asm.js

@@ -87,6 +87,8 @@ const State = Object.freeze({
     GLOBAL_NAME:  15,
     GLOBAL_TYPE:  16,
     GLOBAL_INIT:  17,
+    AT_MEM:       18,
+    AT_ADDR:      19,
 });
 
 const Action = Object.freeze({
@@ -100,6 +102,7 @@ const Action = Object.freeze({
     MEM:    7,
     IMPORT: 8,
     GLOBAL: 9,
+    AT:     10,
 });
 
 const types = {
@@ -142,6 +145,7 @@ class Parser {
             ".mem":    State.MEM_NAME,
             ".import": State.IMPORT_NAME,
             ".global": State.GLOBAL_NAME,
+            ".at":     State.AT_MEM,
         };
         this.handlers = {
             [State.TOP]:          (token) => this.token_top(token),
@@ -162,6 +166,8 @@ class Parser {
             [State.GLOBAL_NAME]:  (token) => this.token_global_name(token),
             [State.GLOBAL_TYPE]:  (token) => this.token_global_type(token),
             [State.GLOBAL_INIT]:  (token) => this.token_global_init(token),
+            [State.AT_MEM]:       (token) => this.token_at_mem(token),
+            [State.AT_ADDR]:      (token) => this.token_at_addr(token),
         };
 
         this.results = [];
@@ -425,6 +431,27 @@ class Parser {
         }
     }
 
+    token_at_mem(token) {
+        this.at = { mem: token };
+        this.state = State.AT_ADDR;
+    }
+
+    token_at_addr(token) {
+        const value = this.integer(token);
+        if (value == null) {
+            console.error(
+                `ERROR: Unexpected token {token} in .mem: expected address`);
+            this.at = undefined;
+            return;
+        }
+
+        this.at.addr = value;
+        const action = { type: Action.AT, at: this.at };
+        this.at = undefined;
+        this.state = State.TOP;
+        return action;
+    }
+
     mem_action() {
         const action = {
             type: Action.MEM,
@@ -476,6 +503,7 @@ export class Assembler {
             [Action.MEM]:    (action) => this.action_mem(action),
             [Action.IMPORT]: (action) => this.action_import(action),
             [Action.GLOBAL]: (action) => this.action_global(action),
+            [Action.AT]:     (action) => this.action_at(action),
         };
 
         this.exports = [];
@@ -483,6 +511,7 @@ export class Assembler {
         this.mems = {};
         this.imports = [];
         this.globals = {};
+        this.pos = { mem: 0, addr: 0 };
 	}
 
     action_append(action) {
@@ -549,6 +578,16 @@ export class Assembler {
         Object.assign(this.globals, action.global);
     }
 
+    action_at(action) {
+        const mem = Object.keys(this.mems).indexOf(action.at.mem);
+        if (mem == -1) {
+            console.error(`ERROR: No memory named {action.at.mem}`);
+            return;
+        }
+        this.pos.mem = mem;
+        this.pos.addr = action.at.addr;
+    }
+
 	push(chunk) {
 		const text = this.decoder.decode(chunk, { stream: true });
 		for (const action of this.parser.handle(text))