Make all sections optional

asm.js

@@ -78,7 +78,7 @@ const State = Object.freeze({
     LOCAL_NAME:   6,
     LOCAL_TYPE:   7,
     MEM_NAME:     8,
-    MEM_INITIAL:  9,
+    MEM_INIT:     9,
     MEM_MAX:      10,
     MEM_FLAGS:    11,
     IMPORT_NAME:  12,
@@ -95,6 +95,8 @@ const State = Object.freeze({
     ALIGN:        23,
     DEF_NAME:     24,
     DEF_VALUE:    25,
+    BLOCK_NAME:   26,
+    BLOCK_TYPE:   27,
 });
 
 const Action = Object.freeze({
@@ -113,21 +115,32 @@ const Action = Object.freeze({
     ALIGN:  12,
     DEF:    13,
     LABEL:  14,
+    ENTER:  16,
+    EXIT:   17,
+    ELSE:   18,
 });
 
 const types = {
+    "void": 0x40,
     "func": 0x60,
     "i32":  0x7f,
 };
 
 const opcodes = {
+    "block":      0x02,
+    "loop":       0x03,
+    "if":         0x04,
+    "else":       0x05,
     "end":        0x0b,
+    "br":         0x0c,
+    "br_if":      0x0d,
     "local.get":  0x20,
     "local.set":  0x21,
     "local.tee":  0x22,
     "global.get": 0x23,
     "global.set": 0x24,
     "i32.const":  0x41,
+    "i32.gt_u":   0x4b,
     "i32.mul":    0x6c,
 };
 
@@ -163,6 +176,7 @@ class Parser {
             ".align":  State.ALIGN,
             ".def":    State.DEF_NAME,
         };
+        this.blocks = new Set(["block", "loop", "if"]);
         this.handlers = {
             [State.TOP]:          (token) => this.token_top(token),
             [State.EXPORT]:       (token) => this.token_export(token),
@@ -190,6 +204,8 @@ class Parser {
             [State.ALIGN]:        (token) => this.token_align(token),
             [State.DEF_NAME]:     (token) => this.token_def_name(token),
             [State.DEF_VALUE]:    (token) => this.token_def_value(token),
+            [State.BLOCK_NAME]:   (token) => this.token_block_name(token),
+            [State.BLOCK_TYPE]:   (token) => this.token_block_type(token),
         };
 
         this.results = [];
@@ -220,17 +236,33 @@ class Parser {
     token_top(token) {
         if (token == LINE_END)
             return;
-        let state;
-        if (state = this.directives[token]) {
+        const state = this.directives[token];
+        if (state) {
             this.state = state;
             return;
         }
+
         if (token.endsWith(":"))
             return { type: Action.LABEL, name: token.slice(0, -1) };
-        const code = this.translate_code(token);
-        if (code)
-            return { type: Action.APPEND, code };
-        else
+
+        const opcode = opcodes[token];
+
+        if (this.blocks.has(token)) {
+            this.state = State.BLOCK_NAME;
+            this.block = { code: opcode };
+            return;
+        }
+        if (token == "else")
+            return { type: Action.ELSE }
+        if (token == "end")
+            return { type: Action.EXIT };
+
+        if (opcode)
+            return { type: Action.APPEND, opcode };
+        const literal = this.integer(token);
+        if (literal)
+            return { type: Action.APPEND, literal };
+
         return { type: Action.SYMBOL, symbol: token };
     }
 
@@ -574,6 +606,36 @@ class Parser {
         return action;
     }
 
+    token_block_name(token) {
+        if (token == LINE_END) {
+            this.block.type = types["void"];
+            const action = { type: Action.ENTER, block: this.block };
+            this.state = State.TOP;
+            this.block = undefined;
+            return action;
+        } else {
+            this.block.label = token;
+            this.state = State.BLOCK_TYPE;
+            return;
+        }
+    }
+
+    token_block_type(token) {
+        if (token == LINE_END) {
+            this.block.type = types["void"];
+        } else {
+            this.block.type = types[token];
+            if (this.block.type == undefined) {
+                console.error(
+                    `ERROR: Unexpected token ${token}, expected type`);
+            }
+        }
+        const action = { type: Action.ENTER, block: this.block };
+        this.state = State.TOP;
+        this.block = undefined;
+        return action;
+    }
+
     mem_action() {
         const action = {
             type: Action.MEM,
@@ -588,10 +650,11 @@ class Parser {
 	*handle(src) {
         let action;
 		for (const token of this.tokenizer.handle(src)) {
-            if (action = this.handlers[this.state](token))
+            if (action = this.handlers[this.state](token)) {
                 yield action;
             }
         }
+	}
 }
 
