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the-art-of-webassembly/ch03/README.md

@@ -17,3 +17,9 @@
 
 - "When you call a JavaScript function
   in WAT, you lose some cycles to overhead. This number isn’t extremely large, but if you execute an external JavaScript function in a loop that iterates 4,000,000 times, it can add up."
+
+### Function Tables
+
+- "Currently, tables only support the anyfunc type (anyfunc is a generic WebAssembly function type), but in the future they might support JavaScript objects and DOM elements as well."
+- "Unlike import objects, JavaScript and WebAssembly can dynamically change tables at runtime."
+- function table 経由での関数呼び出しは indirect なコールになるためパフォーマンスコストがある

the-art-of-webassembly/ch03/table_export.wat

@@ -0,0 +1,25 @@
+(module
+  ;; javascript increment function
+  (import "js" "increment" (func $js_increment (result i32)))
+  ;; javascript decrement function
+  (import "js" "decrement" (func $js_decrement (result i32)))
+
+  (table $tbl (export "tbl") 4 anyfunc) ;; exported table with 4 functions
+
+  (global $i (mut i32) (i32.const 0))
+
+  (func $increment (export "increment") (result i32)
+    (global.set $i (i32.add (global.get $i) (i32.const 1))) ;; $i++
+    global.get $i
+  )
+
+  (func $decrement (export "decrement") (result i32)
+    (global.set $i (i32.sub (global.get $i) (i32.const 1))) ;; $i--
+    global.get $i
+  )
+
+  ;; populate the table
+  ;; the first parameter is the starting index we want to update.
+  (elem (i32.const 0) $js_increment $js_decrement $increment $decrement)
+)
+

the-art-of-webassembly/ch03/table_test.wat

@@ -0,0 +1,14 @@
+(module
+  (import "js" "tbl" (table $tbl 4 anyfunc))
+  ;; import increment function
+  (import "js" "increment" (func $increment (result i32)))
+  ;; import decrement function
+  (import "js" "decrement" (func $decrement (result i32)))
+
+  ;; import wasm_increment function
+  (import "js" "wasm_increment" (func $wasm_increment (result i32)))
+  ;; import wasm_decrement function
+  (import "js" "wasm_decrement" (func $wasm_decrement (result i32)))
+
+  ;; table function type definitions all i32 and take no parameters
+  (type $returns_i32 (func (result i32)))