From 50a22bcae27a7f947ab77966b55b32477f97f4f5 Mon Sep 17 00:00:00 2001
From: Mark McCaskey <mark@wasmer.io>
Date: Mon, 8 Apr 2019 16:17:34 -0700
Subject: [PATCH] implement emscripten resize_heap

---
 lib/emscripten/src/memory.rs  | 47 +++++++++++++++++++----------------
 lib/runtime-core/src/units.rs |  2 ++
 2 files changed, 28 insertions(+), 21 deletions(-)

diff --git a/lib/emscripten/src/memory.rs b/lib/emscripten/src/memory.rs
index f35dbbb8e2c..9a087401577 100644
--- a/lib/emscripten/src/memory.rs
+++ b/lib/emscripten/src/memory.rs
@@ -1,7 +1,7 @@
 use super::process::abort_with_message;
 use libc::{c_int, c_void, memcpy, size_t};
 use wasmer_runtime_core::{
-    units::{Pages, WASM_MAX_PAGES, WASM_PAGE_SIZE},
+    units::{Pages, WASM_MAX_PAGES, WASM_MIN_PAGES, WASM_PAGE_SIZE},
     vm::Ctx,
 };
 
@@ -25,6 +25,14 @@ pub fn _emscripten_get_heap_size(ctx: &mut Ctx) -> u32 {
     ctx.memory(0).size().bytes().0 as u32
 }
 
+// From emscripten implementation
+fn align_up(mut val: usize, multiple: usize) -> usize {
+    if val % multiple > 0 {
+        val += multiple - val % multiple;
+    }
+    val
+}
+
 /// emscripten: _emscripten_resize_heap
 /// Note: this function only allows growing the size of heap
 pub fn _emscripten_resize_heap(ctx: &mut Ctx, requested_size: u32) -> u32 {
@@ -32,29 +40,26 @@ pub fn _emscripten_resize_heap(ctx: &mut Ctx, requested_size: u32) -> u32 {
     let current_memory_pages = ctx.memory(0).size();
     let current_memory = current_memory_pages.bytes().0 as u32;
 
-    if requested_size > current_memory {
-        let remainder = (requested_size - current_memory) as usize % WASM_PAGE_SIZE;
-        let delta = {
-            let delta = (requested_size - current_memory) as usize / WASM_PAGE_SIZE;
-
-            if remainder != 0 {
-                delta + 1
-            } else {
-                delta
-            }
-        };
-
-        if current_memory_pages.0 as usize + delta > WASM_MAX_PAGES {
-            // TODO: handle this?
-            debug!("Can't exceed max pages");
-            return 0;
+    // implementation from emscripten
+    let mut new_size = usize::max(current_memory as usize, WASM_MIN_PAGES * WASM_PAGE_SIZE);
+    while new_size < requested_size as usize {
+        if new_size <= 0x2000_0000 {
+            new_size = align_up(new_size * 2, WASM_PAGE_SIZE);
+        } else {
+            new_size = usize::min(
+                align_up((3 * new_size + 0x8000_0000) / 4, WASM_PAGE_SIZE),
+                WASM_PAGE_SIZE * WASM_MAX_PAGES,
+            );
         }
+    }
 
-        if let Ok(v) = ctx.memory(0).grow(Pages(delta as u32)) {
-            return v.0;
-        }
+    let amount_to_grow = (new_size - current_memory as usize) / WASM_PAGE_SIZE;
+    if let Ok(_pages_allocated) = ctx.memory(0).grow(Pages(amount_to_grow as u32)) {
+        debug!("{} pages allocated", _pages_allocated.0);
+        1
+    } else {
+        0
     }
-    0
 }
 
 /// emscripten: getTotalMemory
diff --git a/lib/runtime-core/src/units.rs b/lib/runtime-core/src/units.rs
index 982baefcbe6..e8232efc8aa 100644
--- a/lib/runtime-core/src/units.rs
+++ b/lib/runtime-core/src/units.rs
@@ -6,6 +6,8 @@ use std::{
 
 pub const WASM_PAGE_SIZE: usize = 65_536;
 pub const WASM_MAX_PAGES: usize = 65_536;
+// From emscripten resize_heap implementation
+pub const WASM_MIN_PAGES: usize = 256;
 
 /// Units of WebAssembly pages (as specified to be 65,536 bytes).
 #[derive(Serialize, Deserialize, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]