string value")
+
   (assert-true test
     (= &(Maybe.Just true)
        &(Lua.with-lua-do (Lua.push-bool lua true) (Luax.maybe-get-bool lua -1)))
@@ -191,6 +207,22 @@
                      (Lua.get-float lua -1))
     "set-float-global sets a float global")
 
+  (assert-equal test
+    3.1415926535897931
+    (Lua.with-lua-do (Lua.libs lua)
+                     (Luax.set-double-global lua "d" 3.1415926535897931)
+                     (Lua.get-global lua (cstr "d"))
+                     (Lua.get-double lua -1))
+    "set-double-global sets a double global without losing precision")
+  (assert-true test
+    (let [n (Lua.with-lua-do (Lua.libs lua)
+                             (ignore (Luax.do-in lua "d = 1e300"))
+                             (ignore (Luax.do-in lua "d = d + 0"))
+                             (Lua.get-global lua (cstr "d"))
+                             (Lua.get-double lua -1))]
+      (and (Double.> n 0.0) (Double.< n Double.MAX)))
+    "double globals survive a round trip through Lua arithmetic")
+
   (assert-true test
     (Lua.with-lua-do (Lua.libs lua)
                      (Luax.set-bool-global lua "flag" true)
@@ -238,6 +270,23 @@
                          (Luax.get-float-global lua "f")))
     "get-float-global returns Just for existing float")
 
+  (assert-true test
+    (= &(Maybe.Just 3.1415926535897931)
+       &(Lua.with-lua-do (Lua.libs lua)
+                         (Luax.set-double-global lua "d" 3.1415926535897931)
+                         (Luax.get-double-global lua "d")))
+    "get-double-global returns Just for existing number")
+  (assert-true test
+    (Maybe.nothing?
+      &(Lua.with-lua-do (Lua.libs lua) (Luax.get-double-global lua "nope")))
+    "get-double-global returns Nothing for missing global")
+  (assert-true test
+    (Maybe.nothing?
+      &(Lua.with-lua-do (Lua.libs lua)
+                        (Luax.set-string-global lua "s" "hello")
+                        (Luax.get-double-global lua "s")))
+    "get-double-global returns Nothing for wrong type")
+
   (assert-true test
     (= &(Maybe.Just true)
        &(Lua.with-lua-do (Lua.libs lua)
@@ -302,6 +351,24 @@
                          (Luax.get-float-field lua -1 "val")))
     "get-float-field returns Just for existing float field")
 
+  (assert-true test
+    (= &(Maybe.Just 3.1415926535897931)
+       &(Lua.with-lua-do (Lua.libs lua)
+                         (ignore
+                           (Lua.do-string lua
+                                          (cstr "t = {val = 3.141592653589793}")))
+                         (Lua.get-global lua (cstr "t"))
+                         (Luax.get-double-field lua -1 "val")))
+    "get-double-field returns Just for existing number field")
+  (assert-true test
+    (Maybe.nothing?
+      &(Lua.with-lua-do (Lua.libs lua)
+                        (ignore
+                          (Lua.do-string lua (cstr "t = {name = 'Alice'}")))
+                        (Lua.get-global lua (cstr "t"))
+                        (Luax.get-double-field lua -1 "name")))
+    "get-double-field returns Nothing on type mismatch")
+
   (assert-true test
     (= &(Maybe.Just true)
        &(Lua.with-lua-do (Lua.libs lua)
@@ -344,6 +411,17 @@
                      (Lua.get-float lua -1))
     "set-float-field sets a float field on a table")
 
+  (assert-equal test
+    3.1415926535897931
+    (Lua.with-lua-do (Lua.libs lua)
+                     (Lua.create-table lua 0 1)
+                     (Luax.set-double-field lua -1 "val" 3.1415926535897931)
+                     (Lua.set-global lua (cstr "t"))
+                     (Lua.get-global lua (cstr "t"))
+                     (ignore (Lua.get-field lua -1 (cstr "val")))
+                     (Lua.get-double lua -1))
+    "set-double-field sets a double field without losing precision")
+
   (assert-true test
     (Lua.with-lua-do (Lua.libs lua)
                      (Lua.create-table lua 0 1)