 const Section = Object.freeze({
@@ -631,6 +694,9 @@ export class Assembler {
             [Action.ALIGN]:  (action) => this.action_align(action),
             [Action.DEF]:    (action) => this.action_def(action),
             [Action.LABEL]:  (action) => this.action_label(action),
+            [Action.ENTER]:  (action) => this.action_enter(action),
+            [Action.EXIT]:   (action) => this.action_exit(action),
+            [Action.ELSE]:   (action) => this.action_else(action),
         };
 
         this.exports = [];
@@ -641,10 +707,14 @@ export class Assembler {
         this.pos = { mem: 0, addr: 0 };
         this.data = [];
         this.defs = {};
+        this.blocks = [];
 	}
 
     action_append(action) {
-        this.funcs[this.current_func].body.push(action.code);
+        const code = action.opcode != undefined
+              ? [ action.opcode ]
+              : this.leb128(action.literal);
+        this.funcs[this.current_func].body.push(...code);
     }
 
     action_export(action) {
@@ -676,17 +746,22 @@ export class Assembler {
 
     action_symbol(action) {
         const func = this.funcs[this.current_func];
-        const value = this.lookup_param(func, action.symbol)
+        const value = this.lookup_block(action.symbol)
+              ?? this.lookup_param(func, action.symbol)
               ?? this.lookup_local(func, action.symbol)
               ?? this.lookup_global(action.symbol)
-              ?? this.lookup_def(action.symbol);
         if (value == null) {
+            const def_value = this.lookup_def(action.symbol);
+            if (def_value == null) {
                 console.error(
                     `ERROR: Unable to resolve symbol ${action.symbol}`);
-            value = 0;
+                return;
             }
+            func.body.push(...this.leb128(def_value));
+        } else {
             func.body.push(value);
         }
+    }
 
     action_mem(action) {
         Object.assign(this.mems, action.mem);
@@ -748,12 +823,34 @@ export class Assembler {
         this.defs[action.name] = this.pos.addr;
     }
 
+    action_enter(action) {
+        this.funcs[this.current_func].body.push(action.block.code);
+        this.funcs[this.current_func].body.push(action.block.type);
+        this.blocks.push(action.block.label);
+    }
+
+    action_exit(action) {
+        this.funcs[this.current_func].body.push(opcodes.end);
+        this.blocks.pop();
+    }
+
+    action_else(action) {
+        this.blocks.pop();
+        this.funcs[this.current_func].body.push(opcodes.else);
+        this.blocks.push(undefined);
+    }
+
 	push(chunk) {
 		const text = this.decoder.decode(chunk, { stream: true });
 		for (const action of this.parser.handle(text))
             this.handlers[action.type](action);
 	}
 
+    lookup_block(symbol) {
+        const index = this.blocks.toReversed().indexOf(symbol);
+        return index == -1 ? null : index;
+    }
+
     lookup_param(func, symbol) {
         const index = Object.keys(func.params).indexOf(symbol);
         return index == -1 ? null : index;
@@ -787,6 +884,7 @@ export class Assembler {
 
     wasm_section_type() {
         const funcs = Object.values(this.funcs);
+        if (funcs.length == 0) return null;
         const contents = funcs.map(({ params, results }) => {
             const param_types = Object.values(params);
             return [
@@ -820,6 +918,7 @@ export class Assembler {
 
     wasm_section_func() {
         const func_count = Object.entries(this.funcs).length;
+        if (func_count == 0) return null;
         return [ func_count, ...Array(func_count).keys() ];
     }
 
@@ -843,6 +942,7 @@ export class Assembler {
 
     wasm_section_export() {
         const exports = Object.entries(this.exports);
+        if (exports.length == 0) return null;
         const contents = exports.map(([ name, { kind, index }]) => {
             const name_utf8 = this.encoder.encode(name);
             return [
@@ -857,6 +957,7 @@ export class Assembler {
 
     wasm_section_code() {
         const funcs = Object.values(this.funcs);
+        if (funcs.length == 0) return null;
         const contents = funcs.map(({ body, locals }) => {
             const local_types = Object.values(locals);
             const local_count = local_types.length;
@@ -887,7 +988,7 @@ export class Assembler {
             return [
                 ...(loc.mem == 0 ? [ 0 ] : [ 2, loc.mem ]),
                 opcodes["i32.const"],
-                loc.addr,
+                ...this.leb128(loc.addr),
                 opcodes["end"],
                 data.length,
                 ...data,
@@ -921,4 +1022,18 @@ export class Assembler {
         else
             return [ flags, init ];
     }
+
+    leb128(x) {
+        const orig = x;
+        const bytes = [];
+        while (true) {
+            const b = x & 0x7f;
+            x >>= 7;
+            if (x == 0 && (b & 0x40) == 0 || x == -1 && (b & 0x40) != 0) {
+                bytes.push(b);
+                return bytes;
+            }
+            bytes.push(b | 0x80);
+        }
+    }
 }