1 files changed, 148 insertions, 0 deletions
diff --git a/src/core/SkArenaAlloc.cpp b/src/core/SkArenaAlloc.cpp
new file mode 100644
index 0000000000..d6c249b573
--- /dev/null
+++ b/src/core/SkArenaAlloc.cpp
@@ -0,0 +1,148 @@
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include <algorithm>
+#include "SkArenaAlloc.h"
+
+struct Skipper {
+    char* operator()(char* objEnd, ptrdiff_t size) { return objEnd + size; }
+};
+
+struct NextBlock {
+    char* operator()(char* objEnd, ptrdiff_t size) { delete [] objEnd; return objEnd + size; }
+};
+
+SkArenaAlloc::SkArenaAlloc(char* block, size_t size, size_t extraSize)
+    : fDtorCursor{block}
+    , fCursor    {block}
+    , fEnd       {block + size}
+    , fExtraSize {extraSize}
+{
+    if (size < sizeof(Footer)) {
+        fEnd = fCursor = fDtorCursor = nullptr;
+    }
+
+    if (fCursor != nullptr) {
+        this->installFooter(EndChain, 0);
+    }
+}
+
+SkArenaAlloc::~SkArenaAlloc() {
+    this->reset();
+}
+
+void SkArenaAlloc::reset() {
+    Footer f;
+    memmove(&f, fDtorCursor - sizeof(Footer), sizeof(Footer));
+    char* releaser = fDtorCursor;
+    while (releaser != nullptr) {
+        releaser = this->callFooterAction(releaser);
+    }
+}
+
+void SkArenaAlloc::installFooter(FooterAction* releaser, ptrdiff_t padding) {
+    ptrdiff_t releaserDiff = (char *)releaser - (char *)EndChain;
+    ptrdiff_t footerData = SkLeftShift((int64_t)releaserDiff, 5) | padding;
+    if (padding >= 32 || !SkTFitsIn<int32_t>(footerData)) {
+        // Footer data will not fit.
+        SkFAIL("Constraints are busted.");
+    }
+
+    Footer footer = (Footer)(footerData);
+    memmove(fCursor, &footer, sizeof(Footer));
+    Footer check;
+    memmove(&check, fCursor, sizeof(Footer));
+    fCursor += sizeof(Footer);
+    fDtorCursor = fCursor;
+}
+
+void SkArenaAlloc::ensureSpace(size_t size, size_t alignment) {
+    constexpr size_t headerSize = sizeof(Footer) + sizeof(ptrdiff_t);
+    // The chrome c++ library we use does not define std::max_align_t.
+    // This must be conservative to add the right amount of extra memory to handle the alignment
+    // padding.
+    constexpr size_t alignof_max_align_t = 8;
+    auto objSizeAndOverhead = size + headerSize + sizeof(Footer);
+    if (alignment > alignof_max_align_t) {
+        objSizeAndOverhead += alignment - 1;
+    }
+
+    auto allocationSize = std::max(objSizeAndOverhead, fExtraSize);
+
+    // Round up to a nice size. If > 32K align to 4K boundary else up to max_align_t. The > 32K
+    // heuristic is from the JEMalloc behavior.
+    {
+        size_t mask = allocationSize > (1 << 15) ? (1 << 12) - 1 : 32 - 1;
+        allocationSize = (allocationSize + mask) & ~mask;
+    }
+
+    char* newBlock = new char[allocationSize];
+
+    auto previousDtor = fDtorCursor;
+    fCursor = newBlock;
+    fDtorCursor = newBlock;
+    fEnd = fCursor + allocationSize;
+    this->installIntFooter<NextBlock>(previousDtor - fCursor, 0);
+}
+
+char* SkArenaAlloc::allocObject(size_t size, size_t alignment) {
+    size_t mask = alignment - 1;
+    char* objStart = (char*)((uintptr_t)(fCursor + mask) & ~mask);
+    if (objStart + size > fEnd) {
+        this->ensureSpace(size, alignment);
+        objStart = (char*)((uintptr_t)(fCursor + mask) & ~mask);
+    }
+    return objStart;
+}
+
+// * sizeAndFooter - the memory for the footer in addition to the size for the object.
+// * alignment - alignment needed by the object.
+char* SkArenaAlloc::allocObjectWithFooter(size_t sizeIncludingFooter, size_t alignment) {
+    size_t mask = alignment - 1;
+
+    restart:
+    size_t skipOverhead = 0;
+    bool needsSkipFooter = fCursor != fDtorCursor;
+    if (needsSkipFooter) {
+        size_t skipSize = SkTFitsIn<int32_t>(fDtorCursor - fCursor)
+                          ? sizeof(int32_t)
+                          : sizeof(ptrdiff_t);
+        skipOverhead = sizeof(Footer) + skipSize;
+    }
+    char* objStart = (char*)((uintptr_t)(fCursor + skipOverhead + mask) & ~mask);
+    size_t totalSize = sizeIncludingFooter + skipOverhead;
+
+    if (objStart + totalSize > fEnd) {
+        this->ensureSpace(totalSize, alignment);
+        goto restart;
+    }
+
+    SkASSERT(objStart + totalSize <= fEnd);
+
+    // Install a skip footer if needed, thus terminating a run of POD data. The calling code is
+    // responsible for installing the footer after the object.
+    if (needsSkipFooter) {
+        this->installIntFooter<Skipper>(fDtorCursor - fCursor, 0);
+    }
+
+    return objStart;
+}
+
+char* SkArenaAlloc::callFooterAction(char* end) {
+    Footer footer;
+    memcpy(&footer, end - sizeof(Footer), sizeof(Footer));
+
+    FooterAction* releaser = (FooterAction*)((char*)EndChain + (footer >> 5));
+    ptrdiff_t padding = footer & 31;
+
+    char* r = releaser(end) - padding;
+
+    return r;
+}
+
+char* SkArenaAlloc::EndChain(char*) { return nullptr; }
+